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Paolo TARTARINI

Professore Ordinario presso: Dipartimento di Ingegneria "Enzo Ferrari"


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Pubblicazioni

2020 - A simple test method for measurement of the interface thermal resistance of coated and uncoated metal surfaces [Relazione in Atti di Convegno]
PEDRAZZI, Simone; Vergnano, A.; Allesina, G.; VERONESI, Paolo; Leali, F.; Tartarini, P.; Muscio, A.
abstract

Dies for metal casting must often be coated internally to minimize interaction between the surface of the steel die and the melt metal during pouring and solidification. However, the added coating increases the thermal interface resistance during the cooling process and can thus extend the process duration. For example, numerical predictions and experimental results are matched if the interface resistance is even quintupled in the presence of usual interface coating, compared to the uncoated mold. In order to have a reasonable estimate of the interface thermal resistance, an easy to use measurement approach has been tested. This consists of contacting a cold and a hot samples of metals with known thermal properties, one at ambient temperature and the other one much hotter. The temperatures of the two samples, assumed to be uniform in each sample, are measured by thermocouples, and the interface resistance is retrieved from the time evolution pattern of those temperatures during the thermal transient that follows the instant in which the samples have been contacted.


2020 - Analisi di stabilità dei modi entro piano di motociclette da competizione mediante modellazione multicorpo simbolica [Tesi di dottorato]
Cattabriga, Stefano
abstract

Experimental evidence shows that road racing motorcycles are often subject to peculiar stability issues, which commonly arise due to the high stresses that all mechanical parts and systems suffer in this kind of vehicles. These events generally consist of self-excited vibrations, which involve one or more elements of the motorcycle. Several studies can be found in the literature on this subject, dealing with different instability phenomena, e.g. chatter, weave, wobble, front wheel patter. Each of them can be identified with a mode of vibration of the motorcycle, with its own typical frequency and modal shape, which can be reproduced by suitable multibody models. The aim of this work is to identify the switching mechanisms of these self-excited vibrations, focusing on the in-plane modes of the motorcycle. To this purpose, novel tools for stability analysis are employed, along with root loci and time domain simulations, which have a wider documented use in the literature. In particular, a numerical algorithm is developed for computing stability maps descending from symbolic algebra multibody models. In this thesis the two main instability mechanisms that affect the motorcycle longitudinal dynamics are studied, the so-called “chatter” of rear wheel and “patter” of front wheel, both of them consisting of self-excited vibrations which can arise during heavy braking in straight motion. In both kinds of motion, the out-of-plane components are negligible, or they are not a necessary condition to the onset of instability, hence planar multibody models are employed, with rigid bodies. The full motorcycle multibody models employed feature all the relevant moving parts of the vehicle, therefore they are suitable to carry on transient manoeuvres in the time domain. The stability of these models is studied next to modal analysis of reduced or simplified models with the lowest possible number of degrees of freedom. These minimal models represent sub-systems of the vehicle, since they are designed in order to capture the essential characteristics of the specific instability mechanism under study, taking into account only the elements which are necessary to the onset of the self-excited vibrations. Taking advantage of the simplicity of these models, the equations of motion are linearised in steady-state conditions, and the system matrices are analysed to highlight the crucial parameters that can bring the actual vehicle to instability. Experience of race engineers and riders confirms that in motorcycles all kinds of instability are always to prevent, since they weaken the vehicle overall performance, due to the severe oscillations of the tyre-ground vertical loads that can arise, causing a loss of grip and making the vehicle harder to control. The results of the present work give a comprehensive description of the in-plane instability phenomena of a racing motorcycle, highlighting the parameters that play a key role in the onset of chatter and patter vibrations. In particular, the geometry of the rear (swing-arm) and front (telescopic fork) suspensions are demonstrated to have major role in the unstable phenomena, together with their damping and stiffness. The roles of the chain transmission and of the structural compliance of the frame and the forks are also studied. These results can be useful to prevent instability, by careful design of the motorcycle elements, by the correct choice of stiffness and damping parameters or by introduction of new devices on the vehicle.


2020 - Analisi elastoidrodinamica di contatti lubrificati in motori a combustione interna: gestione dei problemi di cavitazione e contatto diretto [Tesi di dottorato]
FERRETTI, ANDREA
abstract

The continuous demand of even-higher efficiency in internal combustion engines has led to a growing interest in the study of their internal losses’ mechanisms. In particular, a large amount of friction losses is registered at engine’s bearings, whose correct definition deeply affects the achievement of the desired performances. The design of the layout of engine’s lubricated contacts is one of the first design choices to be addressed and a modification of their quotas usually involves an almost complete engine’s redesign. The developing of simulation methodologies able to evaluate the adequacy of the design choices concerning the lubricated contacts is therefore fundamental, in order to considerably reduce the number of trial-and-errors steps usually required in the design process of an engine. This activity deals with the problem of simulating lubricated contacts, mainly focusing on the developing of a proper approach to the analysis of the asperity contact problem. The hydrodynamic problem will be tackled adopting a mass-conserving algorithm, which uses a linear complementary formulation of the Reynolds equation to calculate the hydrodynamic pressure distribution within the lubricant film and to identify the cavitated region at given oil film height. Great attention will be paid to the methodology used to deal with cases of mixed lubrication, in which a partial direct metal-to-metal contact occurs. Two different methodologies will be investigated, the first based on a complementary formulation of the asperity contact problem and the latter based on the theory introduced by Greenwood and Williamson and then deepened by Greenwood and Tripp. This theory introduces a direct relationship between the asperity contact pressure and the gap between the two mating surfaces, obtained by statistically evaluating the probability that two asperity peaks come into contact and approximating each peaks’ contact according to the Hertzian theory. The derived methodology is then applied to the elastohydrodynamic analysis of the conrod small-end/piston-pin coupling of a high performance Ducati motorcycle engine. In order to calibrate the asperity contact model based on the Greenwood and Tripp theory, some non-standard roughness parameters are necessary, useful to describe the entire profile from a statistical point of view. The meaning and value assumed by these parameters will be investigated by directly measuring the roughness profiles of the two mating surfaces and implementing a procedure able to calculate them, starting from their definition. It will be shown how, by adopting different calibrations of the asperity contact model, it is possible to identify similar critical areas, in good agreement with empirical evidences of small end failures occurred during preliminary tests conducted at an early stage of the engine design process and under severe loading conditions. However, the absolute values of the various quantities involved are significantly different, making it difficult to identify admissible threshold values capable of defining the critical state of the components.


2020 - Caratterizzazione a fatica delle leghe AlSi7Mg, Ti6Al4V e X3NiCoMoTi prodotte mediante Laser Powder Bed Fusion [Tesi di dottorato]
DEFANTI, SILVIO
abstract

In the last years, Laser Powder Bed Fusion (L-PBF) has become the main technology to produce metal parts by Additive Manufacturing (AM). This manufacturing technique comprises the advantages of additive manufacturing and the high performance offered by metal alloys in order to produce mechanical components ready for the final application. Occasionally, due to the layer-wise process, some defects can be produced inside the parts, leading to mechanical properties that are well above the requirements for static loads but rapidly decay under fatigue conditions. This concern leads the researchers to investigate the actual mechanical properties of parts, as compared to those of traditionally manufactured components, and to optimize the whole process in order to limit defects and increase the reliability of the process. While extensive static tests confirmed high mechanical properties of the main metal alloys produced by AM, the fatigue behavior of additive metal parts still needs to be deeply investigated. In this study, the fatigue and tensile properties of 3 metal alloys were analyzed, in view of 3 final applications, listed as follows. • Automotive field: Aluminum alloy AlSi7Mg was studied for the final production of a topologically optimized frame part of a sports car. In particular, the interest was focused on the effect of: - Heat treatment: no heat treatment vs. T6 vs. the heating cycle required for painting the body-in-white frame; - Surface finish: as-built vs. polished; - Orientation on the building platform. • Medical field: Titanium alloy Ti6Al4V was investigated for the production of femoral stems with improved osseointegration. The study on this material was focused on the effect of: - Powder contamination; - Different parameters/powder sets; - Surface finish: as-built vs. polished; - Orientation on the building platform. • Mold manufacturing field: the Maraging steel alloy X3NiCoMoTi was studied for the application in a mold insert with internal cooling channels. The main concern related to this application led to the study of the effect of: - Holes in the material, acting as stress concentrators; - Surface finish of the holes; - Different parameters/powder sets. This work aims to provide better understanding of the critical variables of the manufacturing process and the post-processing operations. This study was accomplished within the European Project DREAM (Driving Up Reliability of Additive Manufacturing)


2020 - Caratterizzazione e applicazioni di miscele di PLA con polifenoli da datteri [Tesi di dottorato]
Shaikh Zadeh, Khadija
abstract

Polylactic acid (PLA) is a thermoplastic biodegradable polymer derived from renewable resources. It is one of the most consumed biodegradable polymers in the world due to a wide range of commodity applications. PLA has some weaknesses such as low thermal stability, impact strength and ductility; therefore many research studies are focused on PLA modification to extend its range of applications. One approach is to add modifiers in order to enhance its properties. Date palm fruit (DPF) is a rich source of polyphenols, that are considered as effective antioxidants because of their high capacity in scavenging free radicals, that have health promoting effects in the prevention of degenerative diseases. Polyphenols also act as plasticizers and possible thermal stabilizers in polymers. In this research, a set of PLA/DPF extracted polyphenols were prepared and analyzed for medical applications, as well as for thermal stability improvement. The first blends were prepared by electrospinning to be used as cell culture scaffolds for tissue engineering applications. The results revealed that the scaffolds became more hydrophilic after the addition of polyphenols. It was also found that both cell proliferation and cell viability were enhanced with increased polyphenol concentration in the scaffolds. A second set of PLA samples containing different concentrations of the polyphenol extract were prepared by extrusion. The morphology, mechanical and thermal properties were determined, and it was found that the presence of polyphenol in PLA (i) improved its thermal stability, (ii) decreased Young’s modulus and tensile strength, and (iii) increased the elongation at break of the blend samples. The glass transition temperature were determined through dynamic mechanical analysis (DMA). The results showed a broadening in the tan  peak, and a gradual decrease in the peak temperature with increasing polyphenol content in PLA, which confirmed that the polyphenol increased the free volume in PLA and thus acted as a plasticizer.


2020 - L’efficientamento energetico degli edifici storici attraverso analisi condotta con metodologia dinamica. Il caso studio del Palazzo Ducale di Modena. [Tesi di dottorato]
MALAGUTI, VANIA
abstract

This PhD thesis focuses on energy consumption and behavior of envelope and HVAC system in historical-constrained buildings. The main target is to study a methodology for the energy retrofitting solutions in these particular buildings. In Europe this issue is very relevant, because historical buildings are widespread in the area (it is estimated that in Europe about a quarter of existing buildings were built before the middle of the last century). The interest in these buildings derives from the inapplicability of traditional energy requalification methods and from the need for a different theoretical and practical approach. The uses of these buildings are manifold but they have constructive characteristics that unite them and distinguish them from all other buildings, as instance the very massive perimeter structures and the high thermal inertia, the large heated volumes, rooms and zones often used in a discontinuous way, the inefficiency of heating systems and the very high consumption and energy waste. This thesis project focuses on the development of innovative and cost-effective advantageous energy design solutions for historical buildings, which are able to offer significant improvements in energy performance while ensuring internal comfort requirements and non-invasive and reversible characteristics. The project, with the use of a case study, will demonstrate the effectiveness of the technologies, methodologies, systems or tools developed and the potential for replicability of the proposed solutions. The case study is the Ducal Palace of Modena, a magnificent historic-constrained building representing Modena city all over the world. In past centuries, the Palace was the seat of the “Estensi Duke”; today it is home of the prestigious Military Academy, a training school for officers of the Italian National Army. The general objective of the project is achieved through the following main activities: - Analysis of the state of the art of energy efficiency procedures for historic buildings and the relevant EU legislative framework; - Definition of a complete methodology for the energy retrofitting solutions of historic-constrained buildings, with the use of the case study of the Ducal Palace of Modena. The methodology will be based on an in-depth cognitive analysis of the building, in particular the envelope and HVAC system. - Through the study of the properties of materials, the use of thermal systems and the analysis of energy consumption over the years, an energy audit of the building will be performed. The study of the actual state and the simulations of the various proposed energy retrofit interventions will be performed with a dynamic simulation software in order to take the high thermal inertia of the building into account. - Through a parametric analysis and a normalization of the results, a series of complete decision-making guidelines are developed for the energy retrofitting of historic buildings in order to export a common methodology applicable to this particular type of building all around Europe.


2020 - Modellazione ed analisi di sistemi meccanici operanti nell’industria del packaging [Tesi di dottorato]
Di Canosa, Raffaele
abstract

The development of robust and reliable systems in the packaging industry requires the creation and the validation of physical models that can estimate both the mission profile of the components and the sub-assemblies and can provide data related to the status of the system when operating out of the nominal working condition. The object of the study is a complex mechanical system operating with liquid products filled in a package obtained by overlaying polymeric, metallic and organic materials. The mechanism ensures the execution of several phases, hence it is subjected to multiple stresses, which are both cyclically applied during the standard functioning of the automated machine and which occur randomly in case of deviation from the nominal working conditions. The study was carried out focusing on three main aspects: the modelling of the entire system and the specific analysis of one of the sub-assemblies, the creation of a test bench for collecting data and validating the model, the correlation of the data with the information provided by the equipment installed on the field. The mechanical model of the system has been developed using the commercial multi-body software MSC Adams®. Due to the complexity of the mechanism, the analysis of the kinematic and the dynamic response of the system was executed by incremental steps, reducing the assembly in simpler sub-systems and evaluating their behaviour in operating conditions which were representative of the real application, even if they were less complex. The achievements and the characteristic parameters identified in the simplified models were extended to the entire system, in order to improve the model and tune the calculated response based on the measurements collected. One part of the analysis has focused on one specific subsystem, which had the function of cutting the material used for the packaging of the products. The study investigated the parameters competing to the cutting efficiency. The coherence between the mechanical model and the physical system was investigated and validated by the measurements collected on a test rig. The testing equipment was a simplified version of the real mechanism, that was able to emulate the majority of the stresses applied in the operative life of the machine. Customized sensors were designed and manufactured in order to measure some of the forces exchanged among the sub-assemblies of the system. The kinematic response of the model was used for defining in terms of time and space the sequence of the events which characterize the system and for identifying the impulsive forces that the sub-systems exchange with the frame, that was equipped with some accelerometers. The correlation between the sequence of events calculated with the virtual model and the data collected with the accelerometers, required the simplification of the system, first by decomposing and inhibiting some of the stresses both in the model and in the test rig and then applying them in sequence up to the full integration inf the complete system. The results were then compared with the data provided by a healthy and damaged system.


2020 - Modelli di resistenza per predire il comportamento sia degli overlays in HPFRCC/UHPFRC sia dell'interfaccia di collegamento di strutture composite riabilitate in NSC - HPFRCC/UHPFRC [Tesi di dottorato]
SAVINO, VINCENZO
abstract

The first part of this phD thesis will present a generalized model that predicts the compressive, tensile and bending flexural responses of any HPFRCC/UHPFRC, as the matrix strength, the aspect ratio and the amount of fibers change. The model has been calibrated on the basis of a comprehensive experimental investigation carried out on both lab specimens and full-scale structural beams made of different fiber-reinforced-concretes. The proposed model not only extends the range of application of the existing ones to the family of UHPFRC materials, but also introduces the prediction of the post-cracking tensile response. An analytical calculation based on the ``Composite Material Theory" (CMT) can estimate the bending flexural response once the compressive and the tensile behaviors are predicted by the model. The model may therefore be useful to correlate the different mechanical tests of characterization requested for a given product; for example, if the compressive and tensile responses of a given HPFRCC or UHPFRC are measured or predicted by the model, the latter can estimate the results of bending flexural tests. Moreover, the model permits to minimize the manufacturing costs of the commercial product, by detecting the optimal type and the minimal dosage of fibers necessary to meet the mechanical performances required. The model has been adopted in a practical case in order to virtually optimize the type and the dosage of fibers embedded in an existing UHPFRC structure. The second part of this PhD thesis will present a theoretical cohesive-based model that predicts the load carrying capacity of an existing concrete structure overlaid with a layer of HPFRCC/UHPFRC, by varying both the type of overlay and the moisture level of the substrate surface prior to overlay. Several bond tests were designed by the author in order to accurately characterize the peeling-crack (mode I), the shear-slip (mode II) relationships and the coupling factor between mode I and II. The experimental data were used for calibrating the model. A further experimental campaign was carried out for confirming the reliability of the model. A FEM was developed in order to numerically reproduce the propagation of the damage process at the interface. The numerical simulations were compared with the experimental results. The FE interface was modeled with a proper nonlinear cohesive law which couples the relationships of mode I with mode II on the basis of the experimental data.


2020 - Procedure per la valutazione della tensione normale interlaminare in laminati curvi in composito modellati agli elementi finiti: valutazioni critiche e applicazioni su componenti di Formula Uno. [Tesi di dottorato]
Fanelli, Sergio
abstract

Composite materials as carbon fiber reinforced polymer are often used in many industrial fields, specially where lightweight design is the prerogative to extract performance from structural components, some examples are automotive, aerospace, or sports equipment structures. Anisotropy is the main feature of composites materials, on one side this property is cleverly used to obtain a remarkable performance/weight ratio on, but on the other side there's a complex stress state to evaluate. The present contribution deals with the evaluation of the normal component of interlaminar stress in curved composite laminates subject to remote loads. Although those stress components are usually smaller than their in-plane counterparts, the comparably limited adhesion strength of the interlaminar interfaces causes the experience of delaminations, specially in curved laminates, resulting in reduced stiffness and strength of the structural component, and even a higher probability of failure or need for premature component substitution. A Finite Element (FE) model is nowadays usually required during the design phase in order to evaluate composite components behavior by a stress and stiffness point of view. Shell finite elements models are often used for composite components due to their computational efficiency and modeling flexibility mixed with discrete accuracy in terms of displacements results and in-plane stresses estimation. Nevertheless, the customary shell finite element formulation neglects the contribution of the Interlarminar Normal Stress (ILNS) component to internal energy and to the stress state characterization. A good estimation of what is the interlaminar stress state of a composite component could be obtained with solid FE models, or mixed 2D/3D FE models, or cohesive elements and surfaces. But a model developed for post-processing and implemented with linear shell element types may represent a good opportunity to maintain the FE model complexity at reasonable levels. The model for the evaluation of ILTS under investigation requires information about curvatures that can be obtained by a simple shell FE model, and it is applied on a four point bending test case which is usually adopted for ILNS evaluation of composite components. The experimental results and the model results are compared and a solid FE model is added to the comparison. Furthermore, the applicability of the model on a more complex matrix is investigated, using as a case study a Formula One front wing. A test case consisting in a static loading is evaluated and also a dynamic load case involving a modal transient analysis.


2020 - Progettazioni di plastiche derivanti dal vino: scarti vitivinicoli come substrato di sintesi, additivi e fillers per differenti polimeri e biopolimeri. [Tesi di dottorato]
NANNI, ALESSANDRO
abstract

In the last decades, the increasing global environmental concern has lead industry and scientific academia to focus in new eco-friendly and renewable processes, materials and systems. Considering the plastics sector, biodegradable and bio-based polymers have gained a great attention as promising solutions to solve or reduce the crude oil dependence and/or the plastic pollution issues. By the way, these natural polymers still cover restricted portion of the market because of both their higher prices and the lack of knowledge, if compared with classical petrochemical polymers. Therefore, from an overall point of view, the present dissertation should be seen as a detailed part of a broader context in which it is attempted to bridge the maturity gap between the concepts of petrochemical and bio-refineries and to promote their progressive switch in large-scale by the contribution of new ideas, results and know-hows. Going into details, the present work has investigated the possibility to valorize the agro-industrial wastes derived from the wine companies within different polymers and biopolymers through several approaches. Two apparently distinct processes as plastic and winemaking have been put in contact, offering new suitable products able to solve at the same time the green materials necessity and the agro-wastes disposal problems in accordance with the principles of sustainability, circular economy, renewability and low environmental footprint. Different solid wine wastes have been collected, characterized and exploited in different ways depending on their evaluated properties and potentiality. Generally, wastes rich in polyphenols and/or their extracts have been tested as natural stabilizers within Polypropylene (PP), Poly(hydroxybutyrate) (PHB) and Poly(butylene Succinate) (PBS) investigating the response of the bio-stabilizers to short and long-terms degradation (thermal and/or UV) as well as to biodegradation in different environments. At the same time, wastes with high inorganic or lignocellulosic fractions have been studied as reinforcement cost-effective natural fillers within Poly(hydroxybutyrate) (PHB), Poly(3-hydroxybutyrate-co-hydroxyhexanoate) (PHBH), Poly(3-hydroxybutyrate-co-hydroxyvalerate) (PHBV), Poly(butylene Succinate) (PBS), Polyamide 11 (PA11) and Poly(lactic acid) (PLA). Bio-composites have been mainly investigated from a thermal, mechanical and rheological point of view, exploiting also micro-mechanics models to deeper understand the effect of the wine-derived fillers on the biopolymers properties. Finally, steps to directly synthesise scl-Poly(hydroxyalkanoate)s (PHAs) starting from wine wastes as substrate have been also partially discussed. Each treated topic has been handled from a theoretical and experimental point of view in order to model and control the behaviour of these new wine-based materials and simultaneously, economical essays have been carried out in order to point out the concrete feasibility to transfer these wine-based materials to large-scale apparatuses.


2020 - Progressi nel condizionamento del gas di sintesi per impianti di gassificazione di piccola taglia [Tesi di dottorato]
MORSELLI, NICOLO'
abstract

The transition towards sustainable energy development involves the efficiency improvement of the processes, the current technologies, and the ever increasing use of renewable energy sources. In this scenario, biomasses have the potential to constitute a low environmental impact energy reservoir that can be used in the combined production of electrical and thermal energy. Among the different methods of energy conversion of lignocellulosic biomass, gasification applied to CHP gensets emerges due to the high electrical efficiency and scalability, which make it applicable also outside purely industrial contexts. The key to large-scale using of small-scale gasification plants lies in the ability to produce simple and effective filtration systems with a low maintenance cost. In order to pursue these objectives it is essential to have a deep knowledge of the phenomena of multiphase fluid dynamics, as well as of the thermal exchanges that take place in gasification plants. To this end, this thesis work is divided into two sections: the first in which the theoretical frame of reference is constructed, aimed at defining the thermo-fluid dynamic variables at stake, and a second operative part in which a series of solutions are proposed, ranging from hot filtration, up to the use of biological means to reduce pollutants. Specifically, the first chapter will introduce the different processes and technologies available for the energy conversion of biomasses, including them in the broader European renewable energy scenario. The gasification process of woody biomasses for the production of electricity will be described, reviewing the main components common to this type of plant. The key theme of this thesis will therefore be anticipated by describing the currently available techniques for the filtration of the syngas, focusing on the methods of conditioning its physical properties. The second chapter will deal with the effects of pollutants, present in the syngas, on the mechanical parts of internal combustion engines thus fueled. The psychrometric approach, supported by computational methods, will allow to know the optimal conditions for a safe operation of these generators. The third chapter will describe the experimental characterization of a filter made with biochar from gasification, carried out on a micro biomass CHP plant. This study will lay the foundations for what will be discussed in the next chapter, namely the design and study, both experimental and numerical, of a heat exchanger for synthesis gas. The fifth and sixth chapters will finally describe the most recent research activities that led to both the experimentation of polymer filter bags for a commercial small-scale gasifier, and the investigation in the field of micro-algae for the realization of a syngas water scrubbing system aimed at eliminating the pollutants present therein. During the discussion, the critical issues and potentialities encountered in the use of the various syngas conditioning systems will be exposed. The definition of key thermo-fluid dynamic parameters will result in the simplification of the initial multiphase system, building a solid starting point for the continuous improvement of these technologies.


2020 - Scarti cerealicoli: una risorsa rinnovabile e sostenibile per il settore edilizio [Tesi di dottorato]
BARBIERI, VIRGINIA
abstract

Wheat is the most common type of cereal used worldwide and the production of wheat husk waste from the refinement process is estimated to ca. 10 million tons in 2020 only in the EU. Since now, no well-defined recycling strategy exists and natural decomposition with the consequent production of polluting greenhouse gases is often the final destination of these materials. Recycling of agricultural by-products, in particular in the building sector, have recently been in focus through many EU-funded project. However, wheat husk has not yet been investigated. Although current thermal insulation materials have excellent performances, they are generally based on petroleum-derived raw materials (e.g. extruded polystyrene, expanded polystyrene, polyurethane foam, etc.). So-called bio based building material are more environmental-friendly alternatives, the most common one available on the market being lime hemp concrete. This material contains hemp hurds as filler and hydrated and/or hydraulic lime as binder. The material has good thermal insulation properties (0.05-0.12 W/m*K) and excellent moisture buffering and acoustic properties. An alternative to lime-based binders, having the same or even better green value, are magnesia-based ones. The present work was aimed to the design of wheat husk insulating material as potential alternative to hemp lime concrete. The idea was to combine the necessity of finding valid recycling alternative for wheat husk with the need of the building sector for environmental-friendly insulation materials. The results from initial physical characterizations of wheat husk showed a low dry thermal conductivity (ca. 0.05 W/(m.K)), comparable to hemp hurd, as well as good hygric regulation performances (MBV equal to 2.06 g/(m2.%RH)). Hence, the material was considered a viable alternative as filler in biocomposites. In subsequent investigations, lime wheat husk concrete was prepared and compared to a lime hemp concrete. Despite the higher dry apparent density of the former, the total porosity (around 80%) and dry thermal conductivity (ca. 0.09 W/(m.K)) were similar for both types of concrete. The somewhat lower mechanical performance of lime wheat concrete (~0.20 MPa) with respect to lime hemp concrete (0.24 MPa), although in line with those expected for infilling walls without load bearing requirements, was found to be due to lower adherence of wheat husk to the lime-based binder. In order to obtain a material with improved mechanical performance, subsequent work was dedicated to investigated an alternative binder with better compatibility with the novel vegetal filler. In particular, a magnesia-based cementitious materials was investigated. Setting and hardening of the investigated system relied on hydration of reactive MgO in the presence of MgSO4 and a vegetal flour leading to a complex porous microstructure composed of needle-shaped magnesium oxy sulfate cement phases as well as magnesium hydroxide with carbon uptake potential. Wheat husk magnesia concrete and hemp hurd magnesia concrete were prepared and compared to the corresponding lime-based materials previously investigated. Mechanically stronger composites were obtained with magnesia-based binder. In addition, the best mechanical performance was observed for composites containing wheat husk as filler. Microstructural investigations showed that both lower porosity and stronger adhesion of wheat husk aggregate with the binder phase are responsible for the improved mechanical performance. Concluding, the results obtained during this PhD research showed that direct utilization, i.e. without any energy-consuming pre-treatments, of wheat husk for the production of bio based building materials intended for thermal insulation purposes is a viable recycling option and a valid alternative/substitute for less environmental-friendly traditional insulation materials.


