Paolo Emilio SANTANGELO - personale UniMoRe

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Paolo Emilio SANTANGELO

Professore Associato
Dipartimento di Scienze e Metodi dell'Ingegneria

Pubblicazioni

2024 - Comprehensive modeling of ventilation systems for Nearly Zero Energy Buildings [Relazione in Atti di Convegno]
Sedoni, Roberto; Cannistraci, Gioele; Santangelo, Paolo Emilio; Angeli, Diego; Romani, Marco; Fioravanti, Luca
abstract

In the present work, a lumped-parameter model of a multifunctional ventilation unit for residential applications was developed in the Simulink environment, also relying on the Simscape toolbox with Moist Air and Two-phase fluid libraries. A simple, yet effective method to analyze and optimize the efficiency of the combined HVAC – air distribution system is proposed. To investigate the impact of boundary conditions on system performance, a parametric study of different installation conditions was also carried out, including outdoor air and indoor air temperature, humidity, static pressure, filter fouling, pressure drop in the intake and distribution ducts. The model highlights a strong decrease in the useful cooling/heating heat flow rate produced by the system as the installation and maintenance conditions become more challenging.

2023 - A critical review of Polymer Electrolyte Membrane Fuel Cell systems for automotive applications: Components, materials, and comparative assessment [Articolo su rivista]
Pedicini, Rolando; Romagnoli, Marcello; Santangelo, Paolo Emilio
abstract

The development of innovative technologies based on employing green energy carriers, such as hydrogen, is becoming high in demand, especially in the automotive sector, as a result of the challenges associated with sustainable mobility. In the present review, a detailed overview of the entire hydrogen supply chain is proposed, spanning from its production to storage and final use in cars. Notably, the main focus is on Polymer Electrolyte Membrane Fuel Cells (PEMFC) as the fuel-cell type most typically used in fuel cell electric vehicles. The analysis also includes a cost assessment of the various systems involved; specifically, the materials commonly employed to manufacture fuel cells, stacks, and hydrogen storage systems are considered, emphasizing the strengths and weaknesses of the selected strategies, together with assessing the solutions to current problems. Moreover, as a sought-after parallelism, a comparison is also proposed and discussed between traditional diesel or gasoline cars, battery-powered electric cars, and fuel cell electric cars, thus highlighting the advantages and main drawbacks of the propulsion systems currently available on the market.

2023 - A lumped-parameter model of a smart ventilation unit for Nearly Zero Energy Buildings [Relazione in Atti di Convegno]
Sedoni, Roberto; Cannistraci, Gioele; Santangelo, Paolo Emilio; Angeli, Diego; Romani, Marco; Fioravanti, Luca
abstract

In the present work, a simple model of a ventilation unit used for residential purposes is proposed, which was developed by means of MATLAB Simulink and the Simscape toolbox, also including the Moist Air and Two-Phase fluid libraries. This study falls in the realm of air conditioning in nearly Zero Energy Buildings. The model presented here is focused mostly on the aeraulic system. A parametric analysis of various installation conditions was conducted to assess and enhance the combined heat pump and the air distribution system performance, under various operating conditions. Therefore, the overall approach included several parameters, such as outdoor and indoor air temperature, humidity, static pressure, pressure drop in the intake and the distribution ducts, and filter fouling. The model serves as a predictive tool to evaluate the effectiveness of the whole system, in both design and off-design conditions; notably, critical conditions are emphasized, which are associated to severe fouling conditions, making the use of an additional fan ineffective.

2023 - Advanced simulation of nitrogen cooling in extrusion of light alloys [Relazione in Atti di Convegno]
Santangelo, Paolo Emilio; Pelaccia, Riccardo; Rinaldi, Gabriele; Reggiani, Barbara; Orazi, Leonardo
abstract

Extrusion of light alloys is considered one of the most relevant processes in high-volume manufacturing. Production rate shall be kept as high as possible; however, the process bears limitations due to the operating conditions and mechanisms, which yield a large amount of heat generated by deformation energy and friction forces. Profile temperature likely reaches values close to 580 – 590 °C and the resulting thermal stress may reduce the tool life and lead to cracks and defects in the profile. Therefore, cooling of the zones where the higher temperatures occur is instrumental. Nitrogen has been recently brought at the forefront as a coolant, thanks to its low boiling point at atmospheric pressure. However, the design of cooling channels mostly relies on models that include either the liquid or the gas phase. The present work is focused on assessing the homogenous-flow approach as a method representative of the involved physics, also not being as computationally demanding as those simulating both phases. A Finite Element model was developed in a multiphysics environment, encompassing both the extrusion process and the nitrogen flow. The latter consisted of a homogeneous flow requiring dedicated formulation of thermophysical properties. Transient analyses were carried out with different models and the results were validated against an experimental dataset that stemmed from AA6063 billets extruded at variable speed in a reduced-scale industrial line. The ability to predict temperature measured at a location close to the billet was evaluated. The results from homogeneous flow modeling appear the most accurate, whereas modeling only the liquid phase leads to an overestimation of the cooling effect, as opposed to the underestimation associated with including the sole gas phase. Running time also proved as short as industry typically requires.

