Mauro Alessandro CORTICELLI - personale UniMoRe

Nuova ricerca

Mauro Alessandro CORTICELLI

Professore Ordinario
Dipartimento di Ingegneria "Enzo Ferrari"

Pubblicazioni

2020 - Compressible Fanno flows in micro-channels: An enhanced quasi-2D numerical model for turbulent flows [Articolo su rivista]
Cavazzuti, M.; Corticelli, M. A.; Karayiannis, T. G.
abstract

Fanno theory provides an analytical model for one-dimensional confined viscous compressible flows. The model holds under the assumptions of adiabatic flow and constant cross-section channel. From theory, the differential of every flow-related quantity is expressed as a function of Mach number and friction factor. One-dimensional flow numerical models can be derived by discretizing Fanno equations. However, theory does not assess how to evaluate friction, while the model works properly only if friction is estimated correctly. Compressibility and turbulence act by deforming the velocity profile making it flatter. Assuming the friction factor function of the Reynolds number alone, in line with incompressible flow theory, is thus not correct. Better correlations should include the Mach number to address compressibility effects. Here, the impact of turbulence and compressibility on the velocity profiles in a micro-channel is analysed by means of CFD simulations. Friction factor correlations are deduced for turbulent micro-flows. The impact of the velocity profile on other quantities, such as dynamic pressure and bulk temperature, needed for the numerical model operation, is also evaluated. Additional correlations for these quantities overcome the instrinsic limits of the one-dimensional model, necessarily unaware of local velocity profiles, in a quasi-2D fashion significantly improving its predicting capabilities.

2019 - Compressible Fanno flows in micro-channels: An enhanced quasi-2D numerical model for laminar flows [Articolo su rivista]
Cavazzuti, Marco; Corticelli, Mauro A.; Karayiannis, Tassos G.
abstract

Micro-scale fluid systems are becoming common in many applications ranging from electronic cooling to refrigeration systems and more. One-dimensional numerical models represent a simple and fast tool for the design of such devices, yet they struggle to accurately predict the flow characteristics in compressible micro-flows. Under the adiabatic assumption, the elegant theory developed by Fanno allows models for the viscous compressible flow in constant cross-section channels to be easily built. Although reasonably accurate, these models suffer from drawbacks inherent to their being one-dimensional, as such they cannot take into account the local profiles of quantities like the velocity and the temperature. In cascade, this results into incorrect evaluations of other dependent quantities, such as the dynamic pressure and the fluid thermophysical properties. The mismatch turns large when the fluid compressibility becomes important. As the Mach number grows, the velocity profile changes, and so the friction factor, even though a reliable model for predicting this change is still missing. In fact, a constant friction factor throughout the channel is generally assumed, following the incompressible flow theory. Here, a set of correlations is proposed improving the 1D theory accuracy by taking into account the effects of the non-uniform velocity and temperature profiles in a quasi-2D fashion. A detailed analysis of the velocity profiles at different Mach numbers coming from a large set of CFD simulations results in a model for assessing the impact of compressibility on friction and other quantities. The numerical model proposed, being able to properly account for the compressibility effects, offers an improved tool for the design of micro-scale fluid systems. Extending the analysis to include heat transfer is not difficult as the effect of heat flux will be analogous to the effect of pressure drop due to friction.

2019 - Compressible flows in micro-channels: an enhanced quasi-2D Fanno-based numerical model [Relazione in Atti di Convegno]
Cavazzuti, Marco; Corticelli, Mauro A.; Karayiannis, Tassos G.
abstract

Fanno theory provides an analytical model for the prediction of confined viscous compressible flows under the hypotheses of constant cross-section channel and adiabatic flow. From theory, differentials of flow characteristic quantities can be expressed in function of Mach number and friction factor. Yet, the theory does not assess how to evaluate friction, whereas classical formulas for friction prediction in channels are derived under the hypothesis of incompressible flow and are no longer valid in case of compressible flows. Compressibility deforms the velocity profiles in the channel by making them more flat. As a consequence friction is increased compared to the incompressible case. At the same time, the change in the velocity profiles affects the average dynamic pressure and the bulk temperature along the channel. Correlations, function of Mach and Reynolds numbers, are required for quantifying these changes and improve the prediction of the Fanno model. In the present paper, the impact of compressibility on laminar and turbulent flows in micro-channels is assessed on the basis of a series of CFD simulations, and correlations are presented for friction, average dynamic pressure, and bulk temperature. The correlations are proven to enhance the accuracy of the Fanno model predictions.