2020 - Studio degli effetti giroscopici agenti su rotori sottoposti ad eccitazione parametrica periodica [Tesi di dottorato]
DE FELICE, ALESSANDRO
abstract

The dynamic analysis of torque-transmitting flexible rotors is a research subject of great interest in mechanics of machines, presently encouraged by a general increasing trend towards high speed rotating equipment in conjunction with higher power density. The effects of axial end thrust and twisting moment, representing common loading conditions in engineering applications, have long been investigated restricting the attention to the time-invariant problem. More recently, however, also oscillating load components have been considered, and studied as causes of parametrical excitation in rotor dynamics. The induced effects are potentially destabilizing, making the stability analysis of this specific kind of dynamic systems a problem of both theoretical interest and practical importance, which until now has not been satisfactorily studied in the literature. In this thesis some novel insights are first provided in the analysis of distributed parameter linearized models of high-speed power transmitting flexible rotors subjected to constant external loads. On this necessary basis, an analysis is then developed aimed at clarifying the gyroscopic effects on the stability of parametrically excited rotors, also highlighting the role played by damping distributions. As case-study, a balanced shaft is considered, modelled as a spinning Timoshenko beam loaded by oscillating axial end thrust and twisting moment, with possibility of carrying additional inertial elements. After discretization of the equations of motion into a set of coupled ordinary differential Mathieu-Hill equations, stability of Floquet-Lyapunov solutions is studied via eigen- problem formulation, obtained by applying the harmonic balance method. A numerical algorithm is then developed for computing global stability thresholds in presence of both gyroscopic and damping terms, aimed at reducing the computational load. Finally, the influence on stability of the main characteristic parameters of the rotor is analyzed with respect to frequency and amplitude of the external loads on stability charts in the form of Ince-Strutt diagrams. As a novel result, it is demonstrated that gyroscopic terms produce substantial differences in both critical solutions and stability thresholds: the former are generally non-periodic limited-amplitude functions, and modifications induced on stability thresholds consist of shifts and merging of unstable regions, depending on the separation of natural frequencies into pairs of forward and backward values induced by angular speed. As a practical result, the developed numerical algorithm provides an effective and efficient tool for tracing stability thresholds, also suitable for application to a more general category of gyroscopic systems, including complex shape rotors in those cases in which properly condensed finite element models would be available. The stability charts thus obtained can then be used as guidelines to provide simple safety limits for the time-varying, periodic loads acting on a rotor.


2020 - Studio numerico di flussi turbolenti in regime di convezione naturale e mista [Tesi di dottorato]
FREGNI, ANDREA
abstract

The aim of this work is to investigate turbulent flows and heat transfer phenomena where buoyancy forces are non-negligible. The studies are conducted by means of Direct Numerical Simulations performed in two configurations: a wall-bounded buoyancy-driven flow and a free-shear buoyancy-aided case. Calculations are conducted using a customised version of the open source code Incompact3d, where modifications include the addition of the Boussinesq's buoyancy term in the momentum equations and the implementation of an open outflow boundary condition suitable for buoyant and turbulent flows. In the text each novel implementation is presented together with a validation test. Firstly buoyancy-driven convection is investigated in the Rayleigh-Bénard cell employing different fluids: mercury (Pr=0.025), air (Pr=0.7) and water (Pr=7). Instead of the usual approach, where the Prandtl number is varied in constant-Rayleigh-number conditions, the three simulations are performed at constant Grashof number, Gr=Ra/Pr=5 x 10^7. This procedure allows the study of the Prandtl number influence while maintaining a constant ratio between the advective and diffusive terms in the momentum equations. The analysis of customarily and specifically developed statistics sheds light on the small-scale fluctuations and large-scale motions which are responsible for the energy transfer at different Prandtl numbers. Secondly, a non-canonical configuration which involves three planar jets vertically entering a pool with different temperature is studied. Beside the theoretical interest, this research is motivated by the study of temperature fluctuations induced by fuel rods cooling inside Liquid Metal Fast Reactors (LMFRs), which employ a liquid metal as coolant. This phenomenon is called thermal striping and might induce thermal-fatigue failures in the containment vessels. In order to infer on thermal striping the Prandtl number of Lead-Bismuth Eutectic at 220° C, i.e. a typical envisaged condition in LMFRs, is considered (Pr=0.031). Reynolds number is set to Re=5000 and the mixed convection regime is established at a Richardson number Ri=0.25. Results show that jets undergo an intense mixing close to their inlets, while at distances larger than ten times the jet width they are coalesced in a single and almost isothermal stream. Here the flow displays some of the self-similar properties observed in canonical planar jets. An original formulation of the Coandă effect reveals the mechanism underlying jets coalescence. Finally, fields of turbulent viscosity and diffusivity, as well as kinetic and thermal dissipations, show behaviours which are unlikely to be reproduced by typical eddy-viscosity turbulence models. In summary this study provides an original insight into the physics of turbulent heat transfer in wall-bounded and free-shear configurations where buoyancy forces are non-negligible. Results reported in this text might also be used for the development and validation of turbulence models to be employed in buoyant flows.


2020 - Sviluppo di metodologie a basso costo computazionale per l’integrazione della modellazione di proprietà chimiche di combustibili in simulazioni 3D-CFD di combustione e formazione di particolato in motori benzina a combustione interna [Tesi di dottorato]
DEL PECCHIA, MARCO
abstract

Nowadays, the leading driver pushing the technological development of the new era of internal combustion engines is the continuous strive for the increase of efficiency and emissions reduction. The increasing complexity of new combustion systems is made possible thanks to the evolution of 3D computational fluid dynamics models. At the same time, the introduction of new technical solutions pushed the in-cylinder combustion process to operate in challenging conditions which are particularly demanding under the modelling standpoint, considered the high degree of accuracy required. In this scenario, the integration of chemistry-based methodologies in 3D computational fluid dynamics simulations is a powerful tool to quantitatively estimate the underlying phenomena linked to fuel chemistry which are responsible for the local mixture reactivity and, in turn, for the evolution of the combustion process. For example, the correct estimation of combustion-relevant fuel properties such as laminar flame speed, ignition delay and sooting tendency is a key factor to model, respectively, the flame propagating characteristics, the end-gas reactivity and soot emission formation in gasoline engines. The need for a quantitative estimation of the aforementioned phenomena has recently promoted a widespread use of methodologies aiming to directly solve chemistry at a cell-wise level in the computational grid. While the main advantage of this approach is the possibility to directly solve chemistry cell by cell, its main drawback is the non-negligible increase in computational cost. In the present work, a comprehensive methodology is developed to integrate detailed chemistry-based information in in-cylinder simulations retaining a high chemistry-fidelity at a feasible computational cost for the automotive industry standard. In particular, dedicated methodologies are proposed to model the flame propagating characteristics, the auto-ignition characteristics, the sooting tendency and the main chemico-physical properties of gasoline at thermodynamic and mixture quality conditions typically experienced in current production gasoline direct injection engines. All the proposed methodologies rely on detailed off-line chemistry-based simulations, carried out in a chemistry solver, to quantitatively estimate the aforementioned properties. This approach is validated on a optically-accessible gasoline direct-injection research engine on different injection strategies at a full-load operating point, with a particular focus on soot engine-out emissions. Due to the increasing limitations imposed on particulate matter by the current regulations worldwide, accurate CFD-based methodologies are needed to predict soot formation in gasoline direct engines. Therefore, a customized version of the Sectional Method model, based on a tabulated constant pressure reactors approach, is used in 3D CFD simulations for this purpose. The predictive capabilities of the proposed chemistry-based comprehensive methodology is proved twice. Firstly, the improved description of the combustion process development is validated thanks to in-cylinder flame front propagation visualizations. In the second place, an experimental-CFD comparison, in terms of engine-out Particulate Mass, Particulate Number and Particle Size Distribution Function, proves the capability of the proposed methodology, not only to describe the dependence of the sooting tendency on the injection strategy, but also to quantitatively predict soot characteristic quantities at the exhaust with a good agreement.


2020 - Sviluppo di un sistema ad alta risoluzione spaziale per la previsione della qualità dell'aria urbana tramite approccio modellistico multi-scala e sua applicazione alla città di Modena [Tesi di dottorato]
VERATTI, GIORGIO
abstract

In Europe, emissions of many air pollutants have decreased substantially over the past decades, resulting in improved air quality across the region. However, air pollutant concentrations are still too high, and air quality problems persist. The Po Valley, located in the northern part of Italy, is one of the most critical area of the country in terms of pollution level. The reason to this problem is not only related to the high population density with its related activities, but it is also due to the orographic conformation of the territory which appears surrounded by mountains on three sides: the Alps to the west and to the north and the Apennines to the south. These geographical characteristics lead to meteorological conditions unfavorable to the atmospheric dispersion: average annual wind speed less than 2 m s-1, recurrent thermal inversions at low altitude, low mixing layer heights and persistent foggy and hazy events during winter time. One of the main critical air pollutants in terms of health effects is nitrogen dioxide (NO2), whose levels in the last years exceeded national and WHO (World Health Organization) standards in many urban areas across the Po Valley, exposing urban population to the risk of pollution-related diseases and health conditions. The main goal of this study was to develop a multi-scale modelling system able to provide hourly NOx (NO + NO2) concentration fields at a building-resolving scale in the urban area of Modena, a city in the middle of the Po Valley, in order to support environmental policies, epidemiological studies and urban mobility planning. The modelling system relied on two different models: the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem), which is able to compute concentration fields over regional domain by considering specific emission scenarios, and the Parallel Micro SWIFT and SPRAY (PMSS) modelling suite accounting for dispersion phenomena within the urban area. The PMSS modelling suite was used to simulate at building-scale resolution the NOx dispersion produced by urban traffic flows in the city of Modena. Conversely, the WRF-Chem model was selected to estimate the NOx background concentrations on multiple domains with a nesting technique, in order to take into account emissions both at regional and local scale by excluding traffic emissions sources over the city of Modena. In the first part of the work the modelling system was performed for the period between 28 October and 8 November 2016, the same period whereby a direct vehicle flow measurement campaign was carried out continuously with 4 Doppler radar counters in a four-lane road in Modena, in order to reproduce emission hourly modulation rates. In second section of the study the modelling system was set-up with the aim of produce hourly forecast of NO2 and NO concentrations, up to one day ahead, for the city of Modena for the entire month of February 2019. Simulated and observed hourly concentrations exhibited a large agreement in particular for urban traffic site where detailed traffic emission estimations proved to be very successful in reproducing the observed trend. At urban background stations, despite a general underestimation of the observed concentrations, the combination of WRF-Chem with PMSS provided daily pattern in line with observations. Finally, the statistical analysis showed that PMSS combined with WRF-Chem at both traffic and background sites fulfilled standard acceptance criteria for urban dispersion model evaluation, confirming that the proposed multi-modelling system can be employed as a tool to support human exposures and health impact assessments as well as the effects of local traffic policies on urban air quality.


2020 - Un’architettura innovativa per Power Unit ibride per veicoli di piccole dimensioni: progettazione, analisi, produzione e sperimentazione [Tesi di dottorato]
MANGERUGA, VALERIO
abstract

This thesis presents the development of a hybrid power-unit starting from a small engine derived from a motorcycle application. In particular, the system is made up of a brand new, single-cylinder 480 cc internal combustion engine developed on the basis of the Ducati “959 Superquadro” V90 2-cylinders engine. The thermal engine is assisted by a custom electric motor (30 kW), powered by a Li-Ion battery pack. The Ducati “959 Superquadro” engine is chosen because of its high power-to-weight ratio, and for taking advantage of its V90 2-cylinder layout. In fact, the vertical engine head is removed and it is replaced by the electric motor directly engaged to the crankshaft using the original valvetrain transmission chain, thus achieving a very compact package. This solution is suitable for many V-type engines and aims to obtain a small hybrid power unit, leaving the way open for possible motorcycle/small vehicle applications. The resulting internal combustion engine of this project is a single cylinder engine which would result to be unbalanced if compared to the original V90 configuration. For this reason, several unconventional balancing systems are investigated. In particular, one of the solutions consists in replacing the unused piston with a balancer rod obtaining an articulated quadrilateral mechanism. This solution allows to reduce the friction losses and to specially drop off the pumping losses. Parallelly, the possibility of keeping the original piston is considered which definitely represents a less invasive solution but determines a certain power loss due to both friction and pumping. The mechanical behaviour of the original chain is investigated performing a dynamic analysis of the whole crank mechanism. In particular, the twin cylinder model considering the original valvetrain system is compared with the single cylinder model engaged with the electric motor, in order to assess the possibility to use the chain for this specific purpose. A specific electric motor case is designed and manufactured via Additive Manufacturing technology, in order to include the chain housing, the electric motor cooling system and the lubricating system. Furthermore, the case flange is designed to perfectly fit with the original engine deck in order to allow the engine cooling circuit to match with the electric motor one. Specifically, a thermo-structural analysis is performed in order to assess the mechanical strength of the electric motor case. The output power and size of the electric motor are estimated developing a spreadsheet which considers the power dissipated by the vehicle taking into account the mass of the car, the rolling resistance, the drag force and the lift force. Moreover, the maximum amount of energy needed is calculated thus allowing the capacity of the battery to be determined. In particular, the model allows the best operating point for both the electric motor and the internal combustion engine to be identified. Several strategies are developed concerning the power split during different operating cycles and taking into account the vehicle performance, the fuel consumption and the electric energy consumption. Finally, a first prototype of the developed power-unit is manufactured and tested at the bench test thus providing useful experimental data for the validation of the different numerical models employed.


2020 - UN’INDAGINE SULLA VARIABILITA’ CICLICA NEI MOTORI A COMBUSTIONE INTERNA UTILIZZANDO PROPER ORTHOGONAL DECOMPOSITION E LARGE-EDDY SIMULATIONS [Tesi di dottorato]
RULLI, FEDERICO
abstract

The main goal of research on reciprocating internal combustion engines (ICEs) consists in increasing the power output while reducing pollutant emission and fuel consumption. Cycle-to-cycle variability (CCV) is closely coupled with the intrinsic turbulent nature of in-cylinder flow and is detrimental in terms of combustion efficiency, fuel consumption, and tailpipe emissions. Due to fluctuations in flame propagation, heat release, and burnt product formation, CCV is now seen as one of the major limiting factors for higher power output and lower fuel consumption in ICEs. Therefore, it is essential to understand and control CCV to improve the overall engine efficiency and performance. Experimental techniques like particle image velocimetry (PIV) provide a powerful technical support for the analysis of the spatial and temporal evolution of the flow field in ICEs. Proper orthogonal decomposition (POD) has been largely used in conjunction with PIV to analyze flow field characteristics. Several methods involving POD have been proposed in the recent years to analyze engine CCV. In this work, phase invariant POD analysis, conditional averaging, and triple and quadruple POD decomposition methods are introduced and applied to a large database of PIV data from the optically accessible TCC-III research engine. Results are discussed with particular emphasis on the capability of the methods to perform both quantitative and qualitative evaluations on CCV. A new quadruple POD decomposition methodology is proposed and compared to those available in the literature. Besides experimental techniques, Computational Fluid Dynamics (CFD) has become a fundamental tool for understanding the complex aero-thermochemical processes that take place in the cylinder and for driving the development of new technological solutions. Large-eddy simulation (LES) is the most practical simulation tool to understand the nature of CCV. This work investigates the CFD capabilities to simulate CCV. Several methods of analysis were assessed on a 50 LES cycles dataset on the TCC-III engine under motored conditions. The accuracy and the reliability of CFD simulations stands in the models used for the discretization of the fluid domain and for the numerical computation of the governing equations. The meshing strategy plays a central role in the computational efficiency, in the management of the moving components of the engine and in the accuracy of results. The overset mesh approach, usually referred to as Chimera grid or Composite grid, was rarely applied to the simulation of ICEs, mainly because of the difficulty in adapting the technique to the specific complexities of ICE flows. This work demonstrates the feasibility and the effectiveness of the overset mesh technique application to ICEs thanks to a purposely designed meshing approach. 50 LES cycles were performed on the TCC-III engine under motored conditions. The proposed POD quadruple decomposition methodology was extensively applied to assess both the accuracy of the simulated results and the potential of the method itself for understanding CCV.


2019 - Compression ratios comparison between engines operating with producer gas [Relazione in Atti di Convegno]
Mason, J.; Kaufmann, B.; Tartarini, P.; Puglia, M.; Morselli, N.; Veratti, G.; Bigi, A.
abstract


2019 - Hybridization of solar power plants with biogas from anaerobic digestion: A modeled case study [Relazione in Atti di Convegno]
Pedrazzi, S.; Masetti, F.; Allesina, G.; Tartarini, P.
abstract

This work shows the numerical simulation of a hybrid renewable power plant composed of a Concentrated Solar Plant (CSP) with molten salt storage sub-system, a Rankine steam cycle power plant and a biomass anaerobic digester. Biogas produced by the digester is used as fuel in the boiler of the steam cycle coupled with methane. "Greenius" software has been used to simulate the CSP system aimed to satisfy an electrical power demand of the city Messaad, Algeria. Results concerning electrical energy produced, biogas and methane consumption was used with CAPEX and OPEX costs of the plant to calculate the Levelized Cost of the Electrical energy produced (LCoE). Several simulation were done varying the size of the solar field and of the thermal storage in order to find the compromise configuration with an high renewable energy production, a low methane consumption and a low LCOE. Simulations show that the CSP configuration with 2.07 of Solar Multiple (SM) and 9 of Full Load Hour (FLH) result in a low LCOE value (97.32 €/MWh), high annual system efficiency (11.51%), low methane share (8.73%) and low dumped heat ratio (10.22%).


2019 - Modeling and optimization of industrial internal combustion engines running on Diesel/syngas blends [Articolo su rivista]
Rinaldini, Carlo Alberto; Allesina, Giulio; Pedrazzi, Simone; Mattarelli, Enrico; Tartarini, Paolo
abstract

The paper presents a numerical analysis of combustion, carried out on a compression ignition indirect injection engine fueled by both Diesel and syngas, the latter obtained from biomass gasification and introduced in the intake manifold. The computational fluid dynamics model includes an improved chemical kinetics scheme, tailored on the syngas-diesel dual fuel combustion. The model was validated by an experimental campaign, on the same engine. The syngas fuel was produced by a small scale gasifier running on wood chips. Several simulations were performed varying both the share of syngas and the Diesel start of injection angle. The total amount of heat released by combustion can increase up to 50%, along with the indicated work and the cylinder peak pressure. The start of injection angle should be modified in order to preserve the mechanical integrity of the engine, as well as to maximize its brake efficiency. The numerical analysis provides the guidelines for setting the injection strategy, as a function of the syngas share.


2019 - Passive system for internal surface cleaning and homogenization in the air-lift vertical column photobioreactors [Relazione in Atti di Convegno]
Morselli, N.; Altunoz, M.; Puglia, M.; Arru, L.; Tartarini, P.
abstract

the mixing and surface cleaning performances of an air-water diffuser is tested in a 70 L air-lift bubble column photobioreactor in which single-celled Cyanobacteria Synechocystis sp. fed by sewage sludge waste is cultivated. Results have shown that a water velocity of 0.2 ms-1 in the non-aerated bottom part of the PBR and 0.06 ms-1 in the aerated zone are sufficient to prevent sludge deposition and biofouling on the surfaces. Moreover, water recirculation is observed to have an important role on the sludge mixing and algal homogenization of the photobioreactor. A computational model is then created and tuned using experimental data in order to predict the water and air velocity map in the whole domain.


2019 - Results of the two-year rebaf project: How to exploit biomass from river maintenance [Relazione in Atti di Convegno]
Pedrazzi, S.; Morselli, N.; Puglia, M.; Barbieri, L.; Lancellotti, I.; Andreola, F.; Malcevschi, A.; Giorgini, L.; Ceotto, E.; Tartarini, P.
abstract

This paper discusses activities and results of the REBAF project: a two-year Italian regional research project focused on the energy conversion of biomass residues from river, canals and basins maintenance activities. Innovative pathways for the exploitation of grass and woodsy biomasses were investigated. Gasification and pyrolysis are the key technologies for biomass conversion into energy. Woodsy biomass was tested as fuel in a small scale commercial gasification power plants that produce heat and power using a IC engine. A valuable by-product of the process was biochar. This was tested as soil improver in giant reed crop parcels and a sensible increase of dry biomass production was achieved in comparison with control parcels. The grass residues obtained from canals maintenance were carbonized in lab-scale pyrolyzer at a temperature of about 450 °C through the hot exhaust of the engine fueled by the gasifier. The pyrolysis gases were used directly in the gasifier in substitution of the gasifying agent. The residual carbon afterward the pyrolysis process was used as filler in cements, plasters and polyurethane panels increasing performance of these building materials.


2019 - Spent Coffee Grounds in the Production of Lightweight Clay Ceramic Aggregates in View of Urban and Agricultural Sustainable Development [Articolo su rivista]
ANDREOLA, Nora Maria; Borghi, Alessandro; PEDRAZZI, Simone; ALLESINA, GIULIO; TARTARINI, Paolo; LANCELLOTTI, Isabella; BARBIERI, Luisa
abstract

This paper presents an innovative application for spent coffee grounds (SCGs) used as filler for the formulation of lightweight clay ceramic aggregates (LWA). LWA can be used for urban and agricultural purposes as a sustainable solution. Spent coffee grounds were tested as a pore forming agent partially acting as a replacement for red clay in material formulation before firing. Substitutions of 10, 15, and 20 wt.% of red clay were tested. The properties of lightweight aggregates with 15 wt.% of SCGs were improved using a specifically tailored fertilizer glass due to its low pH and conductivity within the soil tolerance range. Packaging glassy sand, cattle-bone flour ash, and potassium carbonate were mixed and melted in order to obtain this glass, which when added to the clayey batch functionalized the aggregates by phosphorus and potassium nutrients. The results (in particular, porosity and bulk density) show that the lightweight aggregates obtained have interesting properties for possible uses both in urban (e.g., green roofs as a drainage layer) and agricultural purposes. Moreover, pH and conductivity are in line with the Italian Standard regarding soil amendment (D.lgs. 75/2010). In addition, several leaching tests were performed in a solution containing 2 vol.% citric acid (C6H8O7) to evaluate the release capacity not only of nutrients (P and K)mbut also to check the presence and release of heavy metals, such as lead (Pb), that may come from the glassy precursor. The results obtained showed that nutrients are effciently released in 21 days (P = 87.73% and K = 25.74% of released percentage) and Pb release is under the standard threshold of 30 ppm.


2019 - Study of copper content distribution through the thermochemical conversion chain of vine pruning biomass [Relazione in Atti di Convegno]
Santunione, Giulia; Bigi, Alessandro; Puglia, Marco; Morselli, Nicolò; Sebastianelli, Lorenzo; Tartarini, Paolo
abstract

Viticulture is mostly affected by a continuous use of copper-based fungicides to contrast fungal diseases. This treatment, used in both traditional and organic cultures, results in a considerable accumulation of Cu in the top soil, then into plants and soil biota. Furthermore, Copper tends to migrate into air, water and soil ecosystem, posing serious threats to the environment and human health because of its toxicity. At the same time, vineyard pruning represent a valiant woody biomass source for renewable energy production through gasification, the thermochemical process where carbonaceous material is converted into a gaseous flammable fuel called syngas. Currently, one of the important challenges for bioenergy production through gasification is the management of heavy metal-contaminated biomasses used as fuel. This study is aimed to investigate the distribution of copper through thermochemical conversion chain of wood grape, from biomass to electrical and thermal energy production. Starting to the amount of Cu based fertilizers applied to traditional and organic viticulture, the heavy metal residues have been checked and analyzed into ashes biomass derived, into gas emissions coming out from PP20 gasifier and into biochar as gasification process by-product. Inductively coupled plasma mass spectrometry (ICP-MS), and X-ray Fluorescence spectroscopy (XRF) methods have been performed in order to quantify the amount of residual Copper into the different tested arrays. The assessment of Cu persistence along the thermochemical treatment chain of grape biomass is provided. © 2019 ETA-Florence Renewable Energies.


2019 - Use of fabric filters for syngas dry filtration in small-scale gasification power systems [Relazione in Atti di Convegno]
Morselli, N.; Parenti, M.; Puglia, M.; Tartarini, P.
abstract

This work focused on the assessment of the wood gas filtrating performances of fabric filter bags applied to a small-scale commercial gasification power plant by All Power Labs. As known, the raw producer gas contains pollutants such as tars and particulate matter that need to be removed in order to avoid the premature failure of the mechanical parts of the facility and of the internal combustion engine. PTFE-coated and felt bags were tested to assess their response to the tars and water vapors condensation, in terms of pressure drop. The results shown on one hand the tendency of felt bags to be more sensible to condensation phenomena and on the other hand the drawback of PTFE bags to generate higher pressure drop since the beginning. The possibility of pre-coating the felt bags with fine biochar generated from the gasification facility was then tested. Tars and soot gravimetric analyses conducted on wood gas samples shown the ineffectiveness of pre-coating using char and the coherent tendency of felt bags to increase the filtration performances over time.


2019 - Use of light scattering for online detection of tar and particulate matter from biomass gasification [Relazione in Atti di Convegno]
Allesina, G.; Pedrazzi, S.; Rogak, S.; Grace, J. R.; Tartarini, P.
abstract

Gasification is one of the most promising technology for an efficient use of biomass fuels. A gate-keeper issue that is holding this technology from being widely used is gas conditioning. All gasifiers architecture suffer in some degree due to tar and particulate content in the gas stream. Depending on the final application, different level of pollutant may preclude a specific use. The cleaning level is more and more relevant moving from IC engines to gas turbine or fuel cells. For this reason this work want to explore an on-line method for tar and particulate detecting using a light scattering system. The proposed solution is based on a dual stage gas dilution combined with the use of a commercial air monitoring device.