2023 - Experimental assessment and predictive model of the performance of Ti-based nanofluids [Articolo su rivista]
D'Adamo, Alessandro; Diana, Martino; Corda, Giuseppe; Cucurachi, Antonio; Cannio, Maria; Pellacani, Andrea; Romagnoli, Marcello; Stalio, Enrico; Santangelo, Paolo Emilio
abstract

The need for innovative propulsion technologies (e.g., fuel cells) in the mobility sector is posing a higher-than-ever burden on thermal management. When low operative temperature shall be ensured, dissipation of a significant amount of heat is requested, together with limited temperature variation of the coolant; mobile applications also yield limitations in terms of space available for cooling subsystems. Nanofluids have recently become one of the most promising solutions to replace conventional coolants. However, the prediction of their effectiveness in terms of heat-transfer enhancement and required pumping power still appears a challenge, being limited by the lack of a general methodology that assesses them simultaneously in various flow regimes. To this end, an experiment was developed to compare a conventional coolant (ethylene glycol/water) and a TiO2-based nanofluid (1% particle loading), focusing on heat transfer and pressure loss. The experimental dataset was used as an input for a physical model based on two independent figures of merit, aiming at an a priori evaluation of the potential simultaneous gain in heat transfer and parasitic power. The model showed conditions of combined gain specifically for the laminar flow regime, whereas turbulent flows proved inherently associated to higher pumping power; overall, criteria are presented to evaluate nanofluid performance as compared to that of conventional coolants. The model is generally applicable to the design of cooling systems and emphasizes laminar flow regime as promising in conjunction with the use of nanofluids, proposing indices for a quantitative a priori evaluation and leading to an advancement with respect to an a posteriori assessment of their performance.

2023 - Experimental assessment of the acoustic performance of nozzles designed for clean agent fire suppression [Articolo su rivista]
Strianese, Marco; Torricelli, Nicolo; Tarozzi, Luca; Santangelo, Paolo Emilio
abstract

Discharge through nozzles used in gas-based fire protection of data centers may generate noise that causes the performance of hard drives to decay considerably; silent nozzles are employed to limit this harmful effect. This work focuses on proposing an experimental methodology to assess the impact of sound emitted by gaseous jets by comparing various nozzles under several operating conditions, together with relating that impact to design parameters. A setup was developed and repeatability of the experiments was evaluated; standard and silent nozzles were tested regarding the discharge of inert gases and halocarbon compounds. The ability of silent nozzles to contain the emitted noise—generally below the 110 dB reference threshold—was proven effective; a relationship between Reynolds number and peak noise level is suggested to support the reported increase in noise maxima as released flow rate increases. Hard drives with lower speed were the most affected. Spectral analysis was conducted, with sound at the higher frequency range causing performance decay even if lower than the acknowledged threshold. Independence of emitted noise from the selected clean agent was also observed in terms of released volumetric flow rate, yet the denser the fluid, the lower the generated noise under the same released mass flow rate.

2022 - A Homogeneous Flow Model for nitrogen cooling in the aluminum-alloy extrusion process [Articolo su rivista]
Pelaccia, Riccardo; Santangelo, Paolo Emilio
abstract

Extrusion of aluminum alloys has become extensively employed as a process to manufacture a variety of products. However, heat generated by the high deformation energy and the high friction forces imposed during the process may cause defects in the extrudate, as well as reduce tool life. So, effective die cooling is key in achieving high product quality and production rate. Nitrogen has recently been identified as a promising coolant; however, current modeling does not take the presence of two phases into account, only including either the liquid or the gas phase within cooling channels, which often results in poorly designed cooling systems. The present research was aimed at exploring the homogenous flow approach as a simple, yet representative method to account for the liquid and the gas phase, as they both occur during the cooling subprocess. Ten AA6060 billets were extruded in an industrial production line, varying nitrogen flow rate and monitoring temperature trend at various locations of interest. A Finite Element model was then developed in a multiphysics environment, into which the simulation of both the extrusion process and the nitrogen flow were integrated, with the latter being represented as a homogeneous flow. Validation was performed against the experimental dataset through steady-state and transient analysis. This work proved the homogeneous-flow approach remarkably successful in capturing the involved physics and assessing the provided cooling effect quantitatively.