2019 - Velocity profile development and friction in compressible micro-flows [Relazione in Atti di Convegno]
Cavazzuti, Marco; Corticelli, Mauro A.; Karayiannis, Tassos G.
abstract

rom Poiseuille theory, it is known that incompressible laminar fully-developed flow of a Newtonian fluid in a constant cross-section channel is characterised by steady parabolic velocity profiles after a fully-developed flow condition is attained. In turbulent fully-developed flow the velocity profiles are non-parabolic and become more flat for higher Reynolds numbers. When the incompressible hypothesis does not hold, as in the case of high velocity ideal gas flow, the velocity profile becomes flatter, as if more turbulent, due to the superposition of compressibility and turbulence effects, if applicable. This is typical in micro-channel flows, where pressure gradients are high and the gas is rapidly accelerating, eventually up to the sound velocity. As the flow accelerates the effects of compressibility grow stronger and the velocity profile keeps changing shape. The radial velocity component does not zero as in fully-developed flow but reverses after the entrance effects have damped out and grows with the Mach number. A net mass transfer toward the walls is thus generated making the velocity profile more flat. This affects the friction factor which is no longer constant, being proportional to the normal-to-wall velocity gradient, and needs to be evaluated. In the present work, the compressible friction factor is numerically investigated and correlations are proposed based on the velocity profile shape evolution as a function of the Mach number. This, together with other considerations on the velocity profile shape change, is shown to enhance the predictive capability of the Fanno theory for compressible flows.

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.

2017 - An algorithm for solving steady-state heat conduction in arbitrarily complex composite planar walls with temperature-dependent thermal conductivities [Articolo su rivista]
Cavazzuti, Marco; Corticelli, Mauro Alessandro
abstract

An algorithm for solving steady-state heat conduction problems in arbitrarily complex composite walls is presented. Per se, steady-state heat conduction across a wall can easily be solved by hand. Yet, in practical applications the wall structure is often complex enough to deter such an approach if a finer yet simple analysis of the thermal bridges is of interest. Moreover, if high-temperature applications are involved, the additional complexity of including time-dependent thermal conductivity must be considered. Thus, a general methodology for solving arbitrary topology walls, involving any kind of thermal resistances in series and in parallel is discussed. While such a problem is formally simple to solve for a given wall following the theory, its algorithmic generalization is not. A method is provided, involving a program written in python language. The focus of the work is mainly on the algorithmic point of view: a simple way for the assessment of the wall topology and for the resolution of the heat conduction problem originating is sought. Temperature-dependent thermal conductivity of the materials is addressed, resulting in the need of evaluating the heat fluxes and the average temperature at each thermal resistance.

2017 - Application of Recurrence Analysis to the period doubling cascade of a confined buoyant flow [Relazione in Atti di Convegno]
Angeli, Diego; Corticelli, Mauro Alessandro; Fichera, A.; Pagano, A.
abstract

Recurrence Analysis (RA) is a promising and flexible tool to identify the behaviour of nonlinear dynamical systems. The potentialities of such a technique are explored in the present work, for the study of transitions to chaos of buoyant flow in enclosures. The case of a hot cylindrical source centred in a square enclosure, is considered here, for which an extensive database of results has been collected in recent years. For a specific value of the system aspect ratio, a sequence of period doublings has been identified, leading to the onset of chaos. RA is applied here to analyse the different flow regimes along the route to chaos. The qualitative visual identification of patterns and the statistics given by the quantitative analysis suggest that this kind of tool is well suited to the study of transitional flows in thermo-fluid dynamics.

2017 - Convective heat transfer of turbulent decaying swirled flows in concentric annular pipes [Articolo su rivista]
Cavazzuti, Marco; Corticelli, Mauro Alessandro
abstract

The heat transfer characteristics of turbulent decaying swirled flows in concentric annular pipes is investigated numerically by means of CFD simulations using the OpenFOAM package. The simulations are performed for different Reynolds numbers and swirl angles at the duct inlet. By including cases with large temperature differences between the fluid and the wall, also the effects of radial temperature gradients on the velocity distribution are accounted for. A novel correlation, holding locally, is proposed and is presented in a form similar to the classical Sieder-Tate correlation, including an additional term to address the influence of the swirled flow. In a similar fashion, a correlation for the friction factor is given in the form of the Petukhov formula, yet with an additional swirl-related term. Also a formula assessing the swirl decay rate is presented. This allows global correlations to be extracted by solving the local ones over the pipe length in a system and integrating.