2019 - Zero-waste approach for combined energy and fertilizer production: The case of Ravenna, Italy [Relazione in Atti di Convegno]
Baniasadi, M.; Santunione, G.; Moradi, A.; Tartarini, P.
abstract

There is a need to find a solution to solve the problem of increasing agricultural practices which can lower the pressure on soil. Application of compost or biochar to the soil is proved to be a suitable solution to counteract this problem. Mixed application of these two products is even more sustainable environmental solution due to its effectiveness in the long-term carbon preservation. The biochar can be produced through gasification of municipal waste as a method for renewable energy production. This makes a new market for the unused biomass which is currently incinerated or landfilled. This paper summarizes the technical and economic aspect of system innovation toward utilizing organic and green waste for composting and energy production via gasification and application of the products (compost and biochar) for soil amendment, considering the case of Ravenna city in Italy. The municipal statistic data on waste management were used for this purpose. Gasification experiment of green waste for electricity production was performed in an open-top gasifier. The obtained results showed that the available waste in Ravenna could be used for production of large portion of energy consumption and at the same time provide biochar and compost mixture to be used in 700 hectare/y of the agricultural land in Ravenna. Moreover, the available methods and conditions in literature for mixing of biochar and compost were reviewed. The related European directives were also discussed.


2018 - Carbonization of residual biomass from river maintenance using waste heat from gasification power plants [Relazione in Atti di Convegno]
Puglia, Marco; Pedrazzi, Simone; Allesina, Giulio; Morselli, Nicolò; Tartarini, Paolo
abstract

This work follows the study presented in Stockholm at the 2017th EUBCE titled: “The Energetic Recover of Biomass from River Maintenance: the REBAF Project”. This previous work focused on the multidisciplinary approach to river maintenance in order to create more resilient systems together with the production of renewable energy. One of the outputs of the preliminary work presented was the distinction of the biomass from river maintenance into two major groups: suitable for gasification and not suitable for gasification. It was necessary to determine suitable and sustainable solutions for the energy recovery of both these groups. The final idea is discussed in this work, it consists in having an integrated system as depicted in Figure 2. The gasifier-engine system is fed with the higher quality biomass; it provides electrical power and hot exhaust gases that are used for the pyrolysis of the low-quality feedstock. The purpose of the pyrolysis reactor is to produce biochar to be used together with clay and other aggregates to produce highly porous, carbon negative, building materials. In this work a prototype reactor was assembled and tested using herbaceous biomass. Several configurations, in terms of exhaust gas temperature and biomass residence time were tested. Results showed the capability of coupling gasification and pyrolysis into integrated systems to increase the overall sustainability of the processes. On the other hand, char quality is strongly affected by the way this interaction is performed due to the quick cool down of the exhaust gases when the connection lines are not properly insulated.


2018 - Chemically enhanced char for syngas filtering purposes [Relazione in Atti di Convegno]
Pedrazzi, S.; Allesina, G.; Sebastianelli, L.; Puglia, M.; Morselli, N.; Tartarini, P.
abstract

This paper investigates the performance of gasification char as syngas filter medium. Char obtained from a small-scale downdraft gasifier was analyzed and chemically enhanced through an acid treatment using a sulfuric acid solution in a thermostatic bath at 40 °C. The treated char presents a higher BET value of 465.9557 m2/g in comparison with the untreated sample which has a BET value of 394.4430 m2/g. However, the treated sample has a low metallic cations content (K, Fe and Sr) and consequentially a low ash content compared to the untreated sampled. Char samples are used as cartridge filter media in order to assess their tar adsorption potential using a modified “Tar Sampling Protocol” method. Experimental results show a noticeable tar content reduction in the syngas using char as filter, in fact the treated char reduces the tar number from 1456 mg/Nm3 to 267.2 mg/Nm3 and the untreated char reduces the tar number from 1456 mg/Nm3 to 179.6 mg/Nm3. The difference in the tar adsorption is probably given by the char ash content that it is less in the treated sample.


2018 - Effects of load variation and purge cycles on the efficiency of Polymer Electrolyte Membrane Fuel Cells for stationary applications [Articolo su rivista]
Santangelo, Paolo Emilio; Tartarini, Paolo
abstract

Polymer Electrolyte Membrane Fuel Cells have become rather popular for power generation; Dead-Ended Anode design is currently adopted to limit hydrogen consumption. However, gas and water accumulation at the anode outlet decrease stack performance, and so, purges are carried out to remove them. This work focuses on a Polymer Electrolyte Membrane Fuel Cell system featuring a voltage-drop-based purging strategy; 4 electric-load conditions (0.6-1.8 kW) were imposed to evaluate how purges impact the system performance as the applied load varies. Long-duration experimental tests were conducted at a constant load to reproduce cycles typical of stationary applications; various electric, thermal, and transport parameters were measured, and efficiency was ultimately determined. An analogy between increasing the applied load and increasing the cathode-air humidity level was found in terms of purge-related hydrogen losses and purge time. Stack current intensity is not affected remarkably by purging, whereas stack voltage exhibits higher oscillations at the higher loads and is less stable at the lowest one. A relationship is suggested between voltage, anode stoichiometry, and stack temperature, especially over the initial transient trend prior to reaching an approximately steady condition. Overall stack efficiency decreases as polarization losses increase along with the applied load; fuel efficiency is almost constant, even though slightly bigger at the higher loads, which implies that lower fractions of hydrogen are lost during purges. Net efficiency is relatively flat over the operative range, so this purging strategy tends to counterbalance the effects of polarization losses. However, power used to sustain auxiliaries shows a bigger impact than purge-related energy losses.


2018 - Energy production and carbon sequestration in wet areas of Emilia Romagna region, the role of Arundo Donax [Articolo su rivista]
Allesina, Giulio; Pedrazzi, Simone; Ginaldi, Fabrizio; Cappelli, Giovanni A.; Puglia, Marco; Morselli, Nicolò; Tartarini, Paolo
abstract

This work investigated the utilization of giant reed as energy crop applied marginal areas of the municipality cluster "Unione Terre d'Argine" (UTA), Northern Italy. On one hand, the researchers modeled the giant reed productivity in terms of ton/year for each town of the cluster. They focused on those areas neighboring the local rivers and channels kept unused for farming activities: i.e. riverbanks or detention basin shores. On the other hand, experimental tests were performed to determine the behavior of giant reed as fuel in pilotscale gasification power plants. Results showed the high potential of small or pilot-scale gasifiers to increase the sustainability of river maintenance operations. From its gasification it is possible to produce electrical power together with biochar. Biochar is a powerful soil amendment that can be used straight in the riverbanks. The tandem process between giant reed growth and its gasification leads to 150 kg of CO2 sequestered for every ton of giant reed processed. Furthermore, the energy production from waste biomasses will help to perform better and more regular maintenance operation to the local rivers and channels, thus reducing the negative effects of possible floods.


2018 - Experimental and numerical analysis of thermal interaction between two droplets in spray cooling of heated surfaces [Articolo su rivista]
Santangelo, Paolo Emilio; Corticelli, Mauro Alessandro; Tartarini, Paolo
abstract

Dropwise cooling is a subject of interest for numerous industrial applications, which fosters fundamental research on the related mechanisms. The present work is focused on studying the cooling effect of 2 water droplets gently released onto a heated solid surface. The nominal initial temperature of the substrate was lower than 100 °C, thereby referring to evaporation regime. Heat-transfer phenomena were analyzed by an experimental and numerical approach at the solid/liquid interface and over non-wetted regions, thus evaluating mutual interaction between droplets. Infrared thermography was employed in a facility built to measure surface temperature from below through a fully non-intrusive approach. An infrared-transparent disk served as the substrate; its black-painted upper surface allowed heating and droplet deposition to occur on a blackbody. A numerical code was developed to model heat transfer within all bodies and at all interfaces by the finite-volume discretization method. Numerical results showed very good agreement with experimental temperature profiles and heat-flux distribution was predicted over the whole sampling region. Cooling effect was determined quantitatively together with the extent of the mutual-interaction region, where the influence of 2 sequentially-released droplets was proved higher and longer than that of a single-droplet configuration with the same amount of deposited water.


2018 - Gasification and wine industry: Report on the use vine pruning as fuel in small -scale gasifiers [Relazione in Atti di Convegno]
Allesina, Giulio; Pedrazzi, Simone; Puglia, Marco; Morselli, Nicolò; Allegretti, Francesco; Tartarini, Paolo
abstract

Ten different types of vine prunings were tested in a small-scale commercial gasifier produced by the All Power Labs. The specific consumption of the wood biomass power plant was measured for each type of biomass showing results from 0.92 to 1.32 kg/kWh. Syngas analyses and HHV calculation showed results higher than the reference calculated value from the gasification of typical wood biomass. On the other hand, the feeding operations resulted more complicated, here vine prunings are more likely to create bridging problems.


2018 - GASIFICATION OF BIOMASS FROM RIVER MAINTENANCE AND CHAR APPLICATION IN BUILDING MATERIALS PRODUCTION [Articolo su rivista]
Vezzali, Vittorio; Andreola, Nora Maria; Barbieri, Luisa; Lancellotti, Isabella; Pozzi, Paolo; Allesina, Giulio; Pedrazzi, Simone; Tartarini, Paolo
abstract

This paper exposes the research activities regarding REBAF (Energetic Recover of River Biomasses) project, focused on the maintenance operations self-sustainability of the Secchia river (Italy). Poplar was found as the most abundant and representative wood plant of Secchia riverbanks, with a good behavior during gasification process: from 1 hectare of maintenance every three year, it was possible to produce 23 MWh of electrical power and 31 MWh of thermal power. The biochar obtained was characterized and mixed with local red clay to create both lightweight aggregates (LWAs) for green roofs applications and bricks. Ashes coming from the gasifier cyclone were characterized and used to create bricks. The aims are the saving of raw materials and the obtaining of weight-lightened products with high porosity. Biochar and ashes were found to be suitable for this purpose given their organic carbonaceous nature, according to X-ray diffractometry, Loss on Ignition (LOI) and TG-DTA results. Application on LWAs by substituting 15%wt of the clay with biochar leads to a weight-lightening of the material. To optimize LWAs pH, spent coffee grounds (SCG) were added with proportion of 85% clay-15% biochar/SCG. A greater decrease in weight and pH values in the neutrality range were observed. Adding 20%wt biochar or ashes on bricks led to a significant reduction of materials bulk density (from 2 to 1.5 g/cm3) and the achievement of 40-45% porosity. With higher additions (until 40%wt) bulk density gets lower (1.2 g/cm3–1.3 g/cm3), but the material results weaker with a worst mechanical strength.


2018 - Gasification of cotton crop residues for combined power and biochar production in Mozambique [Articolo su rivista]
Allesina, Giulio; Pedrazzi, Simone; Allegretti, Francesco; Morselli, Nicolò; Puglia, Marco; Santunione, Giulia; Tartarini, Paolo
abstract

Cotton agricultural industry is an important sector for some developing countries, whose energy consumption is dramatically rising. Here, biomass is the most important source of energy, but they are used in an inefficient way, causing atmospheric pollution and wasting resources. Combined energy generation and biochar production using cotton residues briquettes as fuel in a PP20 gasifier plant is investigated. The machine has demonstrated similar performances to its “conventional” use: 14% global efficiency and 1.16 kg/kWhelspecific consumption of cotton briquettes are observed. It is calculated that one-hectare field can generate more than 4 MWh and about 130 kg of biochar per year. Biochar represents a valuable by-product; if used as amendment for cotton growth it can improve the soil conditions, both decreasing the need of fertilizers up to 50%. A circular economic model based on cotton waste gasification is proposed. Clean and affordable energy can be produced, in order to promote a sustainable development of rural areas.


2018 - Use of gasification char for hot gas filtration in micro-scale power plants [Relazione in Atti di Convegno]
Morselli, Nicolò; Allesina, Giulio; Pedrazzi, Simone; Puglia, Marco; Mason, James; Lemberger, Adrienne; Tartarini, Paolo
abstract

Char is a carbonaceous gasification by-product often used as soil amendment due to its high porosity and recalcitrant structure. Porosity is a fundamental feature when char is used to adsorb liquids and aerosol. This paper investigates gasification char as filtering medium for producer gas in small-scale gasifiers. Two metallic candle filters filled with about 1 kg of gasification char each were fabricated and tested under different temperature conditions (60, 70 to 80 °C). Char behavior as tar and particulate filter is qualitative and quantitative assessed evaluating tar deposits afterwards the engine governor as well as using the “Tar Sampling Procedure” methodology. Encouraging performance of char candle filters was achieved with a producer gas temperature of 60 °C and with gas-air mixture temperature of 70 °C at the engine manifold. Furthermore pressure drop across the filters was monitored and its influence on the engine maximum power output was evaluated.


2017 - Combined Effects of LED Lights and chicken manure on Neochloris oleoabundans Growth [Articolo su rivista]
Altunoz Hatipoglu, Meltem; Pirrotta, Onofrio; Forti, Luca; Allesina, Giulio; Pedrazzi, Simone; Obali, Olcay; Tartarini, Paolo; Arru, Laura
abstract

In this study a photobioreactor prototype is presented for the culture growth of microalgae model organism Neochloris oleoabundans by using chicken manure waste as feedstock along with the optimum combination of led light wavelengths and light intensity. Particularly interesting results are observed on the strains fed by chicken manure medium under the proper combination of red and blue LED light illumination, the microalgal growth resulted comparable with the strains fed by the costly commercial microalgal growth medium (BG 11 medium). Cell concentration, optical density, growth rate, cell size, total lipid and photosynthetic pigment content have been monitored during a time-course experiment. The data suggest that there are difficulties due to white light diffusion into the dark chicken medium, which leads to a generally lower intensity scattered along all wavelengths; blue or combined red and blue lights resulted in a higher irradiation density, affecting microalgae cell growth.


2017 - Control and suppression of sauna fires by water-mist systems [Relazione in Atti di Convegno]
Santangelo, Paolo Emilio; Tarozzi, Luca; Tartarini, Paolo
abstract

Saunas are currently included in many facilities and require dedicated fire-protection systems, since short circuits and direct contact with incandescent materials may start a fire involving timber, fabric and chemicals. In this frame, assessing the capabilities of water mist is the major scope of the present work. A real-scale setup was built and equipped with thermocouples and a hot-plate thermometer to evaluate control and suppression performance. Timber benches were inserted and the fire was initiated in a wood crib. The system successfully controlled and contained the fire, as the bench damage ratio was always kept below 5%. However, extinction was not achieved in 2 cases and notably in the supposed most challenging configuration in terms of ventilation, initial room temperature and nozzle-to-wall distance. On the other hand, ignition-source location, wood-crib damage ratio and air-gap between benches and walls did not affect suppression performance.


2017 - Dynamic behavior investigation of a micro biomass CHP system for residential use [Articolo su rivista]
Malaguti, Vania; Lodi, Chiara; Sassatelli, Matteo; Pedrazzi, Simone; Allesina, Giulio; Tartarini, Paolo
abstract

Aim of this work is to define a dynamic model developed in the Trnsys software environment where a biomass boiler and two micro-CHP gasifiers are considered as heat source for a detached house. The selected case study is a detached house of about 240 m2near Bologna, Northern Italy, where the HVAC system is currently equipped with a diesel oil boiler with 40 kW of thermal power. The building is connected to a farm and the total electrical consumption is about 13850 kWh/year. The thermal energy demand was calculated and validated in Trnsys using measured diesel oil consumption data. Two different retrofitting solutions for the heating system have been investigated: biomass boiler and micro-CHP gasifiers. Results show the capability to use biomass boiler and micro-scale gasifiers as heat source for the building with a wood consumption of 23 and 86 ton/year respectively. The gasifier electricity production is greater than the electrical demand and an extra energy of 64800 kWh/year is injected into the grid. The cost-benefits economical assessment of these retrofitting solutions is reported considering subsidies for renewable energy production.


2017 - Experimental investigation on a Common Rail Diesel engine partially fuelled by syngas [Articolo su rivista]
Rinaldini, Carlo Alberto; Allesina, Giulio; Pedrazzi, Simone; Mattarelli, Enrico; Savioli, Tommaso; Morselli, Nicolo'; Puglia, Marco; Tartarini, Paolo
abstract

The high efficiency, reliability and flexibility of modern passenger car Diesel engines makes these power units quite attractive for steady power plants totally or partially running on fuels derived from biomass, in particular on syngas. The engine cost, which is obviously higher than that of current industrial engines, may not be a big obstacle, provided that the re-engineering work is limited and that performance and efficiency are enhanced. The goal of this work is to explore the potential of a current automotive turbocharged Diesel engine running on both Diesel fuel and syngas, by means of a comprehensive experimental investigation focused on the combustion process. The engine is operated at the most typical speed employed in steady power plants (3000 rpm), considering three different loads (50–100–300 Nm/16–31–94 kW). For each operating condition, the syngas rate is progressively increased until it provides a maximum heating power of 85 kW, while contemporarily reducing the amount of injected Diesel oil. Maximum care is applied to guarantee a constant quality of the syngas flow throughout the tests, as well as to maintain the same engine control parameters, in particular the boost pressure. It is found that in-cylinder pressure traces do not change very much, even when drastically reducing the amount of Diesel fuel: this is a very encouraging result, because it demonstrates that there is no need to radically modify the standard stock engine design. Another promising outcome is the slight but consistent enhancement of the engine brake efficiency: the use of syngas not only reduces the consumption of Diesel oil, but it also improves the combustion quality. The authors acknowledge that this study is only a starting basis: further investigation is required to cover all the aspects related to the industrial application of this syngas-Diesel combustion concept, in particular the impact on pollutant emission and on engine durability.


2017 - Improvement of thermal comfort and energy efficiency in historical and monumental buildings by means of localized heating based on non-invasive electric radiant panels [Articolo su rivista]
Lodi, Chiara; Magli, Susanna; Contini, FRANCESCO MARIA; Muscio, Alberto; Tartarini, Paolo
abstract

Energy efficiency and thermal comfort in historic buildings are very often hampered by preservation needs. This issue is particularly relevant for historical and monumental buildings, which currently represent a large part of the historic buildings stock in Europe. For such protected buildings most of the available retrofitting solutions are not feasible and alternatives have to be investigated to guarantee their usability potential. The purpose of this study is therefore to present a methodology to evaluate the potential of electric radiant panels as retrofitting solutions for historical and monumental buildings, focusing on thermal comfort and energy saving potential when compared with conventional fossil-fuel-based heating systems. In fact, the non-invasiveness and flexibility of electrical panels make them one of the few feasible solutions for protected buildings. An original methodology is developed to evaluate the performance of such localized heating systems; the methodology is based on a dynamic simulation model, calibrated with temperature measurements, which takes into account the geometry and technical characteristics of electrical radiant panels and allows different control strategies to be compared. The methodology is applied to a relevant Italian historical building. The results show that the panels, despite their well-known low-exergy efficiency, may become a viable and attractive solution for historical buildings without undermining their preservation requirements. Apart from significantly increasing thermal comfort, electric radiant panels may also allow annual heating energy savings up to 70% for the selected building.


2017 - Multi-phase fluid dynamic of syngas flow across a throttle body in a gasifier-engine system [Relazione in Atti di Convegno]
Allesina, Giulio; Pedrazzi, Simone; Puglia, Marco; Morselli, Nicolò; Mason, Jim; Tartarini, Paolo
abstract

Electronically controlled throttle valves are often used in syngas fueled engines in order to maintain the engine speed constant under variable load and gas composition conditions. The producer gas carries two macrocategories of pollutants: tars (naphthalene, benzene, toluene etc. in vapor phase) and particulate matter; a high concentration of these species leads, almost certainly, to governor stuck or failure. These malfunctions force to engine shutdown. Since it is not always possible to move towards to a better syngas filtration, especially on small scale systems, it is fundamental to investigate the way of fouling of this device. This preliminary study lead to the conclusion that a combined CFD and psychrometric approach is required for a better comprehension of the fouling phenomena.


2017 - Preliminary Analyses on an Algae-Based Water Scrubber for Syngas Cleaning [Articolo su rivista]
Allesina, G; Pedrazzi, S; Altunoz, M; Morselli, N; Puglia, M; Allegretti, F; Leonardi, C; Giorgini, L; Arru, L; Tartarini, P
abstract

Common issues of the gasification systems relate to filtering apparatus. Dry filtering processes are simple and reliable. However, the filtering material defines the maximum and minimum temperature at which the filter can operate properly. In addition, dry filtration is not effective on light tar compounds (i.e. benzene and toluene) or ammonia compounds. On the other hand, despite being very efficient, wet filters drop the gas temperature below the line of condensation of tar, ammonia and steam. The resulting condensate is normally disposed at a high cost on account of the high amount of hydrocarbons it contains. This work investigates the effects of a specific micro-algae growth on the waste-water from a syngas water scrubber. The results demonstrated the capability of the algal growth in the tar-contaminated water in which a certain amount of contaminants have been dissolved. Quantitative analyses of the compounds outlined the effect of algal growth on the reduction of several chemical species derived from the syngas filtration.


2017 - Spent coffee grounds as heat source for coffee roasting plants: Experimental validation and case study [Articolo su rivista]
Allesina, Giulio; Pedrazzi, Simone; Allegretti, Francesco; Tartarini, Paolo
abstract

The aim of this work is to validate a new sustainable economic circle where coffee roasting companies recycle spent coffee grounds as a source of thermal energy to produce roasted coffee. The green coffee beans need a significant quantity of heat in the roasting process and this energy could be obtained from the spent coffee grounds discarded by espresso bars. According to the concept of circular economy, a coffee company collects the coffee disposed by the bars where it was brewed, and uses it in a heat generator for the roasting process. This paper presents the feasibility of SCG-wood sawdust pelletization and combustion in a 29 kWthair furnace. Results of the tests report a thermal efficiency of 41.2% instead of 37.7% obtained with only wood pellet. In addition, the case study of a small Italian roasting company is discussed. The company produces about 5 tons of roasted coffee per day and it uses 400 Nm3/day of natural gas as heat source. The company totally satisfies its energy demand through wood-coffee pellet combustion instead of natural gas. According to the business plan, the pay-back period of the investment is four years after which company CO2emissions significantly decrease.


2017 - The energetic recover of biomass from river maintenance: The rebaf project [Relazione in Atti di Convegno]
Pedrazzi, Simone; Allesina, Giulio; Morselli, Nicolò; Puglia, Marco; Barbieri, Luisa; Lancellotti, Isabella; Ceotto, Enrico; Cappelli, Giovanni Alessandro; Ginaldi, Fabrizio; Giorgini, Loris; Malcevschi, Alessio; Pederzini, Chiara; Tartarini, Paolo
abstract

This paper exposes the first year of activities regarding an Italian regional project called REBAF (RecuperoEnergeticoBiomasse Alvei Fluviali = Energetic Recover of River Biomasses). The project concerns the modeling, realization and experimental validation of innovative pathways for the exploitation of grass and woodsy biomasses from river maintenance operations. The project is focused on the Secchia river situated in the mid North of Italy. The final goal is to make the river maintenance operations self-sustainability from the economic and environmental point of views. During the first year of the project, the typical biomasses of the Secchia river was recognized and quantified. Poplar was chosen as major representative of the wood biomasses. An evaluation about wood biomass quantity obtainable for every hectare of riverbanks maintenance was made. Several gasification tests of poplar wood chips from river maintenance was done in a small CHP gasifier. The biochar obtained was characterized and it was applied on field to some giant reed plantations in order to evaluate if there will be a productivity increase with biochar as soil amendant. In addition, a model to evaluate the giant reed annual productivity in the Secchia river banks was developed.


2017 - The use of on-line colorimetry for tar content evaluation in gasification systems [Articolo su rivista]
Quinlan, Brendan; Kaufmann, Bear; Allesina, Giulio; Pedrazzi, Simone; Hasty, Julia; Puglia, Marco; Morselli, Nicolò; Tartarini, Paolo
abstract

Gasification of biomass has the potential to become a relevant technology for a sustainable future. However, the content of tar in the gas produced through gasification needs to be managed properly in order to increase the reliability of the technology. Accurate measurement of tar gas concentrations enables management and technology improvement. Standardized offline measurement methods require a long time to produce a numerical result from a test. This work presents a novel colorimetric method to assess the tar concentration contained in syngas. The method uses an apparatus that includes a heated thimble filter (to remove particulate), gas quenching with isopropyl alcohol (IPA), a vapor knockout and cooling system including a final stage fritted glass bubbler/impinger, IPA removal via a peristaltic pump controlled by a capacitive level sensor, IPA flow metering, colorimeter for IPA/tar solution light absorbance measurement, and gas pumping/metering circuit. The method is robust and fast because it is based on a continuous light absorbance measurement. The system was compared against the tar protocol standard showing good correlation between average absorbance and tar concentration. Results demonstrate the capability of the proposed method to give continuous real-time measurement of the tar concentration in the gas.


2017 - University energy planning for reducing energy consumption and GHG emissions: The case study of a university campus in Italy [Articolo su rivista]
Lodi, Chiara; Malaguti, Vania; Contini, Francesco Maria; Sala, Luigi; Muscio, Alberto; Tartarini, Paolo
abstract

Reduction of energy consumption in educational buildings, and primarily in University buildings, is nowadays a relevant issue. The evaluation of the energy performance of these buildings is complex due to the variability in their construction age and their intermittent and wide variety of uses. In addition, these buildings are often characterized by a scarce availability of energy end use data, which makes challenging to benchmark energy performance and to inform energy policy decisions. To tackle this problem, this paper explores the use of simple indicators linking low-frequency available energy consumption data to variables measuring building characteristics and weather conditions. The use of such indicators is accompanied by detailed ad-hoc energy audits, including activities in the area of building management systems and dynamic energy simulation. The case study chosen is the Italian University of Modena and Reggio Emilia, which recently developed a Sustainability Plan targeting reductions in GHG emissions to 2020 and identified a framework for investment over the next 5 years to meet University targets. The results of the study shows that simple performance indicators can provide a first insight into the buildings energy performance and identify critical buildings that require detailed analysis. The results of the energy audits support the decision of actions to reduce heating and cooling energy consumption while maintaining acceptable thermal comfort for occupants.


2017 - Vine prunings biomass as fuel in wood stoves for thermal power production [Articolo su rivista]
Puglia, Marco; Pedrazzi, Simone; Allesina, Giulio; Morselli, Nicolò; Tartarini, Paolo
abstract

Wine industries by-products consist in various biomasses. The major in abundance are the vine prunings, derived from the annual vine plant maintenance. Literature suggests a variable production of 1-5 ton/year for every hectare of vine plantation. Vine prunings have a higher heating value of about 18 MJ/kg and an ash amount of about 4%. This paper analyzes the behavior as solid fuel in domestic stove of 4 variety of vine prunings from Emilia Romagna, a region in the north of Italy. First, physical and chemical characterization of the biomass samples were performed, then ash sintering and melting temperatures were evaluated. Combustion tests on a commercial multi-fuel biomass stove were performed. During the tests, mean combustion temperatures, biomass consumption, thermal power and combustion efficiency were calculated and compared with data regarding tests with A1 plus wood pellets. In addition, qualitative results about biomass sintering and stove flame stability was discussed. Results show a thermal efficiency comparable to the one obtained with wood pellet and the sintering of ashes was neglectable. Concluding, pre-treated vine prunings confirmed good properties as fuel in wood stove.