2022 - An experimental approach to evaluate drying kinetics and foam formation in inks for inkjet printing of fuel-cell layers [Articolo su rivista]
Santangelo, Paolo Emilio; Romagnoli, Marcello; Puglia, Marco
abstract

Inkjet printing is a deposition technique that has remarkably evolved over the last two decades, becoming widely employed for various applications. Notably, it has proven very promising for catalyst and ionomer layer deposition in assembling CCM (Catalyst Coated Membranes) of PEMFC (Polymer Electrolyte Membrane Fuel Cells). However, fast drying of the processed inks at the outlet often causes nozzle clogging and foam formation within the supply circuit often yields poor release: these are the main challenges in applying inkjet printing on a large scale. So, an experimental approach for the evaluation of drying kinetics and foam formation in inks typically employed in fuel-cell manufacturing is presented. It allows to evaluate ink printability, compare different inks quantitatively and assess the performance of commonly used additives. Evaluation of drying kinetics is based on releasing ink droplets onto a support, then recording mass, ambient temperature and relative humidity. Foam formation is evaluated by filling a syringe with a known amount of ink, then injecting air at a set flow rate into the sampling volume: foam may be ultimately generated and its amount can be measured. Those relatively simple approaches were applied to various inks; validation was conducted by statistical analysis and by comparison with physical relationships and datasets available in the open literature.

2022 - Full-scale experiments of water-mist systems for control and suppression of sauna fires [Articolo su rivista]
Santangelo, Paolo Emilio; Tarozzi, Luca; Tartarini, Paolo
abstract

Sauna is a common fixture in many facilities; a specific fire-protection system is typically designed and installed for this application, as short circuits or direct contact with incandescent materials may result in a fire. Water mist has been recently considered as a promising option for this purpose; so, assessing its control and suppression capability in a sauna configuration has become of paramount importance for designers and engineers. To this end, an unprecedented real-scale test rig was built and instrumented with thermocouples and a hot-plate thermometer towards the evaluation of water-mist performance against various fire scenarios and, ultimately, to provide guidelines to designers. Timber benches were employed as target materials, while the fire was initiated in a wood crib. Design parameters, such as initial room temperature, location of the ignition source, nozzle-to-wall distance, and air gap between benches and wall, were varied, also including natural ventilation in a dedicated experiment. The system proved successful in controlling and containing the fire: bench damage ratio—selected as a quantitative parameter to assess water-mist performance—was consistently lower than 5%. However, extinction was not always achieved, especially under the most challenging configuration in terms of ventilation, initial room temperature, and nozzle-to-wall distance.

2022 - Multilayer additive manufacturing of catalyst-coated membranes for polymer electrolyte membrane fuel cells by inkjet printing [Articolo su rivista]
Willert, Andreas; Tabary, Farzin Z.; Zubkova, Tatiana; Santangelo, Paolo Emilio; Romagnoli, Marcello; Baumann, Reinhard R.
abstract

Inkjet printing is a versatile, contactless and accurate material deposition technology. The present work is focused on developing innovative strategies for inkjet printing of Catalyst-Coated Membranes (CCM) by performing Additive Manufacturing (AM) applied to Polymer Electrolyte Membrane Fuel Cells (PEMFC), without resorting to intermediate substrates. Three different approaches for AM are presented and discussed: a) inkjet-printing of the membrane ionomer layer and the top catalyst layer; b) inkjet-printing of both catalyst layers onto a membrane; c) inkjet-printing of the ionomer layer as well as the catalyst layers onto the reinforcement layer of the membrane. The produced catalyst and membrane layers were characterized and proved uniform in terms of catalyst loading (0.2 – 0.4 and 0.08 mgPt cm-2 for cathode and anode, respectively), ionomer distribution and thickness homogeneity (4 μm for catalyst layers). The fully inkjet-printed CCM outperformed conventionally made assemblies in electrochemical-performance testing, even reaching 15% higher power density.