2017 - Features of a blue-sky transition in an autonomous convective flow [Articolo su rivista]
Angeli, D.; Corticelli, M. A.; Fichera, A.; Pagano, A.
abstract

The nonlinear dynamics of a buoyant air flow in the gap formed by a horizontal cylindrical heat source and a concentric isothermally cooled square enclosure have been recently studied, in the limits of a two-dimensional approximation, for different values of the system aspect ratio, defined as the ratio between the cavity side length and the minimum gap width. Accurate analyses have revealed that, for low values of the aspect ratio, the dominant pattern is the swaying motion of a buoyant plume, which undergoes a period-doubling cascade for increasing values of the Rayleigh number. On the other hand, a substantially different behaviour has been preliminarily observed for higher values of the aspect ratio, since, in a thinner gap, the flow exhibits Rayleigh-BÃ©nard-like cellular patterns above the cylinder. The aim of this communication is to describe the peculiar route to chaos which has been detected for this second type of geometry. The scenario consists in the progressive winding of a periodic limit cycle on an attractor whose topology resembles that of a French horn, which is a typical signature of the codimension-2 Shilnikov bifurcation from periodic dynamics to chaos. A similar feature, known as the blue-sky catastrophe, has never been reported so far for confined convection of pure fluids.

2017 - Notes and experiments on the statics of capillary columns [Relazione in Atti di Convegno]
Barozzi, Giovanni Sebastiano; Corticelli, Mauro Alessandro; Angeli, Diego; Salerno, Elisabetta
abstract

Experimental results are summarized, concerned with the statics of liquid columns in capillary tubes under non-standard conditions. Three configurations are considered: 1. inclined capillary tubes; 2. capillary effect in the horizontal branch of an L-shaped tube; 3. capillary columns in a vertical tube. The effect of inclination on capillary rise (1.) had already been explored in [1] using water in glass-tubes, and it was found that the vertical rise progressively reduces for increasing the tube inclination. This behavior is now confirmed for n-Hexadecane (C16H34). For L-shaped capillaries (2.), the length of the horizontal branch of the tube occupied by the liquid is detected, as a function of the elevation of the branch itself over the feeding pool. The statics of suspended liquid columns (3.) is investigated for two configurations, namely: i. freely suspended columns, and, ii. edge-ending columns. In the latter case, the evaporation transient is also tracked. Even if the experimental basis is limited, the results are sufficient to highlight some of the peculiar features of the statics of capillary columns under the above conditions. In particular, it is shown that the contact angle hysteresis plays a fundamental role in all the cases considered.

2017 - Numerical modelling of Fanno flows in micro channels: a quasi-static application to air vents for plastic moulding [Articolo su rivista]
Cavazzuti, Marco; Corticelli, Mauro Alessandro
abstract

The flow in micro air vents, as those used in the plastic moulding industry, can be assimilated to a Fanno flow. Even though Fanno theory is well-established, its outcome strongly depends on the correct assessment of the friction factor term. Yet, friction factor evaluation is not straightforward since traditional fluid-dynamics formulas fail to account for the compressibility effects and are only valid when low Mach numbers are attained, which is often not the case. A numerical model implementing the non-isoentropic compressible Fanno flow theory is presented. A friction factor correlation is proposed, based on the results of a large set of CFD simulations used for calibrating the numerical model. The model is then used for characterizing micro air vent geometries under different operating stagnation pressures and temperatures. The vents characterization is finally employed for the quasi-static assessment of the mass flow rate through the vents, and of the air pressure in the mould during a typical moulding process.

2015 - A fast algorithm for Direct Numerical Simulation of natural convection flows in arbitrarily-shaped periodic domains [Relazione in Atti di Convegno]
Angeli, Diego; Stalio, Enrico; Corticelli, Mauro Alessandro; Barozzi, Giovanni Sebastiano
abstract

A parallel algorithm is presented for the Direct Numerical Simulation of buoyancy-induced flows in open or partially confined periodic domains, containing immersed cylindrical bodies of arbitrary cross-section. The governing equations are discretized by means of the Finite Volume method on Cartesian grids. A semi-implicit scheme is employed for the diffusive terms, which are treated implicitly on the periodic plane and explicitly along the homogeneous direction, while all convective terms are explicit, via the second-order Adams-Bashfort scheme. The contemporary solution of velocity and pressure fields is achieved by means of a projection method. The numerical resolution of the set of linear equations resulting from discretization is carried out by means of efficient and highly parallel direct solvers. Verification and validation of the numerical procedure is reported in the paper, for the case of flow around an array of heated cylindrical rods arranged in a square lattice. Grid independence is assessed in laminar flow conditions, and DNS results in turbulent conditions are presented for two different grids and compared to available literature data, thus confirming the favorable qualities of the method.