2017 - Water-mist systems for fire-protection of saunas [Relazione in Atti di Convegno]
Santangelo, Paolo Emilio; Tarozzi, Luca; Bettati, Massimiliano; Tartarini, Paolo
abstract

Saunas have become increasingly popular in the built environment (e.g., recreation centers, resorts). However, their structural components – timber benches – and the presence of fabric and chemicals represent an inherent fire hazard. High environmental temperatures, short circuits of electrical heaters and direct contact with incandescent materials may cause fires and even explosions, if the former are not effectively controlled and suppressed. Passive fire-protection systems are commonly combined with fixed, discharge-based ones; among these latter, water mist is a promising technology, especially if no sprinkler installation is already present. An enclosed, real-scale facility was built and instrumented to evaluate control and suppression performance of a water-mist-based system against fires occurring in a sauna-like configuration. Typical timber benches (~ 43 kg) were used; a wood-crib fire accelerated by a heptane-pool fire was also employed to reproduce an electrical-heater failure. Two water-mist nozzles were installed at the ceiling height (2.4 m), each of which had a 12.96 m2 area coverage. The discharge was operated at 100 bar. Various design and configuration parameters were varied: ignition-source location, presence of drywall boards and distance between benches and walls, distance between nozzles and walls, (natural) ventilation, initial room temperature (20 – 80 °C). Heat detectors were inserted to govern discharge activation upon a fixed threshold (180 s); the test chamber was equipped with K-type thermocouples and hot-plate thermometer to measure the heat-flux trend. The system proved able to successfully control and contain the fire, as the bench damage ratio was kept below 5% throughout the whole experimental campaign. However, 2 instances of suppression without extinction occurred, one of which related to the supposed most challenging configuration (ventilated compartment, initial temperature > 80 °C and bigger nozzle-to-wall distance). Ignition-source location, wood-crib damage ratio and air-gap between benches and walls did not appear to impact on suppression performance.


2016 - Dynamic analysis of the heat released by tertiary buildings and the effects of urban heat island mitigation strategies [Articolo su rivista]
Magli, Susanna; Lodi, Chiara; Contini, Francesco Maria; Muscio, Alberto; Tartarini, Paolo
abstract

This study presents a comprehensive approach for calculating buildings' energy contribution to the formation of urban heat island (UHI). For this purpose, the heat released by building envelope and HVAC system has been taken into account, while longwave radiation to the sky has been excluded from the calculation, as it is not so relevant to the UHI effect. Several strategies to minimize the UHI phenomenon and their effects on the heat released have been considered along the whole-year period. An existing educational building has been selected as case study. The selected building is considered representative for a wide range of tertiary buildings with an intermittent operation mode. Results have been obtained by dynamic simulation models, which have been validated with measured indoor air temperature data. Despite a moderate reduction of the energy contribution to the UHI effect during winter, which is commonly considered unfavorable, the effectiveness of cool coating application in reducing the heat released during summer has been clearly demonstrated. On the other hand, it was found that a higher level of envelope insulation is not yielding a significant reduction of the heat released, especially during summer.


2016 - Effects of upgrading systems on energy conversion efficiency of a gasifier - fuel cell - gas turbine power plant [Articolo su rivista]
Pedrazzi, Simone; Allesina, Giulio; Tartarini, Paolo
abstract

This work focuses on a DG-SOFC-MGT (downdraft gasifier - solid oxide fuel cell - micro gas turbine) power plant for electrical energy production and investigates two possible performance-upgrading systems: polyphenylene oxide (PPO) membrane and zeolite filters. The first is used to produce oxygen-enriched air used in the reactor, while the latter separates the CO2 content from the syngas. In order to prevent power plant shutdowns during the gasifier reactor scheduled maintenance, the system is equipped with a gas storage tank. The generation unit consists of a SOFC-MGT system characterized by higher electrical efficiency when compared to conventional power production technology (IC engines, ORC and EFGT). Poplar wood chips with 10% of total moisture are used as feedstock. Four different combinations with and without PPO and zeolite filtrations are simulated and discussed. One-year energy and power simulation were used as basis for comparison between all the cases analyzed. The modeling of the gasification reactions gives results consistent with literature about oxygen-enriched processes. Results showed that the highest electrical efficiency obtained is 32.81%. This value is reached by the power plant equipped only with PPO membrane filtration. Contrary to the PPO filtering, zeolite filtration does not increase the SOFC-MGT unit performance while it affects the energy balance with high auxiliary electrical consumption. This solution can be considered valuable only for future work coupling a CO2 sequestration system to the power plant.


2016 - Full-scale experiments of fire control and suppression in enclosed car parks: A comparison between sprinkler and water-mist systems [Articolo su rivista]
Santangelo, Paolo Emilio; Tarozzi, Luca; Tartarini, Paolo
abstract

Recent efforts to investigate car-park fires and understand the related mechanisms have fostered the need for analyses of suppression performance against this type of fire scenario. This work aims at providing an insight into the ability of sprinklers and water-mist systems to control and extinguish a fire within an enclosed car park through a series of real-scale experiments. Three cars were employed in each test: the central one was ignited by a heptane pool fire and the adjacent ones served as targets. Two configurations were explored: in the first one, a nozzle was placed directly at the vertical axis of the ignition source, whereas the ignition source was located between the area coverage of four nozzles in the second one. The sprinkler system mainly served as a reference; two values of discharge density were evaluated for water mist at high operative pressure and a biodegradable surfactant was also tested against the most challenging configuration. A quantitative analysis of free-burn and discharge phases by temperature measurements was coupled with radiant heat-flux measurements and an assessment of post-fire damage. Sprinkler and water-mist systems were capable of containing the fire spread and thermally controlling the fire, thus preventing structural damage. The water mist’s ability to overpower the plume and reach the burning surfaces proved more effective than that of sprinklers, especially as no nozzles were located right above the ignition surface. The higher discharge density showed better capability of preventing re-ignition phenomena and suppression was attained in both the investigated configurations, which suggests that a certain amount of flux is also needed to achieve flame cooling. The additive had promising impact on suppression performance; however, more tests are required to specifically explore its ability to enhance thermal control.


2016 - Modified diesel engine fueled by syngas: Modeling and experimental validation [Relazione in Atti di Convegno]
Pedrazzi, Simone; Allesina, Giulio; Morselli, Nicolò; Puglia, Marco; Rinaldini, Carlo Alberto; Savioli, Tommaso; Mattarelli, Enrico; Giorgini, Loris; Tartarini, Paolo
abstract

Diesel engines are robust and reliable machine for stationary electrical energy production. In fact, these engines are designed to run continuously for thousands of hours and with low maintenance. However, several issues affect the application of syngas as fuel in this kind of engines. The full conversion from diesel to gas fuel need the presence of the spark plug instead of the diesel injection. Therefore, the high compression ratio in this kind of engines increase the possibility of the knocking phenomenon inside the combustion chamber. The knocking damages the engine mechanical structure and reduce the engine reliability. Several works set the limit of the compression ratio to 17 in order to overcome this issue. In addition, the velocity of the syngas combustion flame is higher compared to the diesel one as result to the presence of hydrogen in the syngas. This difference forces to reduce the spark ignition time from 0 to 15 ° in advance respect the Bottom Top Dead Center (BTDC) in order to limit the peak pressure inside the cylinders to the design value of the engine. Aim of this work is to compare results of a 0D mathematical model of a converted diesel engine with the results obtained in an experimental campaign. For the tests a Fiat Power Train (FPT) 4.5 liters commercial diesel engine converted to syngas is used. The model calculates the maximum power output of the engine at different rpm starting from syngas composition, airsyngas mixture temperature and diesel nominal power. The model takes into account the friction losses, air to fuel ratio and intake manifold pressure. Experimental tests were run on a gasification facility consisting in a fixed bed wood chip downdraft gasifier that generates syngas to fuel the FPT engine. The engine is connected to a MeccAlte generator for electrical power production. An Arduino based controller sets the position of the air valve in order to stabilize the lambda value of the exhaust of the engine to 1.05. A variable electrical load was applied and it was increased as long as the engine was able to drag the generator at 1500 rpm. During the tests, the following parameters were monitored: syngas volumetric flow rate and composition, syngas pollutants concentration (tar, particulate and water), air-gas mixture temperature and intake manifold pressure. An HT electrical circuit analyzer recorded the power output of the generator. Several tests were run at 1500 rpm varying the air-syngas mixture temperature and the intake manifold pressure and experimental results was compared to 0D model predictions. A good agreement of the model to experimental data was achieved. Syngas conversion reduces the maximum electrical power output of the engine generator from 49.7 kW to about 22 kW as result of the lower air-syngas mixture calorific value and density compared to diesel-air mixture. However, the engine mechanical efficiency is comparable using syngas or diesel fuel (about 30%) and pollutant emissions are strongly lower with syngas fuel.


2016 - Preliminary analyses on an algae-based water scrubber for syngas cleaning [Abstract in Atti di Convegno]
Allesina, Giulio; Pedrazzi, Simone; ALTUNOZ HATIPOGLU, Meltem; Morselli, Nicolo'; Puglia, Marco; Leonardi, Chiara; Giorgini, L; Arru, Laura; Tartarini, Paolo
abstract

Aim of this work is to try to put together the two worlds of syngas filtering and syngas upgrading trough the use of a water-algae water photo-bio-scrubber. The system studied consists of a 10 kWel downdraft gasifier provided with a water scrubber where the syngas is bubbled in a solution of water, nutrients, algae and artificial light (. The heat provided by the syngas keeps the scrubber to the proper temperature where tars are condensed and algae can grow at proper rate. At the same time the CO2 content in the gas can be, in part, converted into biomass by the algae. From the scrubber it is disposed a multi-phase liquid composed of water, biomass, tars and char. The first analysis carried out in this work consisted in a two phases process of the gas. First, in the gasification system, part of the gas was derived into a simple water scrubber where all the flows where measured and the temperature was kept constant at 30 °C. Then the water obtained in such a way was used as basis for algae grown in lab conditions. Results shown the capability of such a system to be used in existing gasification facilities.


2016 - Preliminary Analysis on an Algae-Based Water Scrubber For Syngas [Abstract in Atti di Convegno]
Allesina, Giulio; Pedrazzi, Simone; ALTUNOZ HATIPOGLU, Meltem; Morselli, Nicolo'; Puglia, Marco; Allegretti, Francesco; Leonardi, Chiara; Giorgini, Loris; Arru, Laura; Tartarini, Paolo
abstract

In this study, two major advantages of microalga Neochloris oleoabundans have been taken into account: purification of the syngas contaminant water (SCW) and providing biomass yield from microalgae growth by using syngas contaminant together with BG11 microalgal growth medium [1] as a feedstock. 10 kW imbert type downdraft gasifier fueled with wood chips have been used to obtain syngas contaminant [2]. A certain amount of the wood-gas is derived after the biofiltering process and is sent to the Water Algae Photo-Bio-Scrubber System (WAPBS): a series of Drechsel bottles are filled with syngas cleansing water (SCW). Tar and particulate are trapped in the water inside the WAPBS, while part of the syngas contaminant is available for the micro algae to be converted into biomass. At the end of the process char and tar content of the syngas contaminant used by microalgae have been observed and microalgal growth of N. oleoabundans have been monitored during the process of WAPBS.


2016 - Uses of a water-algae-photo-bio-scrubber for syngas upgrading and purification [Relazione in Atti di Convegno]
Allesina, Giulio; Pedrazzi, Simone; Arru, Laura; Altunöz Hatipoğlu, Meltem; Puglia, Marco; Tartarini, Paolo
abstract

Aim of this work is to try to put together the two worlds of syngas filtering and syngas upgrading troughthe use of a water-algae water photo-bio-scrubber. The system studied consists of a 10 kWel downdraft gasifier provided with a water scrubber where the syngas is bubbled in a solution of water, nutrients, algae and artificial light (. The heat provided by the syngas keeps the scrubber to the proper temperature where tars are condensed and algae can grow at proper rate. At the same time the CO2content in the gas can be, in part, converted into biomass by the algae. From the scrubber it is disposed a multi-phase liquid composed of water, biomass, tars and char. The first analysis carried out in this work consisted in a two phases process of the gas. First, in the gasification system, part of the gas was derived into a simple water scrubber where al the flows where measured and the temperature was kept constant at 30 °C. Then the water obtained in such a way was used as basis for algae grown in lab conditions. Results shown the capability of such a system to be used in existing gasification facilities.


2016 - Uses of a Water-Algae-Syngas-Photo-Scrubber for gas upgrading and purification in small-scale gasifiers [Abstract in Atti di Convegno]
Allesina, Giulio; Pedrazzi, Simone; Arru, Laura; ALTUNOZ HATIPOGLU, Meltem; Tartarini, Paolo
abstract

Aim of this work is to try to put together the two worlds of syngas filtering and syngas upgrading trough the use of a water-algae water photo- bio-scrubber. The system studied consists of a 10 kWel downdraft gasifier provided with a water scrubber where the syngas is bubbled in a solution of water, nutrients, algae and artificial light (. The heat provided by the syngas keeps the scrubber to the proper temperature where tars are condensed and algae can grow at proper rate. At the same time the CO2 content in the gas can be, in part, converted into biomass by the algae. From the scrubber it is disposed a multi-phase liquid composed of water, biomass, tars and char. The first analysis carried out in this work consisted in a two phases process of the gas. First, in the gasification system, part of the gas was derived into a simple water scrubber where all the flows where measured and the temperature was kept constant at 30 °C. Then the water obtained in such a way was used as basis for algae grown in lab conditions. Results shown the capability of such a system to be used in existing gasification facilities.


2015 - Approaching sustainable development through energy management, the case of Fongo Tongo, Cameroon [Articolo su rivista]
Allesina, Giulio; Pedrazzi, Simone; Sgarbi, Federico; Pompeo, Elisa; Roberti, Camilla; Cristiano, Vincenzo; Tartarini, Paolo
abstract

This work is aimed at defining a possible solution for sustainable energy development in the Menoua Department, West Cameroon. The purpose of the cooperation between ALA Milano Onlus and the Biomass Energy Efficiency Laboratory of the University of Modena and Reggio Emilia was to analyze the case study in order to propose a solution for energy production capable of meeting the needs of the Cameroonian society while also heading towards a sustainable development. Primary researches suggested that the most viable solution was to integrate the corn food processing with the gasification of the cobs. The thermo-conversion process was modeled with a black-box approach; the results of the model were further compared with the energy required for corn processing, therefore demonstrating the sustainability and virtuosity of the chosen solution. A commercial 20 kW$$_el$$el gasifier was selected for supplying electrical power to three central buildings: the city hall, the Chaufferie and the school. This solution is a security measure assuring continue power supply to these vital buildings. Furthermore, it will bind the relation between the rural and the city areas through the energy exchange process.


2015 - Digestate as bio-fuel in domestic furnaces [Articolo su rivista]
Pedrazzi, Simone; Allesina, Giulio; Belló, Tobia; Rinaldini, Carlo Alberto; Tartarini, Paolo
abstract

This study investigates the use of the biogas power plants byproduct (digestate) as biofuel in an ordinary domestic air furnace. The digestate, disposed by a 1 MW biogas plant located in Italy, was dried out and pelletized in order to be used as fuel in a wood pellet furnace with 29 kW(th) of nominal power, commonly installed in industrial HVAC systems. The first test was carried out starting from a heavily dried pellet called "digestate 0" characterized chemically and physically in order to obtain its composition, while its ashes were tested using an optical thermal dilatometer for the softening point evaluation. This first test outlined that the "digestate 0" pellets were not suitable for combustion applications even when mixed with an equal part of pure wood pellets. The research then focused on the raw digestate drying process through a set of physical and chemical tests. It was found that a temperature of 150 degrees C maximizes the higher heating value of the new "digestate 1" at 16.6 MJ/kg. However, to further avoid the ash sintering, "ultimate digestate" pellets were prepared mixing 50% of "digestate 1" and 50% of wood. The digestate obtained in such a way was experimentally tested through several runs of the air furnace. In these tests, the overall efficiency as well as the furnace emissions was measured.


2015 - Experimental and numerical analysis of thermal interaction between two droplets in spray cooling of heated surfaces [Relazione in Atti di Convegno]
Santangelo, Paolo Emilio; Corticelli, Mauro Alessandro; Tartarini, Paolo
abstract

Dropwise cooling is a subject of interest for numerous industrial applications, which fosters fundamental research on the related mechanisms. The present work is focused on studying the cooling effect of two water droplets gently released onto a heated solid surface. The nominal initial temperature of the substrate was lower than 100 °C, thereby referring to evaporation regime. An experimental and numerical approach was employed to analyze heat-transfer phenomena both at the solid/liquid interface and over non-wetted regions, thus evaluating mutual interaction between droplets. Infrared thermography was used as the experimental technique: a facility was built to measure surface temperature from below through a fully non-intrusive approach. An infrared-transparent disk served as the solid substrate; its black-painted upper surface allowed heating and droplet deposition to occur on a blackbody. A numerical code was developed to model heat-transfer mechanisms within all bodies and at all interfaces, employing the finite-volume discretization method. Numerical results showed very good agreement with experimental temperature profiles and heat-flux distribution was predicted over the whole sampling region. Cooling effect was quantitatively determined, together with the extent of the mutual-interaction region, where the influence of a multi-droplet configuration was proved higher and longer with respect to a single-droplet one.


2015 - Experimental-analytical evaluation of sustainable syngasbiodiesel CHP systems based on oleaginous crop rotation [Relazione in Atti di Convegno]
Allesina, Giulio; Pedrazzi, Simone; Rinaldini, Carlo Alberto; Savioli, Tommaso; Morselli, Nicolo'; Mattarelli, Enrico; Tartarini, Paolo
abstract

This work is aimed at investigating how the solutions adopted for the SRF (short rotational forestry) can be applied to oleaginous cultures for bioenergy production with a dual fuel diesel engine. The method is based on four sub-systems: a seed press for oil production, a downdraft gasifier, a biodiesel conversion plant and a dual fuel biodiesel IC engine for CHP (combined heat and power) production. The plant is analytically modeled except for the IC engine that was tested via experimental analysis. Results showed that, in the hypothesis of 8000 hours/year of power plant run, a surface of 27 hectares can supply enough syngas and biodiesel to run a CHP unit with nominal electrical power of 13.61 kW. Moreover, the experimental analysis outlined how the engine running with dual fuel is not almost affected by significant losses in its performance. Besides, the use of syngas yields strong benefits in terms of soot emissions (measured by an opacimeter), as well as in terms of brake fuel conversion efficiency.


2015 - Increased maize power production through an integrated biogas-gasification-SOFC power system [Relazione in Atti di Convegno]
Pedrazzi, Simone; Allesina, Giulio; Puglia, Marco; Guidetti, Luca; Tartarini, Paolo
abstract

This work is aimed at demonstrating by modeling and simulation how a synergy of state-of-the-art technologies can boost of about 50% the maximum power output that can be obtained from maize silage biogas power plants. The starting point is the subdivision of the maize plant into grains and stover (that is composed of cobs, stalks and leaves). Grains are rich of starch, soluble sugars, fat and protein suitable for the anaerobic digestion, instead the stover is rich of hemicellulose and lignin which are characterized by a slow and incomplete degradability. This consideration brings to the core of the paper: grains are used as fuel in an anaerobic digester, while stover is converted into syngas in a fixed bed downdraft gasifier reactor. The biological degradation of grains is based on equilibrium kinetic models obtained from literature review, the stover gasification is modeled with an equilibrium model implemented in Python™ language. Biogas and syngas streams are used together as fuel in a Solid Oxide Fuel Cell (SOFC) conversion unit modeled through a MatlabTM script. Simulations were done considering a conventional maize silage biogas power plant with 100 kW electrical nominal power. Results outlined that the SOFC has a higher conversion rate than the conventional IC engine, in fact the replacement of the generator with a SOFC increases the power output of the plant to about 118 kW. Finally, the combined effects of coupling digestion of grains with the gasification of the stover and the use of a SOFC boost the peaks power output to 150 kW.


2015 - Modeling of coupling gasification and anaerobic digestion processes for maize bioenergy conversion [Articolo su rivista]
Allesina, Giulio; Pedrazzi, Simone; Guidetti, Luca; Tartarini, Paolo
abstract

This work estimates the advantages of using maize as fuel in a power plant composed of an anaerobic digester, a gasifier and an Internal Combustion (IC) engine. The digester is fed with maize grains, while, the remaining part of the plant, the stover, is gasified. Then biogas and syngas streams are both used as fuel into the engine. The performance of this plant was evaluated coupling gasification and anaerobic digestion mathematical models. Results of the proposed solution are compared with the performance of a 100 kW biogas power plant fed with the whole crop silaged. Results show that the overall energy yield of the improved solution is 39% higher than the conventional one fed with maize silage. This method will lead to the design of small and cheap digesters as a result of the increased conversion rate. In fact, the solution proposed fully converts the high cellulose-fiber parts of the maize plant that were tough to degrade in anaerobic digesters.


2015 - Which thermochemical conversion process for agricultural waste? Physical and chemical analyses to guide the choice [Articolo su rivista]
Pedrazzi, Simone; Allesina, Giulio; Puglia, Marco; Morselli, Nicolò; Tartarini, Paolo
abstract

This study investigates how physical and chemical analyses may lead the choice of the more suitable thermochemical energy conversion process for agricultural wastes. Four different case study are presented: corn cobs, digestate pellets from anaerobic digestion, wood biomass from river maintenance and seed cake from vegetable oil production. For all the cases analyzed the physical as well as the chemical characterization of the feedstocks are presented and discussed. Outputs of these analyses are: chemical composition, moisture content, ash content, ash softening point and particle size. These outputs, together with logistic considerations about availability and preconditioning of the biomasses allow to properly define the optimal process for each biomass. Three thermochemical processes are taken into account: pyrolysis, gasification and direct combustion.


2014 - Biodiesel and electrical power production through vegetable oil extraction and byproducts gasification: Modeling of the system [Articolo su rivista]
Allesina, Giulio; Pedrazzi, Simone; Tebianian, Sina; Tartarini, Paolo
abstract

Aim of this work is to introduce an alternative to the standard biodiesel production chain, presenting an innovative in situ system. It is based on the chemical conversion of vegetable oil from oleaginous crops in synergy with the gasification of the protein cake disposed by the seed press. The syngas from the gasifier is here used to produce electrical power while part of it is converted into methanol. The methanol is finally used to transform the vegetable oil into biodiesel. Through a coupled use of ASPEN PLUS (TM) and MATLAB (TM) codes, a rapeseed, soy and sunflower rotation, with a duration of three year, was simulated considering 15 ha of soil. This surface resulted sufficient to feed a 7 kW(el) power plant. Simulation outputs proven the system to be self-sustainable. In addition, economical NPV of the investment is presented. Finally the environmental, economical and social advantages related to this approach are discussed.


2014 - Energy and economical comparison of possible cultures for a total-integrated on-field biodiesel production [Relazione in Atti di Convegno]
Allesina, Giulio; Pedrazzi, Simone; S., Tebianian; Muscio, Alberto; Tartarini, Paolo
abstract

This work is aimed at investigating the energy conversion effectiveness and the economical advantages of a total integrated solution for on-field biodiesel and electrical energy production. The system proposed here is based on the synergy of four sub-systems: a seed press for oil production, a downdraft gasifier, a biodiesel conversion plant and a Solid Oxide Fuel Cell (SOFC). Two possible culture rotations, suggested by literature review, were analyzed here from economical and energy balance points of view. Both the rotations were composed of oleaginous crops only, therefore the seeds collected from the different cultures were pressed, then the protein cake produced in the process was gasified in the downdraft reactor. The gasification process was modeled here, and its output suggested that, for a precise number of hectares, the syngas obtained through the cake gasification was enough for producing methanol required for oil-biodiesel conversion and feeding a 10-kW SOFC. The purge line in the methanol reactor was used in the SOFC as well. The system was simulated using ASPEN PLUSTMand MATLABTMcodes. Results of the SOFC and gasifier models underlined the capability of the fuel cell to work with this particular system, furthermore the whole system analysis suggested that the surface required for sustainability of the processes is a function of the rotation choice. In both cases little surfaces ranging from 11 to 21 hectares were found to be enough for system self-sustainability with a ROI under 7 years in all the operating conditions analyzed.


2014 - Energy-Based Assessment of Optimal Operating Parameters for Coupled Biochar and Syngas Production in Stratified Downdraft Gasifiers [Relazione in Atti di Convegno]
Allesina, Giulio; Pedrazzi, Simone; LA CAVA, Emma; Orlandi, Michele; Hanuskova, Miriam; Fontanesi, Claudio; Tartarini, Paolo
abstract

Biochar represents a valuable solution for carbon sequestration. Infact, it has aroused the interest of the scientific community due to its resistance to the degradation and its potential of soil improving. Stratified downdraft gasifier reactors are characterized by extreme design simplicity and it was proved that are able to operate with non-homogeneous feedstock. On the other hand, stratified reactors dispose a higher amount of char when compared to other downdraft gasifier. This work is aimed at characterizing the char produced through downdraft stratified reactors. Particular conditions which maximize both the quality and the amount of syngas and biochar was investigated. The whole system was evaluated through a composed coefficient Ip (performance index) which takes into account the energy content in the gas stream and the characteristics of the char produced. A lab-scale reactor, able to operate under different conditions, was designed considering the requirements of this work. It was implemented with a sophisticated heating system which allow us to control the reactor surface temperatures independently zone to zone. Results shown the capability of stratified gasifiers to be used for biochar disposal. Results outlined the Ip trend as function of the SV of the gasifier. and tar production was considered to find the more suitable condition.


2014 - Mismatch losses in PV power plants [Articolo su rivista]
Lorente, Daniel Gómez; Pedrazzi, Simone; Zini, Gabriele; Dalla Rosa, Alberto; Tartarini, Paolo
abstract

In this paper, two different PV arrays have been simulated in order to quantify the electrical mismatch loss in each one of them. The simulations have been performed both in the standard condition (STC) and in the dynamic conditions which implement the meteorological data from the two different locations. Two methods have been applied to calculate the mismatch losses. The first one (the simplified method) assumes that all modules are at the tolerance limit and the second one (the I-V curve method) calculates the loss instead from the I-V characteristic of the modules or of the module series/parallel. Also an ordering procedure starting from the I-mp value of the module has been evaluated. The results show a very small mismatch loss in the small PV plant of 40 modules, furthermore the ordering does not influence so much the loss in this case. Instead, the loss in the larger array of 320 modules is bigger and the ordering method presents a more significant influence.