2021 - Smart catalyst deposition by 3D printing for Polymer Electrolyte Membrane Fuel Cell manufacturing [Articolo su rivista]
Cannio, Maria; Righi, Stefania; Santangelo, Paolo Emilio; Romagnoli, Marcello; Pedicini, Rolando; Carbone, Alessandra; Gatto, Irene
abstract

Polymer Electrolyte Membrane Fuel Cells (PEMFC) are arguably the most employed fuel-cell types in various industry sectors, as they operate at low temperature and exhibit short start-up time and high durability. PEMFC manufacturing is currently transitioning from low-volume to mass production. Within this effort, efficient catalyst deposition to produce MEA (Membrane Electrode Assembly) electrodes has become instrumental, since very expensive raw materials are involved. This work focuses on an Additive Manufacturing (AM) technique e a modified 3D printing approach e used to release catalytic inks onto PEMFC electrodes. Some catalyst-free suspensions were designed to resemble a catalytic ink and characterized to assess their printability by microextrusion. Mixtures of distilled water, ethanol and graphite were prepared and tested. Granulometric and rheometric analyses were conducted to optimize the composition towards low viscosity values and short drying time. Repeatability of the released amount and its homogeneousness onto the target surface were evaluated. The most suitable ink formulation was loaded with platinum, a perfluorosulfonic ionomer, a pore former (NH4CO3) and deposited onto Gas Diffusion Layers (GDL). Scanning Electron Microscopy (SEM) measurements were performed on the 3D-printed electrodes to characterize it. Preliminary electrochemical fuel-cell tests were carried out towards a comparison with conventional electrodes: the proposed deposition technique appears able to produce electrodes that align with state-of-the-art performance level.

2019 - Evaluation of heat-wrap thermal transient behavior: The development of an experimental test procedure [Relazione in Atti di Convegno]
Santangelo, Paolo Emilio; Santunione, Giulia; Muscio, Alberto
abstract

Heat wraps represent the most used thermotherapy methods over the last 2 decades as a self-administered practice for pain relief. A deep knowledge regarding their performance has become a priority within healthcare industry. However, the majority of the available studies have been focused on in vivo clinical performance, whereas a standardized, quantitative approach to evaluate and compare the various heat-wrap types against each other is lacking. An experimental methodology is proposed to carry out a comparative assessment between heat wraps in terms of their transient thermal behavior. A simple setup was developed to measure wrap/substrate interface temperature trend. The approach was validated by a preliminary infrared-thermography assessment and statistical analysis on the extensive dataset acquired on commercial heat-wrap types for low-back and neck pain relief. The heat-release trend was found to be qualitatively similar over all the investigated types, consisting of rapid growth, stationary phase, decay and end of the reactions. A set of parameters is also proposed to summarize heat-wrap thermal performance.

2019 - Experimental methodology for quantitative assessment of heat-wrap thermal transient behavior [Articolo su rivista]
Santangelo, Paolo Emilio; Santunione, Giulia; Muscio, Alberto
abstract

Among the numerous thermotherapy methods, heat wraps have been largely used over the last 2 decades as a self-administered practice for pain relief. Therefore, understanding their performance has become instrumental within the healthcare industry. However, the majority of the available studies have been focused on in vivo clinical performance, whereas a standardized, quantitative approach to evaluate and compare the various heat-wrap types against each other is lacking. An experimental methodology is proposed to carry out a comparative assessment between heat wraps in terms of their transient thermal behavior. A simple setup was developed to measure wrap/substrate interface temperature trend. The approach was validated by a preliminary infrared-thermography assessment and statistical analysis on the extensive dataset acquired on commercial heat-wrap types for low-back and neck pain relief. The heat-release trend was found to be qualitatively similar over all the investigated types, consisting of rapid growth, stationary phase, decay and end of the reactions. A set of parameters is also proposed to sum-marize heat-wrap thermal performance.

2019 - MAMA-MEA, Mass Manufacture of MEAs Using High Speed Deposition Processes [Relazione in Atti di Convegno]
Romagnoli, Marcello; Santangelo, Paolo Emilio
abstract

The scope of MAMA-MEA is to develop an innovative additive-layer deposition process that integrates all the main CCM (Catalyst Coated Membrane) components within a single, continuous roll-to-roll production line. This project is focused on PEMFC Polymer Electrolyte Membrane Fuel Cell) industry. Its mission is to foster an increase of the manufacturing rate up to 10 times faster than that currently achieved by state-ofthe-art processes. The current manufacturing methods will not be able to meet CCM demand over the next 10 years, therefore, new strategies needs be sought, explored and translated into high volume production lines to augment the capacity and follow the expected trend. The whole effort also has the potential to improve material utilisation and manufacturing costs. Preliminary one-off prototypes have already established the feasibility of the proposed approach and patent applications have been filed. The engineering design of an ALM sealed CCM production line will be provided.