2014 - Porous filtering media comparison through wet and dry sampling of fixed bed gasification products [Relazione in Atti di Convegno]
Allesina, Giulio; Pedrazzi, Simone; Montermini, Luca; Giorgini, L.; Bortolani, G.; Tartarini, Paolo
abstract

The syngas produced by fixed bed gasifiers contains high quantities of particulate and tars. This issue, together with its high temperature, avoids its direct exploitation without a proper cleaning and cooling process. In fact, when the syngas produced by gasification is used in an Internal Combustion engine (IC), the higher the content of tars and particulate, the higher the risk to damage the engine is. If these compounds are not properly removed, the engine may fail to run. A way to avoid engine fails is to intensify the maintenance schedule, but these stops will reduce the system profitability. From a clean syngas does not only follow higher performance of the generator, but also less pollutants in the atmosphere. When is not possible to work on the gasification reactions, the filter plays the most important role in the engine safeguard process. This work is aimed at developing and comparing different porous filters for biomass gasifiers power plants. A drum filter was developed and tested filling it with different filtering media available on the market. As a starting point, the filter was implemented in a Power Pallet 10 kW gasifier produced by the California-based company «ALL Power Labs». The original filter was replaced with different porous biomasses, such as woodchips and corn cobs. Finally, a synthetic zeolites medium was tested and compared with the biological media previously used. The Tar Sampling Protocol (TSP) and a modified «dry» method using the Silica Gel material were applied to evaluate the tars, particulate and water amount in the syngas after the filtration process. Advantages and disadvantages of every filtering media chosen were reported and discussed.


2014 - Spray cooling by gently-deposited droplets: Experiments and modeling of heat-transfer mechanisms [Relazione in Atti di Convegno]
Santangelo, Paolo Emilio; Corticelli, Mauro Alessandro; Tartarini, Paolo
abstract

Numerous engineering applications involve dropwise cooling of hot solid surfaces, which has become a major research task for both academia and industry. This work focuses on single-phase evaporation regime, proposing a fully non-intrusive technique to measure the solid/liquid interface temperature and a simple numerical code to evaluate heat flux. A comparison between a single droplet and two sequentially released droplets is presented. Infrared thermography was used to measure the transient contact temperature of droplets released onto a BaF2 disk coated by a black-painted layer; interface temperature was measured from below through the solid body. The total released volume of water was kept constant; droplet Weber number was lower than 70; the initial surface temperature was nominally 80 °C. A self-developed numerical code was developed to simulate the evaporation mechanism under single-phase evaporation regime. The three-dimensional energy diffusion equation describing the transient within both the liquid and the solid phase was discretized by the finite-volume method. The model aims at ultimately predicting the heat-flux distribution at the solid/liquid interface. Flux distribution was obtained for both the single- and the two-droplet case; moreover, heat flux was evaluated all over the sampling region. Validation was performed as a comparison between numerical and experimental temperature datasets at the substrate surface, showing very good agreement for both the cases, especially for the wetted regions. The single-droplet configuration is shown to provide overall higher cooling effect, whereas the multi-droplet has longer and more effective cooling on the area of mutual interaction between droplets.


2013 - Biodiesel production through sinergy of on-field PVO extraction and protein cake gasification [Relazione in Atti di Convegno]
Allesina, Giulio; Muscio, Alberto; S., Tebianian; Pedrazzi, Simone; Tartarini, Paolo
abstract

This work is aimed at demonstrating the advantages of on-field oil extraction and protein cake exploitation from biomasses produced by a three-years crop rotation. The rotation that has been taken into account is rapeseed-sunflowerflax, suitable for most Mediterranean climatic zones. The process is divided in differents phases: extraction of pure vegetable oil (PVO) from seeds, gasification of the protein cake remaining from oil extraction and trans-esterification of the PVO using the methanol obtained by conversion of part of the syngas from gasification. In this way, instead of selling the seeds to the market, it is possible to sell the biodiesel and the electrical energy obtained from an IC engine operating with the excess of syngas. The effectiveness evaluation of this approach has been obtained through energetic and economical modeling of the whole system. The system has been simulated using ASPEN PLUSTM and MATLABTM codes. The results show the advantages related to the installation of micro power plants of 10 kWel, involving little surfaces tilled. The minimum surface necessary for system self-sustainability has been estimated as a function of field productivity and fuels characteristics. Moreover, the outputs of the economical analysis show the effectiveness of this innovative approach.


2013 - Modeling and investigation of the channeling phenomenon in downdraft stratified gasifiers. [Articolo su rivista]
Allesina, Giulio; Pedrazzi, Simone; Tartarini, Paolo
abstract

Downdraft stratified gasifiers seem to be the reactors which are most influenced by loading conditions. Moreover, the larger the reactor is, the higher the possibility to stumble across a channeling phenomenon. This high sensitivity is due to the limited thickness and superficial placement of the flaming pyrolysis layer coupled with the necessity to keep all the zones parallel for a correct running of this kind of gasifier. This study was aimed at modeling and investigating the channeling phenomenon generated by loading condition variations on a 250-kWe nominal power gasification power plant. The experimental campaign showed great variations in most of the plant outputs. These phenomena were modeled on two modified mathematical models obtained from literature. The results of the models confirmed the capability of this approach to predict the channeling phenomena and its dependency on the loading method.


2013 - Modeling and simulation of a DG-SOFC-MGT hybrid system [Relazione in Atti di Convegno]
Pedrazzi, Simone; Allesina, Giulio; Muscio, Alberto; Tartarini, Paolo
abstract

This paper describes the modeling and the simulation of an advanced gasification power plant composed of a Downdraft Gasifier (DG) and a Solid Oxide Fuel Cells - Micro Gas Turbine unit (SOFC-MGT). The gasifier converts the woodsy biomass into syngas that it is cooled and filtered before entering in a compressed storage tanks sub-system. A hybrid SOFC-MGT unit uses the stored syngas to produce electrical energy that it is sent to the electrical grid. The system has been modeled starting from literature. The simulations were made for different types of woodsy biomass over a year long period. Poplar, peach tree and vineyards pruning have been adopted with a variable moisture content ranging from 5% to 30%. The electrical energy produced and the overall electrical efficiency have been calculated setting the biomass consumption to 187 kg/hour for different biomasses and moistures scenarios. Maintenance of the gasifier has taken into account imposing a cycle of 120 hours of operating and 12 hours of maintenance. Starting from that, the storage sub-system has been design to assure the continuous operation of the SOFC-MGT unit all over the annual simulation. Sensitive analysis of the performance of the system varying the biomass type and the biomass moisture have been developed in order to find the best working conditions. Moreover, the annual energy balance of the system has been evaluated with these conditions to point out where the most relevant energy losses take place. Results show that the maximum overall electrical efficiency is around 33.5% for poplar biomass with 10% of moisture. In this scenario the average electrical power production is about 223 kW, the annual electrical energy amount sent to the grid is about 1956 MWh. In this conditions, the 42% of the chemical energy of the biomass is lost in the SOFC-MGT unit.


2013 - Simulation of GEMASOLAR-based solar tower plants for the Chinese energy market: Influence of plant downsizing and location change. [Articolo su rivista]
Amadei, C. A.; Allesina, Giulio; Tartarini, Paolo; Yuting, W.
abstract

In many countries that are experiencing a steep increase of energy demand, there is a growing challenge of responding to this demand by investing in renewable technologies for new power plants. Solar energy seems to be one of the best solutions to reduce the fossil fuels consumption for energy production purposes. In terms of high-power solar plants, concentrating towers are characterized by high efficiencies, but the investment costs are high as well. For this reason, a fundamental issue consists in simulating the solar tower behavior in different locations, in order to provide a precise estimation of both annual energy production and return of the investment. Among these types of solar plants, GEMASOLAR has been recently (2011) put in operation in Andalusia, Spain, and the data that have been obtained by this plant allow one to study its potential for application in different locations. The present work is aimed at simulating the GEMASOLAR plant behavior in some Chinese areas suitable for such a technology. All the simulations proposed here have been obtained through a Solar Advisor Model (SAM). Some of the simulations of the original plant have been modified forcing the plant to run without fossil fuel hybridization or changing its nominal power. After model validation, results have shown encouraging perspectives for the exploitation of this technology in China, with annual overall efficiencies of 14% for the 20 MW power plant (GEMASOLAR nominal power). In addition, the down-scaled plants have been optimized through native SAM software algorithm focusing on geometrical parameters. This procedure has been proved to be able of maintaining a high efficiency (14.97%) even for a 10 MW power plant. The focus has been on pilot plants, since they could represent the first step towards a deep exploitation of concentrating solar thermal power in China, with a relatively low capital risk.


2012 - Aige conference: A kinetic model for a stratified downdraft gasifier [Relazione in Atti di Convegno]
PEDRAZZI, Simone; ALLESINA, GIULIO; TARTARINI, Paolo
abstract

A model for a stratified downdraft gasifier has been developed. It has been adapted from two different models from literature with appropriate modifications and improvements. The new “interacting” model is able to predict the syngas composition, input and output flow rates and the gasifier cold efficiency under different working condition and with different biomass input. It works assuming a constant biomass consumption. The results of the model has been compared to experimental data taken from a downdraft gasifier power plant system with nominal power output of 200 kWel. The plant has been set at 160 kWel in order to avoid system instabilities related to high power runs.


2012 - Full-scale experiments of fire suppression in high-hazard storages: A temperature-based analysis of water-mist systems. [Articolo su rivista]
Santangelo, Paolo Emilio; Tartarini, Paolo
abstract

Water-mist systems have become quite popular over the last two decades as an innovative technology in fire protection. Moreover, insertion of additives to the flow may be applied to provide additionalimprovements in terms of suppression effectiveness and temperature control. The present work consists of an experimental approach within a real-scale facility, which has been aimed at challenging water mistagainst severe fire scenarios. Among them, a high-rise storage has been here explored, being it commonly recognized as strongly hazardous even by technical standards in terms of both nominal fireload and designed physical domain. The system configuration presents high-pressure nozzles at the ceiling; the sole-water flow is compared to water endowed with a commercial additive.The thermal transient within the test chamber has been evaluated during the fire development as the main quantitative parameter; moreover, the fire evolution has been visualized through a post-fireestimation of the damages. Despite the large amount of released smoke and smoldering materials, water mist is shown to be efficient in fire control, if endowed with the chosen additive. On the otherhand, the sole-water flow does not appear suitable for such hazardous conditions under the designed nozzle arrangement.


2012 - Investigation of an equivalence criterion between periodic thermal transmittance of opaque building elements and cool roof or cool color coatings [Relazione in Atti di Convegno]
Lodi, Chiara; Ferrari, Fabio; Muscio, Alberto; Tartarini, Paolo
abstract

At this time, just a few requirements have been introduced in Italy about the summer performance of buildings, one among them concerning the maximum allowed value for the periodical thermal transmittance of opaque building elements. In fact, it is generally assumed that thermal cycles induced by solar radiation at the external surfaces can be substantially damped through the thickness of roofs and walls thanks to properly low values of their periodic thermal transmittance. The result is generally achieved by giving roofs and walls an adequate levels of either thermal insulation or thermal inertia, but this is generally reflected in the adoption of a high surface mass and makes it difficult to use wooden roofs, plasterboard structures or sandwich panels with foam insulation. However, using an outer coating with high solar reflectance, identified with the terms of cool roof or cool color in the technical nomenclature used in the U.S.A., permits to dampen the thermal cycles induced by solar radiation directly at the outer surface rather than through the thickness. In the present paper, we investigate an equivalence criterion between periodic thermal transmittance and solar reflectance by means of dynamic calculation approaches. The criterion is studied in terms of containment of either thermal energy needs for air conditioning or discomfort of the built environment.


2012 - Modelling and simulation of a wind-hydrogen CHP system with metal hydride storage [Articolo su rivista]
Pedrazzi, Simone; G., Zini; Tartarini, Paolo
abstract

This paper describes the modelling and simulation of a wind-hydrogen system aimed at supplying electrical and thermal residential loads, where the thermal load is in part supplied by a catalytic hydrogen combustion device with hydrogen stored in a metal hydride system composed of a cluster of five metal hydride tanks equipped with a metal foam heat exchanger.The complete mathematical model has been developed from models available in literature and describing the different sub-systems that constitute the overall wind-hydrogen system. It has been laterimplemented in a multi-domain software environment to simulate system operations.Results over a year-long simulation show complete stand-alone capabilities, with an electrical efficiency and a combined heat and power efficiency of 8.2% and 12.5% respectively. At the end of thesimulation period, a hydrogen annual surplus of 110.5 kg is left over which can, for instance, be used to feed a hydrogen powered car for about 9500 km.


2012 - Solar hydrogen energy systems: Science and technology for the hydrogen economy [Monografia/Trattato scientifico]
G., Zini; Tartarini, Paolo
abstract

From "Preface":The work is structured into eleven chapters to present the reader with advanced knowledge on the functioning and implementation of a solar hydrogen energy system, which combines different technologies efficiently and harmoniously to convert renewable energies into chemical energy (stored under the form of hydrogen) andthen to a much more exploitable form of energy, electricity.


2011 - Assessment and improvement of the performance of antisolar surfaces and coatings [Articolo su rivista]
Libbra, Antonio; Muscio, Alberto; Siligardi, Cristina; Tartarini, Paolo
abstract

Solar reflectance and thermal emittance are key parameters to evaluate solar heat gains through opaquebuilding elements. A high solar reflectance allows building surfaces to minimize absorption of solarenergy, whereas a high thermal emittance allows returning to the environment most of the solar energythat is however absorbed by any actual surface. Therefore, summer overheating of buildings can beprevented by selecting external coatings with proper values of both properties.In this work, the role of radiative properties is explained in quantitative terms. Standard test methodsfor their measurement are also presented. The behavior of some typical cool roof surfaces is then analyzed,in order to point out the limits of qualitative selection criteria and demonstrate the need of quantitativeapproaches to enable product comparison and development. Eventually, the perspectives offered by theuse of advanced materials and coatings are also highlighted.


2011 - Dropwise cooling in single-phase evaporation: Infrared experiments on single- and multi-droplet configurations [Relazione in Atti di Convegno]
Santangelo, Paolo Emilio; Tartarini, Paolo
abstract

A large variety of applications in engineering and physics is based on evaporative cooling of solid surfaces: this phenomenon is commonly generated through a spray of water droplets. A quite relevant background is currently available in the field, with specific regard to impingement and heat-transfer mechanisms. However, the thermal transient at the solid-liquid interface still requires some deeper understanding, together with the thermal interac-tion among a certain number of droplets and the solid substrate. The present study work has been aimed at ex-perimentally investigating these physical aspects under single-phase evaporation regime, which is ultimately re-lated to temperatures of the solid surface lower than 100 °C at atmospheric pressure. Moreover, the droplets have been gently deposited (Weber number lower than 30), thus allowing to neglect impact phenomena affect-ing their initial shape. Single- and multi-droplet configurations (two droplets) have been considered to carry out a quantitative investigation of thermal interaction among subsequently released droplets and then refer and com-pare this case to the classic cooling effect induced by a single droplet. Infrared thermography has been here em-ployed to evaluate evaporation and thermal recovery transients at the solid-liquid interface: an experimental apparatus has been built and a suitable methodology has been developed to perform fully non-intrusive meas-urements. Thermal trends are finally expressed as functions of both time and space, thus thoroughly represent-ing the thermal behavior of the considered configurations.


2011 - Elementi di fisica tecnica per l'ingegneria [Traduzione di Libro]
Corticelli, Mauro Alessandro; Barozzi, Giovanni Sebastiano; Muscio, Alberto; Stalio, Enrico; Tartarini, Paolo
abstract

Scopo del testo è introdurre ai principi della termodinamica, della meccanica dei fluidi e della trasmissione del calore attraverso un approccio integrato, assai importante per lo studente ingegnere


2011 - Experimental parametric analysis of water-mist sprays: An investigation on coalescence and initial dispersion [Relazione in Atti di Convegno]
Santangelo, Paolo Emilio; Tartarini, Paolo; Valdiserri, Paolo
abstract

An experimental approach and parametric analysis are here presented to investigate some dynamic aspects of water-mist sprays operating at high supply pressure. An already proposed methodology (P.E. Santangelo, 2010, Exp. Therm. Fluid Sci., 34, pp. 1353-1366) has been extended to a three-dimensional analysis, that emphasizes the characteristic drop-size evolution along the axial coordinate of the spray. Therefore, an evaluation of coalescence and secondary-atomization phenomena along the spray axis results as the ultimate scope of this study. With regard to dispersion, the initial-velocity field has been experimentally determined both as a contour/vector map and as magnitude profiles at different distances from the injector outlet. In addition, some evaluation of the spray-cone angle has been proposed, resulting from a simple geometric approach to the already mentioned maps. Advanced laser-based diagnostics has been employed to perform experimental measurements: a Malvern Spraytec device has been used to measure drop-size distribution and Particle Image Velocimetry has been chosen to evaluate both velocity and cone angle. Moreover, a mechanical patternator has been employed to introduce flux measurements as an averaging quantity. Two nozzles having different orifice diameter have been employed and operative pressure has been set at a value of interest for fire-protection applications. Copyright © 2011 by ASME.


2011 - Full scale experiments on water-mist fire-suppression systems in High-Hazard Storages (HHS) – A temperature-based comparison between sole water and water/additive flow [Articolo su rivista]
Santangelo, Paolo Emilio; Tartarini, Paolo
abstract

Water-mist systems have gained wide popularity over the last twenty years as an innovative technology in fire protection. Moreover, insertion of additives in the flow is typically applied to provide additional improvements in terms of suppression effectiveness and temperature control. The present work consists of an experimental approach in a real-scale facility, which has been aimed at challenging water mist against severe fire scenarios. The sole water flow is compared to water endowed with a commercial additive, the F-500 by Hazard Control Technologies Inc. As the fire setting, a high-rise storage has been explored: this real scenario is commonly recognized as severely hazardous even by technical standards, because of both its nominal fire load and the designed physical domain. The thermal transient within the test chamber during the fire development has been measured as the main quantitative parameter: K-type thermocouples have been employed to the purpose over a set of remarkable locations. Moreover, the fire evolution has been evaluated through a post-fire estimation of the damages. Despite the large amount of released smoke and smoldering materials, water mist is shown to be efficient in fire control, if endowed with the chosen additive, while the sole water flow does not appear suitable for such hazardous conditions.


2011 - Full-scale experiments on water-mist fire-suppression systems in High-Hazard Storages (HHS): A temperature-based comparison between sole water and water/additive flow [Relazione in Atti di Convegno]
Santangelo, Paolo Emilio; Tartarini, Paolo
abstract

Water-mist systems have gained wide popularity over the last twenty years as an innovative technology in fire protection. Moreover, insertion of additives in the flow is typically applied to provide additional improvements in terms of suppression effectiveness and temperature control. The present work consists of an experimental approach in a real-scale facility, which has been aimed at challenging water mist against severe fire scenarios. The sole water flow is compared to water endowed with a commercial additive, the F-500 by Hazard Control Technologies Inc. As the fire setting, a high-rise storage has been explored: this real scenario is commonly recognized as severely hazardous even by technical standards, because of both its nominal fire load and the designed physical domain. The thermal transient within the test chamber during the fire development has been evaluated as the main quantitative parameter: K-type thermocouples have been employed to the purpose over a set of remarkable locations. Moreover, the fire evolution has been visualized through a post-fire estimation of the damages. Despite the large amount of released smoke and smoldering materials, water mist is shown to be efficient in fire control, if endowed with the chosen additive, while the sole water flow does not appear suitable for such hazardous conditions.


2011 - Infrared experiments of dropwise cooling: Single- and multi-droplet configurations in single-phase evaporation [Relazione in Atti di Convegno]
Santangelo, Paolo Emilio; Tartarini, Paolo
abstract

A wide number of engineering applications is based on evaporative cooling, which is usually performed through a spray of water droplets: the scientific background in the field is considerable, notably about heat-transfer mechanisms. This work has been focused on investigating dropwise cooling of hot solid surfaces under single-phase evaporation regime (i.e.: temperature of the solid substrate lower than 100 °C at atmospheric pressure). The droplet Weber number has been kept lower than 30 (gently deposited), thus yielding to negligible impact phenomena on the initial shape of the droplets. Both single- and multi-droplet configurations (two droplets) are here considered to quantitatively investigate the thermal interaction among droplets subsequently released and compare this latter case to the cooling effect induced by a single droplet. The thermal transient during evaporation and subsequent recovery process has been here experimentally evaluated by infrared thermography: an experimental apparatus has been built and a suitable methodology has been developed to measure the solid-liquid interface temperature. The thermal trends are then expressed as functions of both time and space, thus allowing to determine the thermal behavior of the considered configurations.


2011 - La questione delle maggiorazioni ex UNI 10351 sulla conducibilità termica dei materiali per l’edilizia: risultati di una campagna di verifica mediante apparato hot-box [Relazione in Atti di Convegno]
Francesco, Tardini; Massimiliano, Magagnoli; Giancarlo, Ferrero; Libbra, Antonio; Muscio, Alberto; Tartarini, Paolo
abstract

La limitazione dei fabbisogni energetici degli edifici è un obiettivo prioritario per tutta l’Unione europea, in cui sono comprese aree territoriali fortemente antropizzate. Azioni incentivanti ed imposizioni normative sono perciò in continua evoluzione, in relazione sia agli edifici di nuova costruzione che al patrimonio edilizio esistente. Anche in Italia, gli interventi di risanamento energetico degli edifici esistenti, a livello di involucro e di impianti, sono attualmente supportati da specifici incentivi fiscali. Tra i vari tipi di intervento che si possono adottare passa spesso in secondo piano l’adozione di sistemi di ventilazione meccanica controllata, che pure offre interessantissime opportunità, tanto dal punto di vista della riduzione dei fabbisogni energetici quanto da quello del miglioramento del confort e della qualità dell’aria negli ambienti abitati. In questo lavoro si intende tracciare il quadro della normativa inerente la ventilazione degli ambienti e gli impianti di ventilazione meccanica controllata, con particolare riferimento alla riqualificazione degli edifici residenziali. Si svilupperà, quindi, un’analisi critica delle tecnologie utilizzabili, con l’intento di formulare proposte di intervento contraddistinte da semplicità di realizzazione e di calcolo.


2011 - Use of soft computing techniques in renewable energy hydrogen hybrid systems [Capitolo/Saggio]
Zini, Gabriele; Pedrazzi, Simone; Tartarini, Paolo
abstract

Soft computing techniques are important tools that significantly improve the performance of energy systems. This chapter reviews their many contributions to renewable energy hydrogen hybrid systems, namely those systems that consist of different technologies (photovoltaic and wind, electrolyzers, fuel cells, hydrogen storage, piping, thermal and electrical/electronic control systems) capable as a whole of converting solar energy, storing it as chemical energy (in the form of hydrogen) and turning it back into electrical and thermal energy. Fuzzy logic decision-making methodologies can be applied to select amongst renewable energy alternative or to vary a dump load for regulating wind turbine speed or find the maximum power point available from arrays of photovoltaic modules. Dynamic fuzzy logic controllers can furthermore be utilized to coordinate the flow of hydrogen to fuel cells or employed for frequency control in micro- grid power systems. Neural networks are implemented to model, design and control renewable energy systems and to estimate climatic data such as solar irradiance and wind speeds. They have been demonstrated to predict with good accuracy system power usage and status at any point of time. Neural controls can also help in the minimization of energy production costs by optimal scheduling of power units. Genetic or evolutionary algorithms are able to provide approximate solutions to several complex tasks with high number of variables and non-linearities, like optimal operational strategy of a grid-parallel fuel cell power plant, optimization of control strategies for stand-alone renewable systems and sizing of photovoltaic systems. Particle swarm optimization techniques are applied to find optimal sizing of system components in an effort to minimize costs or coping with system failures to improve service quality. These techniques can also be implemented together to exploit their potential synergies while, at the same time, coping with their possible limitations. This chapter covers soft computing methods applied to renewable energy hybrid hydrogen systems by providing a description of their single or mixed implementation and relevance, together with a discussion of advantages and/or disadvantages in their applications. © Springer-Verlag Berlin Heidelberg 2011.


2010 - A solar hydrogen hybrid system with activated carbon storage [Articolo su rivista]
Zini, G.; Marazzi, R.; Pedrazzi, S.; Tartarini, Paolo
abstract

A solar hydrogen hybrid system has been developed to convert, store and use energy from renewable energy sources. The theoretical model has been implemented in a dynamic model-based software environment and applied to real data. A photovoltaic sub-system drives a residential load and, if a surplus of energy is available, an electrolyzer to produce hydrogen which is stored in a cluster of nitrogen-cooled tanks filled with activated carbons; when needed, hydrogen is used in a fuel cell to supply power to the load. Hydrogen storage is achieved through physisorption at low temperature and low pressures. Physisorptionstorage provides safer operations along with good gravimetric and volumetric capacities at costs comparable to or smaller than compression or liquefaction storage.Results show that the system has stand-alone capabilities with a surplus production of hydrogen at end of year. Tanks are reasonable in size and weight for stationary applications,and surplus can contribute to recharge batteries or fill tanks for non-stationary uses.


2010 - Actual solar reflectance of roof surfaces andstandard energy performance of Italian buildings in summer [Relazione in Atti di Convegno]
Libbra, Antonio; Muscio, Alberto; Tartarini, Paolo
abstract

Solar reflectance or its complement to unity, solar absorptance, are key parameters to evaluate solar gains through opaque elements and predict summer performance of buildings. For their evaluation, Italian technical rule UNI/TS 11300-1 prescribes a standard approach based on colors, distinguishing between dark-, intermediate- and light-colored surfaces and assigning to each category a fixed value of solar absorptance or reflectance. This approach, however, may be simplistic. In fact, an experimental campaign performed at the Energy Efficiency Laboratory of the University of Modena and Reggio Emilia showed that typical materials for Italian building such as roof tiles, coated tiles, paints or sealing membranes can show similar colors, but very different values of solar properties.In this paper, the calculation method currently in force in Italy for solar gains is briefly presented and then applied to a general analysis. In particular, the range of variability for summer performance of buildings is discussed in relation to the color-based evaluation approach, also taking into account measurement results obtained for some roofing solutions typical of Italy.