2019 - Review of catalyst-deposition techniques for PEMFC electrodes [Articolo su rivista]
Santangelo, Paolo Emilio; Cannio, Maria; Romagnoli, Marcello
abstract

Catalyst deposition has been a significant part of fuel-cell manufacturing since their entry into mass-production industry, especially to limit the inevitable use of critical raw materials. This review focuses on a variety of techniques that may be applied towards a controlled deposition onto PEMFC substrates. The current manufacturing process consists of depositing inks onto decal-transfer carrier films, then bound to the membrane by heat and pressure. Among the conventional methods for ink deposition, gravure printing and screen printing appear the most promising. The former consists of engraving the desired image areas into the surface of a cylinder; the ink lies ultimately within engraved cells and is transferred from those cells to the substrate. In screen printing, the ink is forced through a fine fabric screen and flows through the open meshes, according to the desired pattern. Additive layer manufacturing and inkjet printing are also considered as prominent alternatives, thanks to their higher ink-deposition control onto the substrate, mainly through the drop-on-demand approach. The need for achieving higher flexibility and quality in MEA production seems to favor inkjet printing and additive layer manufacturing, able to lead to a significantly higher catalyst-layer homogeneousness. However, they require assessment of ink rheological properties and formulation.

2019 - Smart catalyst deposition by 3D printing for low temperature fuel cells [Abstract in Atti di Convegno]
Cannio, Maria; Santangelo, Paolo Emilio; Romagnoli, Marcello; Pedicini, Rolando; Gatto, Irene
abstract

Polymer Electrolyte Membrane Fuel Cells (PEMFC) are arguably the most robust and integrated into various industry sectors among fuel cells, as they operate at low temperature and exhibit short start-up time. Currently, PEMFC manufacturing is transitioning from low-volume to mass production. However, the major hindrance against their massive use consists of high materials costs, low power density and relatively short lifetime. Notably, the need for employing platinum as a catalyst promotes exploring more convenient and effective manufacturing routes. The present work focuses on applying a microextrusion-based 3D printing system to deposit catalyst layers onto the Membrane-Electrode Assembly (MEA). A commercial 3D printer was modified to support the MEA substrate; furthermore, a peristaltic pump was inserted to supply the microextrusion printhead with the catalyst-endowed ink, finally released by a syringe. The main objectives of this work were to provide optimized compositions of catalyst inks suitable for MEA and (Gas Diffusion Layer) GDL preparation, and to assess the effectiveness of the microextrusion-based 3D printing technique in yielding homogeneous coatings. The ink was a mixture of distilled water, ethanol and graphite. Granulometric and rheometric analyses were carried out to characterize inks in a quest for low viscosity and short drying time. Repeatability of released flow rate and ink homogeneity onto the GDL target surface were also evaluated by statistical analysis. The final assessment of the coated substrates was performed by measuring the characteristic polarization curve. The results suggest that microextrusion-based 3D printing can be considered as a promising technology for fuel-cell manufacturing.

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 - 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 - Review of catalyst-deposition techniques for PEMFC electrodes [Relazione in Atti di Convegno]
Santangelo, Paolo Emilio; Cannio, Maria; Romagnoli, Marcello
abstract

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 - Infrared thermography as a Non-destructive Testing solution for thermal spray metal coatings [Articolo su rivista]
Santangelo, Paolo Emilio; Allesina, Giulio; Bolelli, Giovanni; Lusvarghi, Luca; Matikainen, Ville; Vuoristo, Petri
abstract

In this work, an infrared (IR) thermographic procedure was evaluated as a non-destructive testing tool to detect damage in thermal spray metallic coatings. As model systems, polished HVOF- and HVAF-sprayed Fe-based layers deposited onto steel plates were employed. Damage by external-object impingement was simulated through a cyclic impact-test apparatus, which induced circumferential and radial cracks across all model systems, and interface cracks of different sizes in distinct samples. Damaged and undamaged plates were bulk-heated to above 100 °C using an IR lamp; their free-convection cooling was then recorded by an IR thermocamera. The intentionally induced defects were hardly detectable in IR thermograms, due to IR reflection and artificial ‘‘hot’’ spots induced by residuals of transfer material from the impacting counterbody. As a micrometer-thin layer of black paint was applied, surface emissivity got homogenized and any artifacts were effectively suppressed, so that failed coating areas clearly showed up as ‘‘cold spots.’’ This effect was more apparent when large interface cracks occurred. Finite-element modeling proved the physical significance of the IR-thermography approach, showing that failed coating areas are cooled by surrounding air faster than they are heated by conduction from the hot substrate, which is due to the insulating effect of cracks.

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 - 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.

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.

2014 - Analyzing fire-induced dispersion and detector response in complex enclosures using salt-water modeling [Articolo su rivista]
Jankiewicz, Sean P.; Siang, Chan C.; Yao, Xiaobo; Santangelo, Paolo Emilio; Marshall, André W.; Roby, Richard J.
abstract

The current investigation examines suitability of the hydraulic analog for analysis of fire-induced dispersion within a complex enclosure. This analog has been implemented using salt-water modeling and planar laser induced fluorescence (PLIF) diagnostics providing quantitative visualization of simulated fire-induced flows. The non-intrusive PLIF diagnostics are used to temporally and spatially characterize dispersion from a buoyant source within a 1/7th scale room-corridor-room enclosure. This configuration is geometrically similar to a full-scale fire test facility, where local fire conditions were characterized near five ionization type smoke detectors placed throughout the enclosure. The full-scale fire and salt-water model results were scaled according to the dimensionless fundamental equations that govern source dispersion. An evaluation of the local conditions and dispersive event times for both the systems was used to explore the ability of the hydraulic analog to predict smoke detector response times. The dispersive event (front arrival) times predicted by the salt-water model, which represents a necessary event for detector activation, were in excellent agreement with the fire test data. A methodology using these front arrival times along with local conditions at the detector location is introduced in this paper. However, the complex nature of detector response and fidelity limitations of the analog make precise predictions of detector response time challenging. The predicted dimensionless response times were within 25% for all detector locations, with the exception of the first-room ceiling detector location. For this latter, a shorter dimensionless response time by less than 40% of that in the actual fire was predicted. Â© 2014 Elsevier Ltd.

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.

2014 - Suppression effectiveness of water-mist sprays on accelerated wood-crib fires [Articolo su rivista]
Santangelo, Paolo Emilio; Jacobs, Bryson C.; Ren, Ning; Sheffel, Joshua A.; Corn, May L.; Marshall, André W.
abstract

An experimental analysis was conducted to quantify the water-mist discharge characteristics required to suppress wood-crib fires. The overall aim of this research was to investigate the effectiveness of these innovative systems in a canonical fire scenario. To this end, an experimental suppression facility was constructed including commercially available water mist nozzles, thermocouples for measuring the thermal transient in and around the wood cribs and a load cell for measuring the mass loss rate and the final wood crib damage. 510Ã510Ã380 mm wood cribs were used as the fuel source in all the experiments. The injection pressure and orifice diameter of the water-mist nozzles were varied in the experiments to modify the applied water flux and the initial spray momentum. These quantities were identified to be the governing parameters for suppression performance. They were characterized for all experiments along with the drop-size and velocity distributions. Critical values were determined for these quantities from first order kinematic and thermal analysis based on spray and fire source characteristics. The experimental results demonstrated critical suppression behavior consistent with this first order analysis.

2012 - Evaluation of flow direction methods against field observations of overland flow dispersion [Abstract in Rivista]
Orlandini, Stefano; Moretti, Giovanni; Corticelli, Mauro Alessandro; Santangelo, Paolo Emilio; Capra, Alessandro; Rivola, Riccardo; D. Albertson., John
abstract

Despite the broad effort made in grid-based distributed catchment modeling to account for planar overland flow dispersion, actual dispersion experienced by overland flow along a natural slope has not been measured so far, and the ability of terrain analysis methods to reproduce this dispersion has not been evaluated. In the present study, the D8, D8-LTD, D$infty$-LTD, D$infty$, MD$infty$, and MD8 flow direction methods are evaluated against field observations of overland flow dispersion obtained from novel experimental methods. Thin flows of cold (2--10$^circ$C) water were released at selected points on a warmer (15--30$^circ$C) slope and individual overland flow patterns originating from each of these points were observed using a terrestrial laser scanner and a thermal imaging camera. Prior to each experimental water release, a ScanStation C10 terrestrial laser scanner by Leica Geosystems was used to acquire a point cloud having average density of 25~points/cm$^2$. This point cloud was used to generate alternative grid-based digital elevation models having resolution $h$ ranging from 1~cm to 2~m. During the experiments, an Avio Advanced Thermo TVS-500EX camera by Nippon Avionics was used to monitor land surface temperature with resolution better than $0.05^circ$C. The overland flow patterns were also found to be discernible in terrestrial laser scanner reflectance signal acquired immediately following the flow experiments. Overland flow patterns were determined by considering contrasted temperature and reflectance of the dry and wetted land surface portions. Predicted propagation patterns and observed flow patterns were compared by considering the fractions of flow released at the point source that propagates through the grid cells. Predictions of these quantities were directly provided by flow direction methods and by related flow accumulation algorithms. Suitable data for the comparison were derived from observed overland flow patterns by assuming a uniform distribution of flow along each cross section. Planar overland flow dispersion is found to play an important role in the region lying immediately downslope of the point source, but attenuates rapidly as flow propagates downslope displaying a nearly constant width of about 50~cm. In contrast, existing dispersive flow direction methods are found to provide a continued dispersion with distance downslope. Predicted propagation patterns, for all methods considered here, depend critically on $h$. All methods are found to be poorly sensitive in extremely fine grids ($h leq 2$~cm), and to be poorly specific in coarse grids ($h = 2$~m). Satisfactory results are, however, obtained when $h$ approaches the average flow width, with the best performances in terms of Pearson correlation coefficient displayed by the MD8 method in the finest grids ($5~{ m cm} leq h leq 20~{ m cm}$), and by the MD$infty$, D$infty$, and D$infty$-LTD methods in the coarsest grids ($20~{ m cm} < h leq 1~{ m m}$). The results obtained in this study suggest further testing of terrain analysis methods with longer flow patterns and coarser grids. Scale issues affecting the relation between land surface microtopography, dispersion, and size of grid cells involved need then to be addressed to provide a hydrologic model of flow partitioning along the slope directions identified by terrain analysis methods.