2010 - Alcune considerazioni sulla conversione in energia primaria dei fabbisogni da fonti rinnovabili ed assimilate [Relazione in Atti di Convegno]
A., Lambruschi; G., Bizzarri; Muscio, Alberto; Tartarini, Paolo
abstract

La determinazione dei fabbisogni energetici convenzionali degli edifici e l’attribuzione agli stessi di una classe di prestazione energetica discendono dal calcolo del fabbisogno di energia soddisfatto dalle diverse fonti energetiche utilizzate, attualmente da valutare in termini di energia primaria attraverso coefficienti di conversione specifici per ogni fonte.A livello nazionale sono già stati prescritti specifici fattori di conversione per i combustibili fossili e per l’energia elettrica, ma non per fonti rinnovabili o assimilate quali le biomasse combustibili o per il calore ottenuto da processi cogenerativi o reflui termici.In questo lavoro si tenta di tracciare il quadro della normativa nazionale inerente la valutazione dell’energia primaria ottenuta da fonti rinnovabili, nonché di quella consumata dai sistemi cogenerativi, considerando anche alcuni orientamenti a livello internazionale e regionale e sviluppando una analisi critica ispirata dai dettati fondamentali della Direttiva 2002/91/CE, con l’intento di formulare alcune semplici proposte di valutazione convenzionale, supportate da specifiche argomentazioni di natura tecnico-scientifica e normativa.


2010 - Analisi delle dinamiche di transizione di fase in materiali per accumulo termico incapsulati [Relazione in Atti di Convegno]
Libbra, Antonio; Muscio, Alberto; Tartarini, Paolo
abstract

I materiali a transizione di fase per accumulo termico consentono di realizzare accumulatori con volumi, masse e superfici disperdenti molto contenuti, ma vanno opportunamente incapsulati per potersi interfacciare con il fluido termovettore degli impianti termoidraulici. Si pone perciò il problema dell'ottimizzazione delle geometrie e dei materiali delle capsule di contenimento, onde assicurare un efficiente scambio termico e, quindi, adeguate velocità di accumulo e rilascio del calore.In questo lavoro vengono esaminate e perfezionate alcune soluzioni analitiche utili a prevedere le dinamiche di avanzamento del fronte di transizione di fase in un PCM. Inoltre, viene presentato un modello numerico originale, atto a simulare con elevato livello di realismo i transitori termici dei PCM incapsulati. Il modello è stato validato tramite le soluzioni analitiche ed è stato infine sperimentato per indagare alcune problematiche fondamentali circa l’utilizzo dei PCM incapsulati.


2010 - Analisi di involucri edilizi con elevata inerzia termica integranti materiali a transizione di fase (PCM) [Articolo su rivista]
Libbra, Antonio; Muscio, Alberto; Tartarini, Paolo
abstract

Un adeguato confort termoigrometrico estivo e la limitazione dei fabbisogni energetici per condizionamento possono essere conseguiti conferendo agli elementi dell’involucro edilizio un’inerzia termica sufficiente a smorzare le fluttuazioni di temperatura dovute al ciclo solare. Al tal fine, destano particolare interesse i materiali in grado di accumulare elevate quantità di energia termica sotto forma di calore latente di transizione di fase, i cosiddetti PCM (phase change material), la cui integrazione nell’involucro edilizio può consentire significativi benefici a parità di masse e spessori di parete, oppure considerevoli riduzioni delle masse e degli spessori stessi. In questo lavoro si riportano i risultati di alcune analisi sulla realizzazione e sulle problematiche di progettazione di elementi dell’involucro edilizio con massa superficiale contenuta ma elevata inerzia termica in virtù dell’integrazione di PCM.


2010 - Approaches for the assessment and improvement of performance of antisolar surfaces [Relazione in Atti di Convegno]
Libbra, Antonio; Muscio, Alberto; Tartarini, Paolo
abstract

Solar reflectance and thermal emittance are key parameters to evaluate the solar heat gains through opaque building elements. A high solar reflectance allows building surfaces to minimize absorption of solar energy, whereas a high thermal emittance allows returning to the environment most of the solar energy that is however absorbed by any actual surface. Therefore, summer overheating of buildings can be prevented by selecting external coatings with proper values of both properties. In this work, the role of radiative properties is explained in quantitative terms and standard test methods for their measurement are briefly presented. The behavior of some typical cool roof surfaces is then analyzed, in order to point out the limits of qualitative selection criteria and demonstrate the need of quantitative approaches to enable product comparison and development. Eventually, the perspectives offered by the use of advanced materials and coatings are also highlighted.


2010 - Complete modeling and software implementation of a virtual solar hydrogen hybrid system [Articolo su rivista]
Pedrazzi, S.; Zini, G.; Tartarini, Paolo
abstract

A complete mathematical model and software implementation of a solar hydrogen hybrid system has been developed and applied to real data. The mathematical model has been derived from sub-models taken from literature with appropriate modifications and improvements. The model has been implemented as a stand-alone virtual energy system in a model-based, multi-domain software environment.A test run has then been performed on typical residential user data-sets over a year-long period. Results show that the virtual hybrid system can bring about complete grid independence; in particular, hydrogen production balance is positive (+1.25 kg) after a year’s operation with a system efficiency of 7%.


2010 - Direct Numerical Simulation of Forced Convection over Steps at Low Prandtl Number [Relazione in Atti di Convegno]
Angeli, Diego; Barozzi, Giovanni Sebastiano; Errico, Orsola; Stalio, Enrico; Tartarini, Paolo
abstract

Convective heat transfer in transitional and weakly turbulent conditions is investigated numerically for a Prandtl number Pr =0.025, representative of liquid lead-bismuth eutectic (LBE). The geometry selected is a periodic channel with cavities. Finitevolumesimulations are carried out on structured orthogonal curvilinear grids, for two different values of the Reynolds numberin the weakly turbulent range. The main features of the mean and instantaneous flow fields are described. The influence of flowseparation mechanisms and turbulent mixing on local and global heat transfer rates is also discussed, considering the effect ofdifferent thermal boundary conditions imposed at the channel walls.


2010 - Evaporative cooling of heated solid surfaces: Two-droplet thermal interaction [Relazione in Atti di Convegno]
Santangelo, Paolo Emilio; Corticelli, Mauro Alessandro; Tartarini, Paolo
abstract

Evaporative cooling represents a key subject for both academia and industry: the behavior of sessile droplets has been studied in detail over many decades and a large body of literature is currently available on heat-transfer mechanisms. The present work is focused on the thermal transient occurring as one or two water droplets are gently released (We < 30) onto a heated solid surface; moreover, the single-phase-evaporation regime is here considered. Infrared thermography has been employed to perform experimental measurements of the temperature trend at the solid-liquid interface: a suitable facility has been built to carry out measurements from below, thus introducing a fully non-intrusive approach. As the numerical task of this study, a computational code has been developed to predict the entire evaporation mechanism together with the thermal transient of the solid substrate: the three-dimensional energy-diffusion equation has been discretized through the finite-volume method and the simulations have been based on a structured non-uniform mesh. The proposed modeling has been made capable of reproducing both the single- and the multi-droplet configuration. A remarkably good agreement is shown between experimental and numerical outcomes in terms of temperature, thus resulting in a realistic simulation of droplet interaction over both the spatial domain and the time coordinate (evaporation and recovery).


2010 - Experimental and numerical analysis of droplet cooling [Relazione in Atti di Convegno]
Tartarini, Paolo; Corticelli, Mauro Alessandro; Santangelo, Paolo Emilio
abstract

Dropwise cooling represents a major subject of interest for both academic and industrial researches. The present work is focused on investigating the thermal transient occurring as two water droplets are gently released (We < 30) onto a heated solid surface. This latter has been kept at initial temperature lower than 373.15 K to analyze the single-phase-evaporation regime. To the purpose, both an experimental and a numerical approach have conveniently been employed.Infrared thermography has been used to evaluate the temperature trend at the solid-liquid interface: an experimental facility has been built to carry out measurements from below, thus realizing a fully non-intrusive approach. A transparent-crystal disk has been inserted to serve as the solid substrate; its upper surface has been painted by a black coating, thus providing a black-body surface as the solid-liquid interface. The infrared thermocamera has been placed below and perpendicular to that surface; temperature has been thereby measured, being emissivity a known parameter.A numerical code has been developed to predict the involved physical phenomena: temperature trend, evaporation time and evaporated flux result from discretizing the three-dimensional energy-diffusion equation by the finite-volume method. Moreover, the model is based on structured non-uniform mesh to adapt to the occurring temperature gradients. Very good agreement is shown between experimental and numerical outcomes in terms of thermal transient and recovery.


2010 - Fire control and suppression by water-mist systems [Articolo su rivista]
Santangelo, Paolo Emilio; Tartarini, Paolo
abstract

The present work is an attempt to offer a comprehensive review of literature contributions, phenomenology and relevant results on water-mist systems. In particular, the water mist characterization and behavior in the field of fire control and suppression have been identified as the main areas of investigation. Some key parameters have been analyzed to gain a quantitative evaluation of the physical phenomena related to water-mist systems. The water-mist fire suppression systems are an excellent alternative to halon fire protection systems, and they are now being used in many areas, including marine and industrial applications. Therefore, a wide survey of the complete number of literature works on this topic would exceed the full length of the present paper and only some examples of important contributions will be mentioned here. This paper proposes an introductory list of relevant literature works and this reference survey is then deepened with work and result details on suppression mechanisms, spray characterizations and experimental and numerical approaches. The final summary stresses out that a lot of experimental and numerical research and much application experience are still needed to gain better knowledge on water-mist systems, even if they already seem to be very promising in terms of efficiency and potentialities in fire control and suppression.


2010 - Fire suppression by water-mist sprays: Experimental and numerical analysis [Relazione in Atti di Convegno]
Santangelo, Paolo Emilio; Tartarini, Paolo; Pulvirenti, Beatrice; Valdiserri, Paolo; Marshall, André W.
abstract

Water-mist systems have become a promising technology in the fire-fighting field over the last twenty years. The present work is aimed at employing the available knowledge on watermist sprays in an experimental and numerical analysis of the suppression mechanism. Therefore, a water-mist system has been operated within a typical fire case. Most notably, this latter is constituted by a heptane pool fire: experiments have been carried out inside a test chamber, where a set of thermocouples has conveniently been placed to evaluate the thermal transient at different locations of interest. Some free-combustion tests have been run as a benchmark to validate combustion models. Then, a typical water-mist nozzle has been inserted and activated to realize control, suppression and potential extinction of the generated fire. The recognized FDS (Fire Dynamics Simulator) and Fluent® codes have been challenged in reproducing the test case: thermal transient and suppression time have been considered as parameters for validation. Therefore, the watermist spray has been modeled and the already mentioned results about its characterization have been implemented as initial or boundary conditions. Moreover, the fire scenario has been modeled as well. A good agreement between experimental and numerical results has been obtained, even under some approximations, with specific reference to combustion mechanisms. © 2010 by ASME.


2010 - Realizzazione e validazione preliminare di un apparato hot-box per la misura delle proprietà di trasmissione termica di elementi di parete in opera [Relazione in Atti di Convegno]
F., Tardini; M., Magagnoli; G., Ferrero; Libbra, Antonio; Muscio, Alberto; Tartarini, Paolo
abstract

La normativa nazionale vigente nell’ambito della progettazione e della certificazione energetica degli edifici prevede la valutazione accurata della trasmittanza termica delle pareti opache e, in determinate condizioni, il rispetto di valori limite prestabiliti. Una corretta valutazione della trasmittanza termica risulta altresì fondamentale, a prescindere dalle prescrizioni normative, per prevedere l’effettivo comportamento termico delle singole pareti e dell’involucro edilizio nel suo complesso. Questo lavoro verte sullo sviluppo di un nuovo apparato di misura di tipo hot-box per la determinazione sperimentale della trasmittanza termica di pareti verticali in scala reale. L’apparato, realizzato da Kerakoll SpA in collaborazione con il Laboratorio per l’Efficienza Energetica (EELab) del Dipartimento di Ingegneria Meccanica e Civile di Modena, è basato su sensori di tipo termoflussimetrico ed è conforme alla norma tecnica UNI EN 1934:2000 [1]. In questa sede se ne fornisce un’ampia presentazione e si riportano alcuni risultati preliminari relativi al suo utilizzo.


2010 - Thermal interaction between two droplets in single-phase evaporation [Relazione in Atti di Convegno]
Santangelo, Paolo Emilio; Corticelli, Mauro Alessandro; Tartarini, Paolo
abstract

Dropwise cooling is a major subject for both academic and industrial researches: the behavior of sessile droplets has been extensively investigated over many decades and a large body of literature is focused on heat-transfer mechanisms. The present work is focused on investigating the thermal transient occurring as two water droplets are gently released (We < 30) onto a heated solid surface: the single-phase-evaporation regime is here considered. Infrared thermography has been employed to experimentally evaluate the temperature trend at the solid-liquid interface: an apparatus has been built to carry out measurements from below, thus realizing a fully non-intrusive approach. As a numerical approach, a computational code has been developed to predict the involved physical phenomena: the three-dimensional energy-diffusion equation has been discretized through the finite-volume method and the simulations have been based on a structured non-uniform mesh.Modeling the transient within both the droplets and the solid substrate stands as the primary scope of this approach. Very goodagreement is shown between experimental and numerical results in terms of temperature trends, providing a thorough representation of droplet interaction over both the spatial domain and the evaporation and recovery time.


2010 - Wind-hydrogen energy stand-alone system with carbon storage: Modeling and simulation [Articolo su rivista]
G., Zini; Tartarini, Paolo
abstract

A wind-hydrogen hybrid system with carbon physisorption storage has been developed and implemented within a dynamic model-based software environment. Numerical simulations have been applied to synthetic and real data to evaluate its operations and performance over a 6-month period. Hydrogen is yielded by electrolysis with energy converted from wind, and load is powered either by direct turbine connection, by battery or a fuelcell. Surplus hydrogen is stored by physisorption in a cluster of nitrogen-cooled tanks filled with activated carbons. Physisorption has been modeled after the Ono-Kondo isotherm from laboratory data available in literature. The operating cycle is composed of four transformations: isobar pre-charging at 0.1MPa, isothermal charging at 77K, isobar pre-discharging at 6 MPa, and isothermal discharging at 153K. From our simulation runs, the system can operate as stand-alonegranting total independence from the grid. The storage system has good gravimetric and volumetric capacity(10.8%and 32.5g/l at 6 MPa). Overall system efficiency is estimated to be around 10%. Hydrogen physisorption on carbon seems a potentially feasible storage technique for hydrogen with tanks that are compact and safe, hence apt for stationary and some non-stationary applications.


2009 - Building structures with high thermal inertia based on phase change materials [Articolo su rivista]
Barozzi, Giovanni Sebastiano; Corticelli, Mauro Alessandro; Libbra, Antonio; Muscio, Alberto; Tartarini, Paolo
abstract

In order to ensure the comfort of people who inhabit a building, the building envelope must have thermal inertia great enough to dampen its temperature fluctuations, in particular those due to the solar cycle. The use of materials that can accumulate large amounts of heat in the form of phase change latent heat, the so-called PCM, represents a very interesting approach to make buildings reactive to cyclical thermal loads and achieve better thermal performance with the same wall thickness, or the same thermal performance with reduced wall thickness.The present work is focused onto the development of roofs with small surface mass and high thermal inertia thanks to the integration of PCM. In particular, the relationship between properties of the PCM and thermal behaviour of the roof structure is investigated by numerical simulation. Moreover, the more convenient position of the PCM layer with respect to the thermal insulation layer is investigated for some typical structures to be protected against summer overheating.


2009 - Design and Simulation of Activated Carbon Tanks for Hydrogen Storage [Relazione in Atti di Convegno]
G., Zini; R., Marazzi; Tartarini, Paolo
abstract

While hydrogen production from renewable energy sources does not have real limiting drawbacks, storage instead poses serious questions on whether an adequate solution will ever be achieved. The Department of Energy (USA) set targets for non-stationary storage systems which prove difficult to meet: gravimetric capacity is targeted at 9% (3 kWh/kg) for year 2015. Such targets are though not binding for stationary applications, but still are considered the goal for H2 storage. Classic storage technology (compression, liquefaction) seems not to be the answer.To find alternative storage solutions, a complete hybrid system with hydrogen storage based on physical adsorption of hydrogen on activated carbons was modeled and simulated.


2009 - Discharge and dispersion in water-mist sprays: Experimental and numerical analysis [Relazione in Atti di Convegno]
Santangelo, Paolo Emilio; Tartarini, Paolo; Pulvirenti, Beatrice; Valdiserri, Paolo
abstract

The present study is aimed at modeling a high-pressure water-mist spray employing two classic numerical codes. To this end, an experimental campaign has been performed both to obtain the input data for the numerical approach and to serve as a validating tool to quantify the predictive capability of the proposed models. In particular, experi-ments have been conducted to determine volume-flux distribution, drop-size distribution, initial velocity and spray-cone angle. Advanced laser-based diagnostics (Malvern Spraytec and Particle Image Velocimetry) has been em-ployed together with simple ad hoc built instruments to measure these parameters over a prescribed range of high operative pressures (50-90 bar). Specific measurement methodologies have been developed to gain a proper exper-imental evaluation of any subject of investigation. Then, a computational simulation of the water-mist spray has been implemented in Fluent and FDS (Fire Dynamics Simulator) codes. Characteristic drop size, velocity and cone angle have been introduced as input parameters, while volume-flux distribution has been employed to compare numerical results to experimental data as a final validating task. A good qualitative agreement has been gained: the spray physics appears to be properly expressed by the proposed models. However, intrinsic limitations characterize both the experimental tools and the computational codes and may explain some still-to-be-solved discrepancies from a quantitative point of view.


2009 - Droplet cooling of heated surfaces: Experimental and numerical analysis [Relazione in Atti di Convegno]
Tartarini, Paolo; Corticelli, Mauro Alessandro; Santangelo, Paolo Emilio
abstract

The present work is focused on measuring the transient contact temperature between a droplet and a hot solid sur-face. Experimental tests have been carried out employing infrared thermography. Droplets of bidistilled and deion-ized water have been gently deposited by a precision syringe onto the upper surface of a heated disk. This latter consists of a Barium Fluoride (BaF2) disk, having high transmittance (about 90%) in the 8-12 m range (typical of long-wave infrared cameras). The interface temperature has been measured from below through the solid material by an infrared thermocamera. As far as the solid can be assumed as infrared-transparent, a black coating layer has been applied to allow radiative heating of the solid surface. The bottom surface temperature of the coating is undis-tinguishable from the solid-liquid interface temperature and has been monitored. Single-phase evaporation regime has been analyzed in detail. A numerical code is then presented, which simulates evaporation process of water droplets on hot solid surfaces. The three-dimensional energy-diffusion equation is discretized by the finite volume method and is employed to model the transient temperature within both the droplet and the solid substrate. In this stage of development, the code simulates the substrate cooling effect due to a droplet in single-phase evaporation regime; however, its applicability to nucleate boiling and film boiling regimes can be considered as reasonably pos-sible. The code is implemented in Matlab®, using a modular and flexible architecture. As a final task, numerical re-sults are validated through a comparison with the experimental data.


2009 - Drop-size and initial-velocity measurements in water-mist sprays [Relazione in Atti di Convegno]
Santangelo, Paolo Emilio; Valdiserri, Paolo; Tartarini, Paolo
abstract

An experimental analysis is here proposed on water-mistsprays operating at high supply pressure. Advancedlaser-based diagnostics has been employed to performmeasurements. In particular, a Malvern Spraytec devicehas been used to measure drop-size distribution at various distances from the injector outlet along the spray axis. Moreover, initial velocity has been determined through a PIV analysis. Some evaluations of the spraycone angle have been proposed as an additional outcome of the analysis. Different nozzles have beenemployed to produce the water-mist spray and operativepressure has been set at values of interest for fireprotectionapplications, which constitute the reference field for the present work.


2009 - Dropwise Cooling: Experimental Tests by Infrared Thermography and Numerical Simulations [Articolo su rivista]
Tartarini, Paolo; Corticelli, Mauro Alessandro; L., Tarozzi
abstract

In this paper, infrared thermography is used to measure the transient contact temperature between impinging droplets and hot solid surfaces. Droplets are released onto the heated solid surface of a barium fluoride (BaF2) disk, which has a high transmittance (about 90%) in the 8–12 um range (typical of longwave infrared cameras). The interface temperature is measured from below, through the solid material, by infrared thermography. Since the solid is IR-transparent, a black coating layer is used to allow radiative heating of the surface and provide a method to measure the liquid–solid interface temperature. A numerical code is then presented, which simulates the evaporation of water droplets on hot solid surfaces. At the present stage of development, single-phase evaporation is addressed. The three-dimensional energy diffusion equation, discretized using the finite volume method, is employed to model the transient within both the droplets and the solid substrate. The numerical results are validated by comparison with the experimental data.


2009 - Fuel Cell Systems and Traditional Technologies. Part II: Experimental Study on Dynamic Behavior of PEMFC in Stationary Power Generation [Articolo su rivista]
Venturelli, Lucia; Santangelo, Paolo Emilio; Tartarini, Paolo
abstract

The present work is focused on electric generation for stationary applications. The dynamic behavior of a PEMFC-based system has been investigated at both constant and variable load conditions from an experimental point of view. An analysis of efficiency as a function of time has been proposed to summarize the dynamic performance; moreover, current intensity and voltage have been considered as main parameters of interest from the electric point of view. In addition, other energetic and thermodynamic parameters have been studied in this work. The experimental campaign has been carried out over four test typologies: constant load; increasing and decreasing load; random load. These tests have been planned to challenge the system with a variety of load-based cycles, in the frame of a thorough simulation of real-load conditions.


2009 - Hybrid Systems for Solar Hydrogen: A Selection of Case-Studies [Articolo su rivista]
G., Zini; Tartarini, Paolo
abstract

Twelve case-studies on systems that generate, store and use hydrogen from photovoltaic energy are hereby presented and discussed. Hydrogen generated from direct sunlight is often called solar hydrogen, and the whole process is characterized by having very low CO2 and pollutants emissions. Such systems, comprising of several sub-systems of different technologies, are called hybrid systems. All case-studies are briefly analyzed and the most prominent conclusions reported. Results show that production of solar hydrogen and its subsequent use in fuel cells is technically viable but costs still need to be reduced for widespread adoption. A comparison is given and need for further work highlighted; in particular, researchers should investigate carbon structures as a potential alternative to pressurization or metal hydrides; a complete analysis of the intangible costs and benefits involved should be performed, together with Discounted Cash Flow and Life Cycle Assessment analysis to understand the true nature of such investments and their sustainability in the near future. Performing such a rigorous and complete economical analysis would, for instance, enable governments to design better incentive schemes and propel such technology in real life usage.


2009 - On the characterization of sprays produced by water-mist injectors [Relazione in Atti di Convegno]
Santangelo, Paolo Emilio; Tartarini, Paolo; Marshall, André W.; Bettati, Massimiliano
abstract

The present work is aimed at providing a thorough characterization of the spray produced by a water-mist injector. An experimental investigation on drop-size and flux distribution, initial velocity and spray-cone angle is proposed. These parameters appear to be the most suitable to provide a quantification of atomization and dispersion phenomena in any generic spray. In addition, some numerical simulations of the sprayed flow have been run employing FDS (Fire Dynamics Simulator): its capability of predicting the fluid-dynamics behavior of the spray has been challenged through a comparison with experimental outcomes. An experimental facility has been built to serve as the set for the entire experimental campaign. A typical water-mist nozzle has been inserted and the activity has been focused on one of the available injectors. Laser-based diagnostics has been employed to measure drop size and initial velocity. Most notably, a Fraunhofer-diffraction-based device (Malvern Spraytec) has been used to investigate the former, while the latter has been evaluated through PIV (Particle Image Velocimetry) technique. FDS code has been employed to carry out some simulations of the behavior of the water-mist spray. The implemented settings and initial conditions resulted from the experimental study, while the computational domain has been set to reproduce the test room. Then, numerical predictions have been validated through a comparison with experimental outcomes. In addition, a classic correlation to predict characteristic drop size has been proposed for the present case and validated.


2009 - Proprietà radiative superficiale esterne e fabbisogno energetico estivo dell’involucro edilizio [Relazione in Atti di Convegno]
Libbra, Antonio; Muscio, Alberto; Tartarini, Paolo
abstract

La recente norma tecnica UNI/TS 11300 ha introdotto una metodologia di calcolo del fabbisogno energetico degli edifici armonizzata con gli standard di calcolo internazionali, ma incentrata sulle specificità del parco edilizio e delle tecniche edificatorie italiane. La norma fornisce una procedura adeguatamente articolata e completa per valutare sia il fabbisogno energetico invernale, sia quello estivo, su cui si focalizza il presente studio, tenendo in considerazione i principali processi di scambio termico che hanno luogo al contorno o entro gli elementi dell'involucro edilizio.In questo lavoro le procedure di calcolo degli apporti solari previste dalla norma UNI/TS 11300 vengono presentate sinteticamente e quindi applicate ad un caso di studio, analizzando in particolare l’impatto che le due principali proprietà radiative delle superfici irradiate, la riflettanza solare e l’emissività termica, possono avere sui guadagni solari attraverso gli elementi opachi dell’involucro edilizio e, quindi, sul fabbisogno termico estivo di un edificio.


2009 - Riflettanza solare ed emissività termica per l'efficienza energetica estiva degli edifici [Articolo su rivista]
Libbra, Antonio; Muscio, Alberto; Tartarini, Paolo
abstract

Il raffrescamento estivo degli ambienti abitati comporta un fabbisogno energetico significativo, in molti casi superiore a quelle per riscaldamento invernale. Il legislatore nazionale si sta perciò accingendo ad introdurre limiti stringenti al consumo di energia anche in relazione alla climatizzazione estiva, focalizzandosi nella fase iniziale sull'involucro edilizio.Il principale carico termico da compensare ai fini del condizionamento estivo è generalmente quello conseguente agli apporti solari, che possono aver luogo sia attraverso gli elementi vetrati dell'involucro, sia attraverso quelli opachi. Nel secondo caso, la limitazione degli apporti può essere ottenuta intervenendo su proprietà delle superfici irradiate quali la riflettanza solare e l'emissività termica.In considerazione della necessità di conoscere e misurare la riflettanza solare e l'emissività termica ai fini dell'ottenimento di involucri edilizi efficienti, il Dipartimento di Ingegneria Meccanica e Civile di Modena ha recentemente strutturato uno specifico laboratorio, dotato di strumentazione rispondente ai migliori standard del settore. Il laboratorio ha già avviato studi scientifici ad ampio spettro sul controllo degli apporti solari ed ha allacciato con numerose aziende, rapporti di collaborazione tecnica finalizzati allo sviluppo di materiali e componenti innovativi per l'edilizia.


2009 - Sistemi energetici ibridi ad idrogeno solare per applicazioni residenziali [Articolo su rivista]
Zini, G.; Pedrazzi, S.; Tartarini, P.
abstract

Un sistema ibrido a idrogeno solare è un insieme di sottosistemi didifferente tecnologia (fotovoltaico, elettrolizzatore, fuel-cell, stoccaggio, tubazioni e componentistica, logica e sistemi di controllo elettronici ed elettrici). Esso è capace di immagazzinare, sotto forma di idrogeno, l’energia proveniente dalla radiazione solare e convertirla in energia elettrica e termica quando richiesto dall’utilizzatore [Rom04, Lod97]. Molti studi recenti hanno tentato di dimostrare come sia possibile costruire, in un prossimo futuro, una economia basata su fonti energetiche rinnovabili, contrapposta all’attuale economia fondataprincipalmente sull’impiego di fonti energetiche fossili. Molte sono le difficoltà da superare per poter realizzare sistemi e infrastrutture, ma risolverle permetterebbe di assicurare una totale indipendenza energetica al paese che le adottasse [Pen06, Abd99, Sch99b]. Sistemi ibridi di questo tipo stanno quindi ricevendo molta attenzione proprio per la loro capacità di catturare e immagazzinare l’energia da fonti rinnovabili,che sono, per natura, altamente irregolari. Immagazzinareenergia in particolare sotto forma di idrogeno consenttirebbe altresì di avere a disposizione un combustibile sostitutivo del petrolio per usi nonstazionari, quali l’alimentazione di mezzi di trasporto o di dispositivi portatili come cellulari o computer portatili. Nel presente lavoro verrà trattata la descrizione matematica di un sistema ibrido a idrogeno solare, e verranno descritti i risultati di performance di un sistema virtuale che ne simula e studia il comportamento operativo. Saranno poi riportati due esempi di realizzazioni pratiche di impianti residenziali, traendo infine alcune conclusioni che permetteranno di avere un quadro più completo su questi sistemi.


2009 - Solar Hydrogen Hybrid System with Carbon Storage [Relazione in Atti di Convegno]
Zini, G.; Marazzi, R.; Pedrazzi, S.; Tartarini, P.
abstract

A complete solar hydrogen hybrid system has been developed to convert, store and use energy from renewable energy sources. The theoretical model has been implemented in a dynamic model-based software environment and applied to real data to simulate its functioning over a one-year period. Results areused to study system design and performance.A photovoltaic sub-system directly drives a residential load and, if a surplus of energy is available, an electrolyzer to produce hydrogen which is stored in a cluster of nitrogen-cooled tanks filled with AX-21 activated carbons. When the power converted from the sun is not sufficient to cover load needs, hydrogen isdesorbed from activated carbon tanks and sent to the fuel-cell sub-system so to obtain electrical energy. A set of sub-systems (bus-bar, buck- and boost-converters, inverter, control circuits), handle the electrical power according to a Programmable Logic Control unit so that the load can be driven with adequate Qualityof Service. Hydrogen storage is achieved through physisorption (weak van der Waals interactions) between carbon atoms and hydrogen molecules occurring at low temperature (77 K) in carbon porous solids at relatively low pressures. Storage modeling has been developed using a Langmuir-Freundlich 1st type isotherm and experimental data available in literature. Physisorption storage provides safer operations along with good gravimetric (10.8% at 6 MPa) and volumetric (32.5 g/l at 6 MPa) storage capacities at costs that can be comparable to, or smaller than, ordinary storage techniques (compression or liquefaction).


2008 - Dropwise cooling: a numerical simulation code and its validation by infrared thermography tests [Relazione in Atti di Convegno]
Corticelli, Mauro Alessandro; Santangelo, Paolo Emilio; Tartarini, Paolo
abstract

In this paper, a numerical code is presented, which simulates the evaporation of water droplets on hot solid surfaces. At the present stage of development, single-phase evaporation is addressed. The three-dimensional energy diffusion equation is employed to model the transient within both the droplets and the solid substrate and is discretized using the finite volume method. Infrared thermography is used to measure the transient contact temperature between impinging droplets and hot solid surfaces in order to validate the code by comparison with experimental data. Droplets are released onto the heated solid surface of a barium fluoride (BaF2) disk, which has high transmittance (about 90%) in the 8-12 um range (typical of longwave infrared cameras). The interface temperature is measured from below, through the solid material. Since the solid is IR-transparent, a black coating layer is used to allow radiative heating of the surface and provide a method to measure the liquid-solid interface temperature. The numerical predictions show very good agreement with the experimental data.


2008 - Experimental analysis of flow regimes and pressure drop reduction in oil–water mixtures [Articolo su rivista]
G., Sotgia; Tartarini, Paolo; Stalio, Enrico
abstract

The physical understanding of two-phase flow characteristics in horizontal pipes is of importance in the petroleum industry since significant savings in pumping power can be derived from the water-lubricated transportation of crude oil.An experimental study of water continuous oil–water flow in horizontal pipes is performed using mineral oil and tap water of viscosity ratio about 900 and density ratio 0.9. A set of seven different pipes of Pyrex and Plexiglas where used, with diameters ranging between 21 and 40 mm. Pressure drop measurements, flow pattern maps and clear pictures of the oil–water flow are reported in this article together with comprehensive comments. The results obtained are compared to empirical laws, theoretical findings and experimental results by different authors in the literature.In order to identify the regions with operational conditions that are suitable for applications, a novel criterion for the location of the annular/stratified transition is proposed which is based only on experimental observations.


2008 - Experimental analysis of stationary power generation by PEMFC [Relazione in Atti di Convegno]
Venturelli, Lucia; Santangelo, Paolo Emilio; Tartarini, Paolo
abstract

The present work has been conducted focusing on electric generation for stationary applications. The general aim is to understand how a PEMFC-based system works along a prescribed time and how it responds to load variations. An experimental setup has been built. Many issues have been of interest for this experimental research. Effectiveness is the core of this study because its trend as a function of time represents the question to be accomplished in order to summarize the real behavior of these systems. Moreover, from the electric point of view, current intensity and voltage basically represent the characteristic parameters, while produced energy, power and fuel consumption are subjects to be investigated from the energetic and thermodynamic side. The experimental campaign has been carried out following four main directions. Long-time tests have been conducted at a constant load; step-by-step tests have been conducted at both increasing and decreasing load and finally tests have been run at completely random load. As far as the minimum and the maximum power given by the device were a priori known, the tests have been conducted in order to simulate a load-based cycle as realistic as possible. Therefore the dynamic behavior of the system has been investigated with a strong focus on stack and net effectiveness.


2008 - Spray characterization of high pressure water mist injectors: Experimental and theoretical analysis [Relazione in Atti di Convegno]
Santangelo, Paolo Emilio; Ren, Ning; Tartarini, Paolo; Marshall, André W.
abstract

This study is focused on characterizing the spray released by a water mist injector at high pressure. To this end, an experimental campaign has been performed employing non intrusive techniques to investigate both drop size and initial velocity over a prescribed range of operative pressure. In particular, a laser-diffraction-based instrument (Malvern Spraytec) has been used to determine the characteristic diameter. An alternative method has been developed to reconstruct the drop-size trend in respect to fluid fraction: drop-size data have been averaged through mass flux distribution. This latter parameter has been measured by a mechanical patternator ad hoc built. Moreover a classic predictive formula for Sauter Mean Diameter has been validated through a physical analysis based on inviscid-fluid assumption. Velocity field has been studied by PIV technique. The proposed measurement methodology has been discussed and both maps and values have been finally stressed out. An experimental evaluation of the spray cone angle has been realized as an additional result of the PIV tests.


2007 - Discharge and dispersion analysis of water mist sprays [Relazione in Atti di Convegno]
Santangelo, Paolo Emilio; Ren, Ning; Tartarini, Paolo; Marshall, André W.
abstract

Water mist is an increasingly popular suppression choice for many industrial and residential applications. At the same time, Computational Fluid Dynamics (CFD) analysis is becoming an accepted method for evaluating fire hazards and fire protection design performance. Water mist system design and development would benefit greatly from CFD based analysis. However, the fire suppression problem is extremely complex concerning many aspects of fluid dynamics, heat transfer, and combustion. For accurate simulations, CFD models describing these physics are required along with establishing appropriate practices for computational problem definition. The current study focuses on atomization and dispersion. Spray measurements, models, and simulations are presented and evaluated for high pressure (above 80 bar) water mist systems. One representative commercially available mist injector (645 J12C B1 by PNR Italia S.r.l.) was selected and drop size measurements were performed in a large quiescent room providing basic discharge characteristics. Furthermore, novel atomization models coupled with the NIST Fire Dynamics Simulator (FDS) were used to predict the initial spray and its subsequent dispersion for a posteriori comparisons with measurements. The primary modeling and measurement challenges related to fire suppression spray dispersion have been identified in this study and are discussed in some detail along with suggested practices for improved simulation of water mist sprays.


2007 - Droplet Cooling: Theory, Experiments and Models. [Relazione in Atti di Convegno]
Tartarini, Paolo
abstract

This work is aimed at presenting a comprehensive review of the cooling effect that liquid droplets induce on hot solid surfaces. In particular, the review addresses theoretical results, experimental studies and modeling approaches, highlighting fundamental results from early studies as well as important contributions from recent research approaches. The characteristics of sessile and impinging droplets are presented, and the governing parameters of both cases of droplet cooling are pointed out. Although a very large number of significant works is shown to be available, this study emphasizes the need to unify the experimental research and the modeling efforts in order to provide better predictive correlations.A final part of this paper focuses on recent experimental results obtained by the non-intrusive method of infrared thermography, which appears to be very promising in terms of useful information for modeling efforts and improvements of cooling efficiency.


2007 - Dropwise Cooling: Experimental Tests by Infrared Thermography and Numerical Simulations [Relazione in Atti di Convegno]
Tartarini, Paolo; Corticelli, Mauro Alessandro; L., Tarozzi
abstract

In this paper, infrared thermography is used to measure the transient contact temperature between impinging droplets and hot solid surfaces. Droplets are released onto the heated solid surface of a barium fluoride (BaF2) disk, which has a high transmittance (about 90%) in the 8-12 m range (typical of longwave infrared cameras). The interface temperature is measured from below, through the solid material, by infrared thermography. Since the solid is IR-transparent, a black coating layer is used to allow radiative heating of the surface and provide a method to measure the liquid-solid interface temperature. A numerical code is then presented, which simulates the evaporation of water droplets on hot solid surfaces. At the present stage of development, single-phase evaporation is addressed. The three-dimensional energy diffusion equation, discretized using the finite volume method, is employed to model the transient within both the droplets and the solid substrate. The numerical results are validated by comparison with the experimental data.


2007 - Experimental tests of dropwise cooling on infrared-transparent media [Articolo su rivista]
L., Tarozzi; Muscio, Alberto; Tartarini, Paolo
abstract

The present work is aimed at analyzing the cooling of hot solid surfaces induced by liquid droplets. In particular, the study is focused on the non-intrusive measurement of the transient contact temperature between impinging droplets and hot solid surfaces.An experimental apparatus was built and set up in order to approach the non-trivial problem of the measurement of a solid–liquid interface temperature after droplet impingement. The solid–liquid interface temperature was monitored from below through a transparent-to-infrared material. That material had been coated with a very thin layer of high-emissivity, opaque paint on its upper side, so that it could effectively respond to the infrared camera located below.The paper reports the main results that have been collected to date, with particular regard to the approaches used to coat the transparent solid. Some considerations are also expressed about the effectiveness of the proposed method and about the improvements thatare currently being implemented to get new and more accurate interface temperature measurements.


2007 - Fuel cell systems and traditional technologies. Part I: Experimental CHP approach [Articolo su rivista]
Santangelo, Paolo Emilio; Tartarini, Paolo
abstract

One of the most innovative solutions concerning CHP for residential and industrial applications consists in using fuel cell devices. The importance of this technology is connected to the possibility of having a nearly complete energetic independence. A comparison between traditional systems for energy generation and co-generative fuel cell systems is needed to properly evaluate whether fuel cells could be a reasonable alternative to conventional systems.The present work describes the project of an experimental setup which is focused on testing the high temperature Solid Oxide FuelCells (SOFC) concept as a promising innovative system. The problem of planning facilities based on fuel cell devices is faced, and the still-to-be-solved question of thermal storage is addressed. The core of the work consists of a theoretical calculation and comparison of fuel consumption for both the fuel cell and traditional systems.


2007 - Investigation of surface cooling by droplet evaporation with IR infrared thermography [Relazione in Atti di Convegno]
L., Tarozzi; Muscio, Alberto; Tartarini, Paolo
abstract

In the present work infrared thermography is used to analyze the cooling effect of a hot solid surface induced by liquid droplets. In particular water droplets are released onto a BaF2 disk heated by radiation from above; the interface temperature is measured from below by means of an AVIO TVS500 infrared camera, carrying a micro-bolometric FPA sensor which operates in the long wave spectral range. The study is focused on the non-intrusive technique used to measure the transient temperature at the interface between impinging droplets and hot surface; experimental data are reported and compared with theoretical results.


2007 - Investigation of surface cooling by droplet evaporation with IR thermography [Relazione in Atti di Convegno]
L., Tarozzi; Muscio, Alberto; Tartarini, Paolo
abstract

In the present work infrared thermography is used to analyze the cooling effect of a hot solid surface induced by liquid droplets. In particular water droplets are released onto a BaF2 disk heated by radiation from above; the interface temperature is measured from below by means of an AVIO TVS500 infrared camera, carrying a micro-bolometric FPA sensor which operates in the long wave spectral range. The study is focused on the non-intrusive technique used to measure the transient temperature at the interface between impinging droplets and hot surface; experimental data are reported and compared with theoretical results.


2007 - Investigation of three-phase flow in horzontal pipes and its representation in ternary diagrams [Relazione in Atti di Convegno]
G., Sotgia; Stalio, Enrico; Tartarini, Paolo
abstract

The physical understanding of three-phase flow characteristics in horizontal pipes is of importance in the production of hydrocarbons from oil fields since very often oil, water, and natural gas flow together in the transporting pipelines. The work is focused on evaluating the effect of air injection on the pressure drop of a two-phase oil-water flow. Experiments reported are performed at the two-phase thermo-fluid dynamics laboratory of the Politecnico di Milano, using mineral oil and tap water of viscosity ratio about 800 and density ratio 0.9, together with ambient air. For the interpretation of the wide set of experimental data we use newly introduced, easily readable three-phase flow diagrams. In our experiments, the presence of air always has a negative effect on drag when it is injected into an oil-water flow in annular regime. Conversely, in the stratified regime, air supply at moderate flow rates can increase the drag reduction effect of water, but the stratified regime is not well suited for viscous oil transportation.


2006 - Droplets wall interaction: Measurement of the interface temperature through infrared-transparent media [Relazione in Atti di Convegno]
Tartarini, Paolo; Santangelo, Paolo Emilio; Tarozzi, Luca
abstract

A new, non-intrusive method is proposed to measure the solid-liquid contact temperature during dropwise evaporative cooling. The droplets are deposited onto a material, BaF2, which is transparent in the infrared spectral band. The transparent tile is coated with a very thin layer of high-emissivity, opaque paint on its upper side, so that it can effectively respond to the infrared camera below. The interface temperature can thus be measured through the solid material by a thermographic camera. Tests are carried out on the black painted BaF2 disk after its optimization by mechanical machining. The experimental tests are conducted following two deposition procedures: a) multi-droplet arrays, b) sprays. The two different behaviors and the corresponding cooling results are finally compared.


2006 - Dropwise evaporative cooling of a low thermal conductivity solid [Capitolo/Saggio]
Di Marzo, M.; Liao, Y.; Tartarini, P.; Evans, D.; Baum, H.
abstract

Insight on extinguishment of a solid fuel fire by sprinkler generated droplets is obtained by detailed modelling of a single droplet evaporative cooling on a hot low thermal conductivity solid. The assumption of constant and uniform temperature at the solid-liquid interface, which decouples the solid and the liquid modellmg, cannot be applied to this case because strong local cooling of the solid requires the solutions of both regions (liquid and solid) to be coupled. The large thermal gradients observed at the edge of the droplet preclude the application of finite difference techniques for the integration of the transient conduction governing equation. A mixed technique that uses a control volume method for the liquid and a boundary element formulation for the solid is proposed. Both methods are briefly outlined and the computed predictions are validated with experimental measurements which encompass high resolution thermography of the solid surface subjected to evaporative cooling. Insight on the temperature distribution at the solid-hquid interface is obtained deduced from the model and the deviation from the constant and uniform temperature at the liquid-solid interface is assessed. The radial versus axial conduction in the liquid droplet is also quantified.


2006 - From two phsae oil water to three phase oil/water/air flows in horizontal pipes: pressure drop and flow regimes. [Relazione in Atti di Convegno]
G., Sotgia; Stalio, Enrico; Tartarini, Paolo; A., Villa
abstract

The interest in oil-water pipe flow descends from its importance in petrochemical industries; pumping power requirements during oil transportation is considerably reduced in the core-annular flow regime. In petroleum transportation pipelines, an additional phase of natural gas frequently flows with the oil. The prediction of pressure drop and stability characteristics of the three-phase flow in these lines is important for proper operation of the transportation plants at reduced power consumption. Results from a set of experiments of three-phase flow of high viscosity oil, water and air in horizontal pipes of two different diameters are presented in the paper. Pressure drop measurements are related to three phase flow patterns observations in a defined range of specific flow rates of water, oil and air. When air is supplied in a wavy-stratified flow of oil and water, the presence of air plugs hinders stratification and ensures a lower resistance as respect the corresponding oil-water case; disturbances induced by the gaseous phase grow rapidly with increasing air specific flow rate and the tendency is reversed by a higer flow rate of air. The presence of air in an annular flow of oil induce large quasi-periodic deformations of the interface between oil and water and has a negative effect on drag.


2006 - Multi-droplet cooling: Experimental tests on infrared-transparent media [Relazione in Atti di Convegno]
Santangelo, Paolo Emilio; Tarozzi, Luca; Tartarini, Paolo
abstract

The present work is aimed at analyzing the cooling of hot solid surfaces induced by liquid droplets. In particular, the study is focused on the comparison between the cooling effects obtained with multiple droplets and sparse spray configurations.A new, non-intrusive measurement of the transient contact temperature between impinging droplets and hot solid surfaces is used and described. An experimental apparatus was built and set up in order to approach the non-trivial problem of the measurement of a solid-liquid interface temperature after droplet impingement. The solid-liquid interface temperature was monitored from below through a transparent-to-infrared material. That material had been coated with a very thin layer of high-emissivity, opaque paint on its upper side, so that it could effectively respond to the infrared camera located below.The paper reports the main results that have been collected to date, with particular regard to the approaches used to coat the transparent solid. Some considerations are also expressed about the effectiveness of the proposed method and about the improvements that are currently being implemented to get new and more accurate interface temperature measurements.


2005 - Dropwise cooling: experimental tests on infrared-transparent media [Relazione in Atti di Convegno]
L., Tarozzi; Muscio, Alberto; Tartarini, Paolo
abstract

The present work is aimed at analyzing the cooling of hot solid surfaces induced by liquid sprays. In particular, the study is focused on the measurement of the transient contact temperature between impinging droplets and hot solid surfaces.An experimental apparatus was built and setup in order to approach the non-trivial problem of the non-intrusive measurement of a solid-liquid interface temperature after droplet impingement. The solid-liquid interface temperature was monitored from below through a transparent-to-infrared, zero-emissivity material. That material had been coated with a very thin layer of high-emissivity, opaque paint on its upper side, so that it could effectively respond to the infrared camera located below.The experiences collected up to now are described, with particular regard to the approaches used to coat the transparent solid. The results of a few preliminary tests are also reported here, together with considerations about the effectiveness of the proposed method and about the improvements that are currently being implemented to get new and more accurate interface temperature measurements. The obtained results are comparable with the predictions of the theoretical contact temperature equation, which is available in literature.


2005 - I cool roofs, una soluzione innovativa per il risparmio energetico in edilizia [Relazione in Atti di Convegno]
Barozzi, Giovanni Sebastiano; Corticelli, Mauro Alessandro; Muscio, Alberto; Tartarini, Paolo
abstract

I cool roofs sono tetti contraddistinti da elevata capacità di riflettere l’irradiazione solare incidente e, al contempo, di emettere energia termica nell’infrarosso. Essi possono fornire un’efficace soluzione al problema del surriscaldamento estivo dei singoli edifici e delle grandi aree urbane.In California e in altri Stati degli U.S.A. i cool roofs sono da molti anni oggetto di analisi tecnico-economiche estensive e, più recentemente, di attività di certificazione e regolamentazione. In Italia, invece, sebbene le condizioni climatiche di buona parte della penisola siano tali da rendere conveniente l’installazione di cool roofs, questi sembrano sconosciuti ai più. Studi in materia sono stati perciò avviati dal Dipartimento di Ingegneria Meccanica e Civile di Modena.In questa relazione si illustra il funzionamento dei cool roofs dal punto di vista fisico. In particolare, si analizzano gli effetti che le diverse proprietà emissive hanno sulle temperature raggiunte dal tetto e sul calore che lo attraversa. Si delineano inoltre i principali programmi di attestazione delle proprietà e di incentivazione avviati degli U.S.A. e la situazione di mercato.


2005 - Radiative properties of Surfaces and energy saving in buildings: the cool roofs [Relazione in Atti di Convegno]
Barozzi, Giovanni Sebastiano; Corticelli, Mauro Alessandro; Muscio, Alberto; L., Tarozzi; Tartarini, Paolo
abstract

Cool roofs are building coverings having high reflectance to solar radiation and high emittance in the infrared range. They can provide an effective solution to building overheating during hot seasons.In the U.S.A. the cool roofs have been investigated extensively. Certification procedures have also been developed by independent bodies, and certified roof products are commercially available.In the aim of verifying the potential of cool roof technologies for the Italian climate, an investigation was started at the Dept. of Mechanical and Civil Engineering at Modena.Early results are presented for an experimental cool roof. The work is completed with an analysis of the thermal behavior of a typical low-slope roof and a brief review of existing certification programs and commercially available products.


2005 - Thermographic measurement of the solid-liquid interface temperature through infrared-transparent media [Relazione in Atti di Convegno]
Tartarini, Paolo; Muscio, Alberto; L., Tarozzi
abstract

A new, non-intrusive method is proposed to measure the solid-liquid contact temperature duringdropwise evaporative cooling. The droplets are deposited onto a material which is transparentin the infrared spectral band. The interface temperature can thus be measured through the solidmaterial by a thermographic camera. The transparent tile is coated with a very thin layer ofhigh-emissivity, opaque paint on its upper side, so that it can effectively respond to the infraredcamera below.


2004 - Rarefaction Effect on Friction Factor of Gas Flow in Microchannels [Articolo su rivista]
G. L., Morini; M., Spiga; Tartarini, Paolo
abstract

Microfluidic devices are used today in many engineering applications. However, despite much progress in this field, the fundamental understanding of fluid flow and heat transfer on the microscale is still not satisfactory. In this study, the rarefaction effects on the pressure drop for an incompressible flow through silicon microchannels having a rectangular, trapezoidal or double-trapezoidal cross-section are investigated. The roles of the Knudsen number and the cross-section aspect ratio in the friction factor reduction due to the rarefaction are pointed out.


2004 - The problem of the contact temperature in droplet-solid heat transfer: experimental analysis [Relazione in Atti di Convegno]
Muscio, Alberto; G., Tambascia; Tartarini, Paolo
abstract

The present work is aimed at analyzing the cooling of hot solid surfaces induced by liquid sprays. In particular, the study is focused on the measurement of the transient contact temperature between impinging droplets and hot solid surfaces.An experimental apparatus was built and setup in order to approach the non-trivial problem of the non-intrusive measurement of a solid-liquid interface temperature after droplet impingement. The solid-liquid interface temperature was monitored from below through a transparent-to-infrared, zero-emissivity material. That material had been coated with a very thin layer of high-emissivity, opaque paint on its upper side, so that it could effectively respond to the infrared camera located below.The experiences collected up to now are described, with particular regard to the approaches used to coat the transparent solid. The results of a few preliminary tests are also reported here, together with considerations about the effectiveness of the proposed method and about the improvements that are currently being implemented to get new and more accurate interface temperature measurements. The obtained results are comparable with the predictions of the theoretical contact temperature equation, which is available in literature.


2003 - Analisi CFD dei campi di moto e di temperatura dell'aria in una cattedrale [Relazione in Atti di Convegno]
Corticelli, Mauro Alessandro; Muscio, Alberto; Tartarini, Paolo
abstract

Nel presente lavoro viene proposta un’indagine teorica e numerica sul campo di moto e sulla distribuzione della temperatura dell’aria all’interno della National Shrine of the Immaculate Conception, una cattedrale di imponenti proporzioni situata nel campus della Catholic University of America a Washington, D.C., U.S.A.Lo studio è finalizzato a valutare differenti modalità di riscaldamento dell’ambiente interno della cattedrale, e trae motivazione dal gran numero di edifici per il culto che presentano dimensioni e caratteristiche simili e dall’esigenza diffusa di ottimizzarne gli impianti di climatizzazione, in termini di benessere delle persone e di risparmio energetico.Dal punto di vista teorico, si propone un’analisi adimensionale del problema, basata sul numero di Rayleigh. Le simulazioni numeriche sono effettuate mediante il codice CFD industriale Fluent, prodotto da Fluent Inc., Lebanon, N.H., U.S.A.


2003 - Experimental Analysis of Flow Regime Trasnitions and Pressure Drop Reductions in Oil-Water Mixtures [Relazione in Atti di Convegno]
M. S., Mello; G., Sotgia; Tartarini, Paolo
abstract

The present work reports an experimental and theoretical analysis of the fluid dynamic behavior of oil-water systems flowing through horizontal ducts. In the frame of an ongoing research program, new experimental tests are conducted on smooth, horizontal tubes of Pyrex and Plexiglas. Tap water and mineral oil are used, with a viscosity ratio of about 800 and a density ratio of about 0.9. The resulting database, which includes previous test findings, covers a tube diameter range spanning from 21 to 40 mm. The influence of different parameters on the pressure drop in oil-water flows is evaluated, and some particular behaviors of the pressure drop reduction as a function of the water volume fraction are observed. Flow pattern maps are obtained, which report consistent results of the experimental campaign in terms of flow regimes and transitions. A theoretical analysis based on both Froude and Reynolds numbers is also proposed.