2012 - Evaluation of flow direction methods against field observations of overland flow dispersion [Articolo su rivista]
Orlandini, Stefano; Moretti, Giovanni; Corticelli, Mauro Alessandro; Santangelo, Paolo Emilio; Capra, Alessandro; Rivola, Riccardo; Albertson, John D.
abstract

The D8, D8-LTD, D∞-LTD, D∞, MD∞, and MD8 flow direction methods are evaluated against field observations of overland flow dispersion obtained from novel experimental methods. Thin flows of cold water were released at selected points on a warmer slope and individual overland flow patterns originating from each of these points were observed using a terrestrial laser scanner and a thermal imaging camera. Land microtopography was determined by using laser returns from the dry land surface, whereas overland flow patterns were determined by using either laser returns or infrared emissions from the wetted portions of the land surface. Planar overland flow dispersion is found to play an important role in the region laying immediately downslope of the point source, but attenuates rapidly as flow propagates downslope. In contrast, existing dispersive flow direction methods are found to provide a continued dispersion with distance downslope. Predicted propagation patterns, for all methods considered here, depend critically on the size h of grid cells involved. All methods are found to be poorly sensitive in extremely fine grids (h ≤ 2 cm), and to be poorly specific in coarse grids (h = 2 m). Satisfactory results are, however, obtained in grids having resolutions h that approach the average flow width (50 cm), with the best performances displayed by the MD8 method in the finest grids (5 ≤ h ≤ 20 cm), and by the MD∞, D∞, and D∞-LTD methods in the coarsest grids (20 cm < h ≤ 1 m).

2012 - Evaluation of flow direction methods against field observations of overland flow dispersion [Relazione in Atti di Convegno]
Orlandini, Stefano; Moretti, Giovanni; Corticelli, Mauro Alessandro; Santangelo, Paolo Emilio; Capra, Alessandro; Rivola, Riccardo; Albertson, John D.
abstract

The D8, D8-LTD, D∞-LTD, D∞, MD∞, and MD8 flow direction methods are evaluated against field observations of overland flow dispersion obtained from novel experimental methods. Thin flows of cold water were released at selected points on a warmer slope and individual overland flow patterns originating from each of these points were observed using a terrestrial laser scanner and a thermal imaging camera. Land microtopography was determined by using laser returns from the dry land surface, whereas overland flow patterns were determined by using either laser returns or infrared emissions from the wetted portions of the land surface. Planar overland flow dispersion is found to play an important role in the region lying immediately downslope of the point source, but attenuates rapidly as flow propagates downslope. In contrast, existing dispersive flow direction methods are found to provide a continued dispersion with distance downslope. Predicted propagation patterns, for all methods considered here, depend critically on the size h of grid cells involved. All methods are found to be poorly sensitive in extremely fine grids (h ≤ 2 cm), and to be poorly specific in coarse grids (h = 2 m). Satisfactory results are, however, obtained in grids having resolutions h that approach the average flow width (50 cm), with the best performances displayed by the MD8 method in the finest grids (5 cm ≤ h ≤ 20 cm), and by the MD∞, D∞, and D∞-LTD methods in the coarsest grids (20 cm < h ≤ 1 m).