2003 - Theoretical and Numerical Study on Dropwise Cooling under Nucleate Boiling Conditions [Relazione in Atti di Convegno]
C., Bussi; Muscio, Alberto; Tartarini, Paolo
abstract

In this work, a theoretical model has been formulated and a numerical code has been developed to analyze the cooling effect induced by liquid droplets during single-phase evaporation and nucleate boiling regime on high temperature solid surfaces.The model is based on a numerical integration of the energy and mass conservation equations in the solid and the liquid domain. In terms of geometry discretization, a cylindrical coordinate system is used, and the differential equations are modeled on an axis-aligned half plane. Evaporation of liquid is reproduced at either the solid-liquid or the liquid-air interfaces.The non-linear system of partial differential equations is discretized using an iterative, second-order in time and space, semi-implicit scheme. A fast sparse solver is used to obtain energy and mass variations with respect to time. Experimental results are finally employed to tune and validate the model.


2001 - Measurement of the thermal diffusivity of thin slab specimens by the lock-in heating-cooling method [Relazione in Atti di Convegno]
Muscio, Alberto; F., Gavelli; Tartarini, Paolo
abstract

The present work describes a new test method for the in-situ non-destructive measurement of the thermal diffusivity of solid materials.A periodic thermal disturbance is supplied to the inspected material by a thermoelectric source based on the Peltier effect. This procedure alternates heating and cooling stages and provides, if properly controlled, a harmonic perturbation with null net heat flux. Thus, a steady-periodic temperature field can be induced within the specimen. The diffusivity of the material is estimated by monitoring the propagation of the temperature cycles along the optically-accessible surface of the specimen, adjacent to the thermal input surface area. A digital camera for infrared thermography is used to obtain non-intrusive surface temperature measurements.At the current stage of development, the focus is on an accurate reproduction of the theoretical model on which the method is based. Ease of operation and portability of the test equipment are also pursued. This notwithstanding, early tests on thin specimens of known materials have given results in encouraging agreement with the nominal values.


2001 - Numerical simulation of the cooling effect of multiple droplets on a hot solid surface [Relazione in Atti di Convegno]
Muscio, Alberto; F., Gavelli; Tartarini, Paolo
abstract

A numerical code is presented that simulates the evaporation of water droplets on hot solid surfaces. The surface temperature conditions are such that only single-phase evaporation is obtained. The two-dimensional, axial-symmetrical energy diffusion equation, discretized with the finite volume method, is used to model the transient within both the droplets and the solid substrate.The current work simulates the substrate cooling effect due to a multi-droplet system, made of a ring of six identical droplets surrounding a central one. The overall transient is obtained by superposition of effects, from the solution for the axial-symmetrical substrate temperature field due to the evaporation of an individual droplet. The numerical results are validated by comparison with experimental data.The code is implemented in Matlab, using a modular and flexible architecture. This will allow the expansion of the code to simulate convective motion and nucleate boiling in the droplet, as well as other fluids.


2000 - Cooling of hot ceramic surfaces induced by water sprays in the nucleate boiling regime [Relazione in Atti di Convegno]
Tartarini, Paolo; Muscio, Alberto
abstract

An experimental and theoretical research is conducted, focusing on the thermal behavior of hot, non-porous, low-conductivity surfaces during the cooling transient induced by single- and multi-droplet boiling water systems. The research is aimed at modeling the cooling effect induced on a hot solid surface by sprinkler-generated droplets. The long term objective of this study is the construction of a model for the prediction and optimization of the performance of sprinkler-based fire-extinguishment systems. In this paper, the results of a series of experimental tests on single- and multi-droplet boiling systems are presented and discussed. The main objectives of the present study are: a) to investigate experimentally the effect of the boiling onset on the cooling effect induced on the solid surface by the water droplets; b) to measure the evolution of the solid surface temperature during evaporation, with particular attention to the values of minimum, maximum and average temperature; c) to examine the possibility of improving spray cooling efficiencies.


2000 - On-site measurement of thermal diffusivity by infrared thermography and thermoelectric equipment [Relazione in Atti di Convegno]
Muscio, Alberto; F., Gavelli; Tartarini, Paolo
abstract

The latest advancements are presented about a new method to quantify the thermal diffusivity, devised for on-site measurements of solids accessible from one side only.A periodic thermal input is supplied to the inspected solid by a thermoelectric device based on the Peltier effect, which can alternate heating and cooling stages and quickly produce a steady-periodic temperature field within the solid, with null net heat input. The diffusivity of the material is then estimated by monitoring the propagation of the temperature cycles along the accessible surface of the solid, adjacent to the thermal input area. A portable camera for infrared thermography is used for non-intrusive surface temperature measurement.Mathematical and experimental methods are utilised to identify the conditions for which a 1D heat transfer model can be used to accurately represent the actual 3D temperature field. At the present stage, the attention is focused onto obtaining the adherence of the test system to the theoretical model. Ease of operation and portability of the equipment are also pursued.


2000 - The influence of nucleate boiling regime on dropwise cooling of low-conductivity surfaces [Relazione in Atti di Convegno]
Tartarini, Paolo; Muscio, Alberto
abstract

An experimental and theoretical research is conducted, focusing on the thermal behavior of hot, non-porous, low-conductivity surfaces during the cooling transient induced by single- and multi-droplet boiling water systems. The research is aimed at modeling the cooling effect induced on a hot solid surface by sprinkler-generated droplets. The long term objective of this study is the construction of a model for the prediction and optimization of the performance of sprinkler-based fire-extinguishment systems. in this paper, the results of a series of experimental tests on single- and multi-droplet boiling systems are presented and discussed. The effect of the boiling onset on dropwise cooling is investigated, and the possibility of improving spray cooling efficiency is examined.


2000 - Theoretical, numerical and experimental investigation of a one-side measurement technique for thermal diffusivity [Relazione in Atti di Convegno]
Muscio, Alberto; Corticelli, Mauro Alessandro; Tartarini, Paolo
abstract

A modified Angstrom’s method for the measurement of thermal diffusivity in solid materials is presented, aimed at overcoming the limits of ordinary techniques with one-side measurements. The method requires a periodic thermal input to be supplied to the specimen, alternating heating and cooling stages. The thermal diffusivity is estimated by monitoring the temperature oscillations on the free surface of the specimen.The conditions at which a real three-dimensional test-system can be studied by means of a one-dimensional thermal model are investigated. Algorithms to estimate the thermal diffusivity are determined analytically and verified by numerical simulation. The method is finally validated by experimental measurements.


1999 - Experimental study of water droplet boiling on hot, non-porous surfaces [Articolo su rivista]
Tartarini, Paolo; G., Lorenzini; M. R., Randi
abstract

In this paper, the results of a series of experimental tests on single- and multi-droplet boiling systems are presented and discussed. The main objectives of the present study are: a) to investigate experimentally the effect of the boiling onset on the evaporation rate of water droplets; b) to measure the evolution of the solid surface temperature during evaporation; c) to examine the possibility of improving spray cooling efficiencies. The behavior of small water droplets (from 10 to 50 mu l) gently deposited on hot, non-porous surfaces is observed. The evaporation of multi-droplet arrays (50 and 100 mu l) under the same conditions of the single-droplet tests is analyzed. In particular, the conditions which determine the onset of nucleate and film boiling are stressed out. In the experimental tests, the interaction of different materials with several multi-droplet systems is monitored by infrared thermography. The spray cooling efficiency is related to the solid temperature decrease as a function of the water mass flux. In the present study, the effect of varying the droplet volume and the mass flux is also analyzed and discussed. The results on the droplets evaporation time and on the solid surface transient temperature distribution are also compared with the data obtained by the same authors during the analysis of droplet evaporation in total absence of nucleate and film boiling. In order to analyze the different behavior of the evaporating droplet as a function of the solid surface thermal conductivity, evaporative transients on aluminum, stainless steel and macer (a glass-like, low-conductivity material) are considered.


1999 - Numerical investigation of a one-side measurement technique for thermal diffusivity [Relazione in Atti di Convegno]
Barozzi, Giovanni Sebastiano; Corticelli, Mauro Alessandro; Muscio, Alberto; Tartarini, Paolo
abstract

A modified Angstrom’s method for the measurement of the thermal diffusivity of solid materials is presented, aimed at overcoming the limits of ordinary one-side techniques. The method requires a periodic thermal input, alternating heating and cooling stages, to be supplied to the specimen. The thermal diffusivity is estimated by monitoring the temperature oscillations on the free surface of the specimen.The conditions for which a real three-dimensional test-system can be studied by means of a one-dimensional thermal model are investigated by analytical and numerical methods. The algorithms for the estimate of thermal diffusivity are determined for the one-dimensional thermal system and are verified by numerical simulation. The applicability of the algorithms to multi-dimensional configurations is finally explored.


1999 - Photographic investigation of water droplet impingement and boiling on hot surfaces [Relazione in Atti di Convegno]
Barozzi, Giovanni Sebastiano; Corticelli, Mauro Alessandro; Muscio, Alberto; Tartarini, Paolo
abstract

The present research is aimed at analyzing the behavior of small water droplets impinging, with different Weber numbers, on hot, non-porous surfaces. An experimental and theoretical study is conducted, focusing on the influence of the Weber number on the cooling effects induced by droplet impingement and evaporation in presence of nucleate boiling. In order to get more insight into the phenomenon, the droplets behavior is monitored by a high-speed video-camera, and the influence of the Weber number on dropwise evaporative cooling is analyzed. In particular, the conditions which determine the onset of nucleate boiling are emphasized, and the solid surface cooling transients are also monitored via infrared thermography.


1999 - Thermographic investigation of water droplet boiling on hot ceramic surfaces [Relazione in Atti di Convegno]
Corticelli, Mauro Alessandro; Muscio, Alberto; Tartarini, Paolo
abstract

An experimental research is conducted, focusing on the thermal behavior of hot, non-porous, ceramic surfaces during the cooling transient induced by single- and multi-droplet boiling water systems. The research is aimed at modeling the extinguishment of a solid fuel fire by sprinkler-generated droplets. The long term objective of this study is the construction of a model for the prediction and optimization of sprinkler-based extinguishment systems performance. In this paper, the results of a series of experimental tests on single- and multi-droplet boiling systems are presented and discussed. In order to get more insight into the solid surface temperature transients induced by dropwise evaporation and boiling, the test materials have been chosen within the category of low thermal conductivity substances (1 to 5 W m-1 °C-1), so that a relevant and well-measurable cooling effect is observed. The dropwise cooling transients are monitored by the non-intrusive method of infrared thermography, and the potentialities of this approach are stressed out.


1999 - Water Droplet Boiling on Hot, Non-Porous Ceramic Surfaces [Articolo su rivista]
BAROZZI, Giovanni Sebastiano; CORTICELLI, Mauro Alessandro; T. R., Maciver; TARTARINI, Paolo
abstract

In this study, an experimental research is conducted, analyzing the behavior of small water droplets (from 10 to 50 :l) gentlydeposited (the Weber number is less than 13) on hot, non-porous, ceramic surfaces. In particular, the conditions whichdetermine the onset of nucleate boiling are emphasized, and the solid surface cooling is monitored via infrared thermography.The results, mainly concerning the evaporation time of the droplets and the solid surface transient temperature distribution,provide some insight into the mechanisms of dropwise evaporative cooling in presence of nucleate boiling. The non-intrusive method of infrared thermography is also used to study the peculiar thermal behavior of industrial ceramic surfaces subjected to high heating fluxes. Dropwise evaporation under boiling conditions is showed to be an effective method to cool down even non-uniform-temperature ceramic tiles.


1998 - Laminar Viscous Dissipation in Rectangular Ducts [Articolo su rivista]
G. L., Morini; M., Spiga; Tartarini, Paolo
abstract

In this paper, a theoretical study is conducted, calculating the temperature distn'bution in the cross-section of a rectangular duct, under the conditions of newtonian and incompressa'ble fluid, fully developed laminar flow and steady-state regime. The governing equations are solved resorting to the finite Fourier transfornl The temperature distn'butions are obtained. The results concerning the temperature dism'bution in a square duct are shown by tables and figures, and a comparison between the present solution and some literature conm'butions is also presented. The viscous dissipation is responsible for a power generation that, for a particular Brinkman number (Brq = 1/Phi* or Brw=+-infinity), allows the wall heat flux to vanish. At last, the effects of viscous dissipation and wall heat flux are presented in some graphs, as a function of the duct aspect ratio.


1998 - Water droplet boiling on hot, non-porous, ceramic surfaces [Relazione in Atti di Convegno]
Barozzi, Giovanni Sebastiano; Corticelli, Mauro Alessandro; T. R., Maciver; Tartarini, Paolo
abstract

An experimental research is conducted analysing the behaviour of small water droplets (10-15 microliters) gently deposited on hot non-porous ceramic surfaces. In particular the conditions determining the onset of nucleate boiling are emphasized, and solid surface cooling is monitored via infrared thermography. The results provide insight into the mechanisms of dropwise evaporative cooling in presence of nucleate boiling. THe non-intrusive method of thermography is also used to study the peculiar thermal behavior of industrial ceramic surfaces subjected to high heat fluxes.


1997 - Flooding Criterion for Evaporative Cooling on Horizontal Semi-Infinite Solids [Articolo su rivista]
M., Lederer; M., di Marzo; TARTARINI, Paolo
abstract

The evaporative cooling of a sparse spray impacting on a hot solid is investigated to determine the limiting condition associated with the liquid flooding of the solid surface. The flooding condition is identified when the evaporation rate is insufficient to remove the amount of water being deposited on the surface. The flooding criterion is derived as a function of the initial single droplet volume prior to deposition, the Evaporation-Recovery Cycle (ERC) and the area of influence, which describes the region of the solid surface associated with a single droplet cooling effect. These last two quantities, the ERC and the area of influence, are evaluated by integrating previously obtained theoretical and experimental information with selected experimental data obtained in this study. The flooding criterion, while semi-empirical in its derivation, can be generalized to all non-porous solids under a variety of conditions. The spray is sparse and the water droplets are considered of uniform size. Extension to a spray with non-uniform droplet distribution is not considered here.


1997 - Numerical solution of dropwise evaporative cooling [Relazione in Atti di Convegno]
Tartarini, P.; Di Marzo, M.
abstract

A numerical code for the prediction of evaporative cooling of solid surfaces induced by gently deposited water droplets is presented. The code is based upon a solid-liquid coupled model which predicts the droplet evaporation and the solid surface cooling for materials with thermal conductivity spanning over more than two orders of magnitude. Surface heating by conduction and radiation is considered. The numerical solution of the heat-conduction equation, which links a control volume method (CVM) used for the liquid and a boundary element method (BEM) used for the solid, is presented. By comparing the numerical predictions with available experimental data, the single-droplet code is validated and used as a basis to formulate the multi-droplet model, which is also presented.


1996 - Effect of Liquid-Solid Contact Angle on Droplet Evaporation [Articolo su rivista]
S., Chandra; M., di Marzo; Y. M., Qiao; Tartarini, Paolo
abstract

The effect of varying initial liquid-solid contact angle on theevaporation of single droplets of water deposited on a stainless steel surface is studied using both experiments and numerical modeling. Contact angle is controlled in experiments by adding varying amounts (100 and 1000ppm) of a surfactant to water. The evolution of contact angle and liquid-solid contact diameter is measured from a video record of droplet evaporation. The computer model is validated by comparison with the experimental results. Reducing the contact angle increases the contact area between the droplet and solid surface, and also reduces droplet thickness, enhancing heat conduction through thedrop,!et. Both effects increase the droplet evaporation rate. Decreasing the initial contact angle from 90 to 20 ° reduces droplet evaporation time by approximately 50%. The computer model is used to calculate surface temperature and heat flux variation during droplet evaporation: adding 1000ppm of surfactant to the droplet is shown to enhance surfacecooling by up to 110%.


1996 - Evaporazione a gocce. Parte I: analisi sperimentale [Articolo su rivista]
Tartarini, Paolo
abstract

Nel presente lavoro sono esposti gli sviluppi ed i risultati di una ricerca condotta in forma sperimentale, teorica e numerica sul fenomeno dell' evaporazione a gocce. Tale ricerca, svolta in collaborazione con il Dipartimento di Ingegneria Meccanica dell' Università del Maryland (U.S.A.), ha coperto un arco di tempo di circa sei anni, ed alcune sue parti sono tuttora in corso. Pertanto, la presentazione del lavoro compiuto e dei risultati ottenuti è stata suddivisa in tre parti, che coincidono in larga parte con le tre fasi cronologiche della ricerca. Nella prima parte (relazionata nel presente articolo) sono descritti i metodi, gli apparati ed i risultati della fase sperimentale. Nella seconda parte verranno presentate le metodologie di approccio teorico ed il codice di calcolo con cui è stata effettuata la simulazione numerica dei fenomeni analizzati. Nella terza parte, infine, verranno presentati gli sviluppi della ricerca relativi all'estensione delle analisi dai sistemi a goccia singola a quelli multigocce (spray).


1996 - Evaporazione a gocce. Parte II: analisi teorica e numerica [Articolo su rivista]
Tartarini, Paolo
abstract

Nel presente articolo viene presentata la seconda parte di un lavoro sviluppato in forma sperimentale, teorica e numerica sul fenomeno dell'evaporazione a gocce. La parte sperimentale della ricerca è stata esposta in precedenza, e qui si descrive l'approccio teorico, costituito da un modello matematico basato su un metodo di calcolo agli elementi di contorno (Boundary Element Method) accoppiato con metodo integrale ai volumi di controllo (Control Volume Method). Viene inoltre descritto il codice di calcolo in cui il modello matematico è stato implementato, e i risultati della simulazione numerica vengono confrontati con i dati sperimentali ottenuti in precedenza. Si osserva come la simulazione numerica permetta di calcolare con grande precisione i tempi di evaporazione di singole gocce d'acqua che evaporano su superfici calde di conducibilità termica estrememente diversa tra loro. Inoltre si riscontra come i risultati teorico-numerici siano in eccellente accordo con i dati sperimentali anche per ciò che riguarda la determinazione della distribuzione di temperatura sulla superficie solida raffreddata durante il transitorio di evaporazione.


1994 - Analisi Numerica della Propagazione di Onde di Pressione in Gallerie Ferroviarie [Articolo su rivista]
Tartarini, Paolo; F., Gavelli; G., Lorenzini
abstract

Lo scopo del presente lavoro è quello di analizzare il fenomeno della propagazione delle onde di pressione in una galleria ferroviaria in seguito al transito di un convoglio. Il problema viene esaminato in analogia con il moto di un pistone in un cilindro a tenuta imperfetta ed aperto ad entrambe le estremità. Il modello teorico si basa su un flusso monodimensionale non stazionario, completato da un'analisi più dettagliata di alcune regioni (le estremità del treno e della galleria) in cui tale approssimazione risulta inaffidabile. Queste zone vengono trattate come discontinuità del campo aerodinamico e forniscono le condizioni al contorno per le varie parti in cui esse suddividono il dominio monodimensionale; su quest'ultimo vengono risolte le equazioni che governano il problema mediante un codice alle differenze finite. I risultati ottenuti sono posti a confronto con alcuni dati sperimentali relativi a gallerie della tratta Firenze-Roma. Vengono inoltre presentati dei grafici che correlano l'intensità dei fenomeni aerodinamici in funzione di alcuni parametri, quali la velocità del convoglio ed il suo profilo aerodinamico.


1994 - Numerical analysis of compact air condensers [Articolo su rivista]
Tartarini, Paolo; E., Lorenzi; G. L., Morini
abstract

The present work aims at analysing the thermal behaviour of the vapour flow inside the horizontal tube bundle of a cross-flow air condenser. It is pointed out that the steady-state air and watertemperature distribution cannot be determined by means of analytical solutions, due to the non-linearity of the problem. A model based on appropriate balance equations is introduced and a finite difference computer code is formulated. This code, which reports a large number of correlations found in the literature, is used to evaluate the different flow patterns that characterise the two-phase flow condensation. It is also employed to calculate the local heat transfer coefficient, for both air and water side, and thepressure drop on the water side. The main results, related to the evaluation of the condenser's thermal-hydraulic behaviour (pressure and temperature of the condensing fluid), are presented and discussed in detail.


1993 - Evaporative Cooling Due to a Gently Deposited Droplet [Articolo su rivista]
M., di Marzo; Tartarini, Paolo; Y., Liao; D., Evans; H., Baum
abstract

The transient thermal behavior of a single water droplet gently deposited on the surface of a semi-infinite solid is investigated. A coupled model that solves simultaneously the transient conductionequation for the solid and the liquid to yield the surface temperature and heat flux distributions as well as the description of the droplet evaporation transient is proposed. The predictions of the evaporation time are compared with experimental data. An additional model is presented which assumes constant heat fluxat the liquid-solid interface. This model provides a closed form solution for the solid surface transient temperature distribution.


1993 - Numerical simulation of multi-droplet evaporative cooling [Articolo su rivista]
Tartarini, P.; Liao, Y.; di Marzo, M.
abstract

A theoretical study is carried out to predict the thermal behavior of a solid surface subjected to multi-droplet evaporative cooling. A single-droplet numerical code, which has been previously presented and validated, is used here to gain insight into the behavior of a surface subjected to dropwise evaporative cooling. On the basis of the single-droplet results, a generalized model is presented and a novel numerical code is formulated, which analyzes the effects of a multi-droplet evaporative transient on a low thermal conductivity solid surface. The main parameters that characterize the evaporative transient behavior are identified. Some numerical results obtained with this new model are presented and discussed.


1992 - Experimental and theoretical investigation of a tube-bundle heat exchanger [Relazione in Atti di Convegno]
Lorenzini, E.; Orlandelli, C. M.; Spiga, M.; Tartarini, P.
abstract

This paper presents the experimental data concerning the temperature distribution in a single pass crossflow heat exchanger, where hot water flowing in a tube bundle is cooled by air. The lower region of the facility works as a crossflow heat exchanger with unmixed fluids; here the analytical investigation is carried out by solving the energy balance equations (for air, water and walls) resorting to the two-fold application of the Laplace transform technique. The upper part of the exchanger, where air flows in the shell side through the tube bundle without water flow, is simulated as a packed bed. The temperature distribution is obtained by solving the coupled partial differential equations governing air and copper temperature. At last the experimental data and the analytical results are compared and discussed, stressing the effects of the main physical and geometrical parameters on the heat exchanger behavior.


1992 - Infrared Thermography of Dropwise Evaporative Cooling of a Semi-Infinite Solid Subjected to Radiant Heat Input [Articolo su rivista]
M., di Marzo; C., Kidder; Tartarini, Paolo
abstract

A single droplet is gently deposited on the surface of a semi-infinite body and the evaporative cooling transient is recorded. This study is limited to the evaporative phenomena, therefore, the temperature range selected is such that nucleate boiling or film boiling are not observed. The solid (a glass-like material) is heated from above by two radiant electric panels and it is placed on a chilled plate held at near ambient, constant and uniform temperature. The transient temperature distribution over the semi-infinite solid surface is monitored by infrared thermography. Image processing techniques are used to eliminate undesired information and to retain the data which are then converted into surface temperature readings. Droplet sizes in the range of 10 to 50 μl are used with initial solid surface temperatures between 90 and 180 ̊C. The results are compared with similar experiments performed with the semi-infinite solid heated from below by conduction to gain insight into the competing mechanisms of evaporation by direct radiation from above and by conduction at the solid-liquid interface. The droplet aspect ratio is a dominant parameter in the conduction controlled evaporative component. Therefore, particular care is taken in assessing the behavior of the droplet shape during the transient. The direct radiation from above strongly reduces the surface tension of the liquid and thus allows the drop to spread on the surface more than for the conduction case.


1992 - Scaling of the High Pressure Injection in integral test facilities [Articolo su rivista]
Di Marzo, M.; Almenas, K.; Hsu, Y. Y.; Tartarini, P.; Heper, H.
abstract

Small Break LOCA (SB-LOCA) transients are compared to illustrate and validate a scaling methodology for reduced pressure integral facilities. This methodology is extended to include the analysis of the High Pressure Injection (HPI) boundary conditions. The tests are conducted in the MIST full pressure, full height facility and in the UMCP reduced pressure, reduced height facility. Two main parameters are chosen: the system inventory as a chronological scale and the normalized pressure as the parameter which represents the system behavior. The normalized results presented demonstrate that, for a SB-LOCA where the fluid leaving the system is subcooled, it is possible to scale a full pressure transient from tests conducted in a reduced pressure facility, with great advantages in terms of costs and time of analysis.


1992 - Solid-liquid interfacial conditions for dropwise evaporative cooling [Articolo su rivista]
Tartarini, P.; di Marzo, M.
abstract

A theoretical research is carried out to describe the thermal behavior of a solid surface subjected to droplet evaporative cooling. The objective of this study is the analysis of various simplified boundary conditions which can be used to generate predictions of the thermal behavior of the solid surface. This study is part of a more general research conducted in order to individuate the global cooling effect of a spray impinging a hot solid surface. A number of numerical algorithms are used to obtain solutions of the governing equations for the various cases examined. Results are presented for the different boundary conditions.


1991 - Dropwise evaporative cooling [Relazione in Atti di Convegno]
di Marzo, M.; Tartarini, P.; Liao, Y.; Evans, D.; Baum, H.
abstract

A comprehensive model for the prediction of evaporative cooling of solid surfaces induced by the impingement of single water droplets is presented. The model predicts the droplet evaporation and the solid surface cooling for materials with thermal conductivity spanning over more than two orders of magnitude. The model accurately predicts the total evaporation time and it is further validated with transient surface temperature measurements obtained by infrared thermography. The predictions are in excellent agreement with the experimental data. The spatial and temporal heat flux distribution under the evaporating droplet is studied. The extent of the droplet evaporative cooling is quantified by introducing a novel concept defining the droplet radius of influence. A closed form solution predicting the radius of influence is derived and tested against the experimental data and the model predictions. An empirical correlation for the prediction of the evaporation time is also presented. Insight into the evaporative cooling phenomena is provided for materials with various thermal conductivity. The relevant parameters are identified and their influence on the phenomena is assessed.


1990 - An Improved Version of the Bacchus Code for the Analysis of Fuel Bundles [Articolo su rivista]
E., Lorenzini; F., Norelli; C. M., Orlandelli; M., Spiga; Corticelli, Mauro Alessandro; Tartarini, Paolo
abstract

The present work describes an improved version of the computer code BACCHUS-T to analyse the thermohydraulic features of the coolant flow in the fuel bundle of a LMFBR.The improvement mainly consists in the development of a numerical algorithm, based on the finite element method, in order to predict the temperature distribution in the fuel, gap and cladding regions, in transient conditions. Also mechanical and thermoelastic stresses can be determined.