2012 - Experiments and modeling of discharge characteristics in water-mist sprays generated by pressure-swirl atomizers [Articolo su rivista]
Santangelo, Paolo Emilio
abstract

Pressure-swirl atomizers are often employed to generate a water-mist spray, typically employed in fire suppression. In the present study, an experimental characterization of dispersion (velocity and cone angle) and atomization (drop-size axial evolution) was carried out following a previously developed methodology, with specific reference to the initial region of the spray. Laser-based techniques were used to quantitatively evaluate the considered phenomena: velocity field was reconstructed through a Particle Image Velocimetry analysis; drop-size distribution was measured by a Malvern Spraytec device, highlighting secondary atomization and subsequent coalescence along the spray axis. Moreover, a comprehensive set of relations was validated as predictive of the involved parameters, following an inviscid-fluid approach. The proposed model pertains to early studies on pressure-swirl atomizers and primarily yields to determine both initial velocity and cone angle. The spray thickness is also predicted and a classic correlation for Sauter Mean Diameter is shown to provide good agreement with experimental results. The analysis was carried out at the operative pressure of 80 bar; two injectors were employed featuring different orifice diameters and flow numbers, as a sort of parametric approach to this spray typology. Â© Science Press and Institute of Engineering Thermophysics, CAS and Springer-Verlag Berlin Heidelberg 2012.

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 - Suppression effectiveness of water sprays on accelerated wood-crib fires [Relazione in Atti di Convegno]
Santangelo, Paolo Emilio; Jacobs, Bryson C.; Ren, Ning; Sheffel, Joshua A.; Corn, May L.; Marshall, André W.
abstract

Solid-fire extinguishment by water sprays has received remarkable attention over the decades. Though several approaches have been taken to understand the important physical phenomena, empirical correlations remain very common in discussions of these fires. Historically, wood-cribs have offered an important means by which to study the extinguishment of combustible solids, as their simple and well-defined structure lends a degree of repeatability to experimental investigations. Therefore, several classical experiments in this area focus on wood-crib fuel packages [1-3]. The primary objective of this mainly experimental study is to determine the relationship between the water flux applied to a burning wood crib and the total damage sustained by the crib, as assessed by the crib’s mass loss. A thermodynamic discussion of the potential cooling mechanisms also provides physical insight into the suppression results. As an additional feature of the present work, an experimental characterization of the water mist spray was performed in terms of flux and drop-size distribution, following previous spray studies [4]. Moreover, additional parameters were investigated to better understand the wood-crib fire dynamics (e.g., air entrainment at the lateral surface and heat release rate).

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 - 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 Â© 2011 by ASME.

2011 - Flammability of solid materials: An experimental calorimetric approach [Relazione in Atti di Convegno]
Santangelo, Paolo Emilio; Ryder, Noah L.; Marshall, André W.; Schemel, Christopher F.
abstract

Flammability properties of solid materials are necessary to be a known parameter for many purposes: among them, forensic investigations of fire and explosion events, fire risk or hazard analysis, design and development of combustion-based systems. However, despite the large quantity of data in the literature, the flammability properties of many materials still appear not to be available or show a degree of uncertainty associated with them, which makes their value limited. The present work is aimed at proposing a calorimetric-based approach to determine some flammability and thermophysical properties of solids, with specific regard to time-to-ignition as a function of the imposed heat flux. Plastic materials have been here chosen as test cases, even though this approach has a general applicability. The two mentioned parameters have been analyzed to provide a quantitative estimation of the critical heat flux (minimum heat flux resulting in ignition). A cone calorimeter has been employed to conduct the experiments: the facility complies with standard ASTM E 1354; the related uncertainty and validity range has been evaluated through an appropriate error analysis. Finally, thermal inertia has been thereby calculated for the considered materials through a simple thermodynamic model, which is based upon critical heat flux and energy conservation. Copyright Â© 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.

2010 - Characterization of high-pressure water-mist sprays: Experimental analysis of droplet size and dispersion [Articolo su rivista]
Santangelo, Paolo Emilio
abstract

Popularity of water mist is increasing for a variety of applications within the broad areas of fire suppression and surface cooling. The present study has been focused on characterizing the solid-cone water-mist spray produced by a typical atomizer at high operative pressure (in the range 60-80. bar). To this end, an experimental campaign has been conducted, mainly employing optical techniques: drop-size and flux distribution, initial velocity and cone angle have been investigated to provide a quantitative description of atomization and dispersion. Most notably, a laser-diffraction-based instrument (Malvern Spraytec) has been used to evaluate drop size, while velocity field and spray-cone angle have been studied by Particle Image Velocimetry (PIV) technique. Appropriate measurement methodologies have been developed to the purpose. Moreover, a theoretical discussion based on inviscid-fluid assumption is presented and some relations have been evaluated as predictive of the considered parameters. Â© 2010 Elsevier Inc.

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 FluentÂ® 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. Â© 2010 by ASME.

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.

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 - 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 - 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 - 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 - 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.

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 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 - 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.

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 - 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.

Università degli studi di Modena e Reggio Emilia

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