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 - Heat transfer along the route to chaos of a swaying thermal plume [Relazione in Atti di Convegno]
Angeli, Diego; Corticelli, Mauro Alessandro; Fichera, A; Pagano, A.
abstract

Detailed analyses have been recently reported on the low order dynamics of a thermal plume arising from a horizontal cylindrical heat source concentric: to an air-ﬁlled isothermally cooled square enclosure, together with those of the related ﬂow structures, in the limit of the 2D approximation. In particular. within the range of O < Ra < 3 RaL-T, With Ram corresponding to the loss of stability of the stationary buoyant plume, the entire evolution from a periodic limit cycle (P1) to the birth of chaos through a period»doubling cascade has been fullyexplored. With this respect, special attention has been given to the window of quasiperiodic dynamics onto a T;-torus that is observed to separate the monoperiodic dynamics from the biperiodic dynamics onto a P1 and a Pg-liniit cycle, respectively. The results of these analyses hint at the bimodal nature of the overall dynamics. in general, and of the subharmonic cascade, in particular, which are still under investigation. Although relevant on a dynamical perspective, a with a main reﬂection on the laminar-turbulent transition, the observed oscillations appear to be characterised by comparable amplitudes and to be determined by similar evolutions of the ﬂow pattern evolutions, so that their role on the overall heat transfer rate is expected to be marginal. Vi/'ithin this frame, the present study aims at reporting the inﬂuence played by the observed dynamics of the thermal plume and of the [low structures on the global heat transferrate. In particular, the aim is the assessment of the correlation between the Rayleigh number and the average Nusselt number on the cylinder surface, as well as the effect on the latter of the observed series of bifurcations.

2015 - Optimization of a finned concentric pipes heat exchanger for industrial recuperative burners [Articolo su rivista]
Cavazzuti, Marco; Agnani, Elia; Corticelli, Mauro Alessandro
abstract

A numerical application is presented in which a finned concentric pipes heat exchanger is simulated by means of CFD, and optimized by the Nelder and Mead simplex downhill optimization algorithm. The heat exchanger parameterization takes into consideration the main geometrical aspects of the exchanger under different operating conditions. The work originates from an industrial problem related to heat recovery issues in recuperative burners, in which air is pre-heated by the exhaust gas before entering the combustion chamber. Such a device allows for an in situ and more efficient heat recovery from exhaust gases, also reducing both the sizing of the heat recovery system downstream to the furnace, and the burner fuel consumption. It is found that the fine tuning of just a few geometrical parameters can result in a sensible enhancement of the exchanger efficiency.

2015 - Optimization of recuperative burners for industrial kilns through CFD simulation [Relazione in Atti di Convegno]
Agnani, Elia; Cavazzuti, Marco; Corticelli, Mauro Alessandro
abstract

An optimization of the shape of a recuperative burner for industrial furnaces for tiles production is presented. The aim of the study is the maximization of the energy recovery from exhaust gas across a heat exchanger in order to pre-heat the combustion air. The study is carried out by means of CFD simulations. Eleven geometric parameters have been chosen and varied individually in an introductory sensitivity analysis. Useful information on the parameters influence have been thus obtained. Due to the large grid size and computing times, a direct optimization has been deemed unfeasible for our purpose. In its place, a fine tuning of the solution has been achieved by investigating the parameters interactions and finding a rather linear superposition of the effects. A reduction of the burner fuel consumption of almost 5% has been attained without affecting the markers of the product firing quality, such as the temperature profile on the tiles floor along the kiln room.

2014 - Appearance of quasiperiodicity within a period doubling route to chaos of a swaying thermal plume [Relazione in Atti di Convegno]
Angeli, Diego; Corticelli, Mauro Alessandro; Fichera, A; Pagano, A.
abstract

The birth, evolution and disappearance of quasiperiodic dynamics in buoyancy-driven flow arising from an enclosed horizontal cylinder are analysed here, by numerical means, in the limit of the 2D approximation. The governing equations are solved on orthogonal Cartesian grids, giving special treatment to the internal, non-aligned boundaries. Thanks to the adoption of a high level of re finement of the Rayleigh number range, quasiperiodicity was observed to emerge from a periodic limit cycle (P1), and to turn into its omologous orbit with doubled period (P2), eventually evolving into a classical period-doubling route to chaos, for further increases of the Rayleigh number. The present study gives a deeper insight to what appears to be an imperfect period doubling bifurcation through a quasiperiodic T2-torus. The approach used is based on the classical tools for time series analysis. The distribution of the power spectral densities is used to search for and characterise the existence of relations between the frequencies of the P1, T2 and P2 dynamics. The topology of the orbits, as well as their evolution within the quasiperiodic window, are analysed with the aid of phase space representation and Poincar è maps.

2014 - I codici commerciali per la Termofluidodinamica Computazionale [Capitolo/Saggio]
Barozzi, Giovanni Sebastiano; Corticelli, Mauro Alessandro; Levoni, Paolo
abstract

Si affrontano alcune problematiche pratiche connesse all'impiego dei codici CFD commerciali

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 - CFD analyses of Syngas-fired industrial tiles kiln module [Articolo su rivista]
Cavazzuti, Marco; Corticelli, Mauro Alessandro; Gianluca, Masina; Roberto, Saponelli
abstract

Industrial kilns for ceramic tiles production demand thorough control of the firing parameters to ensure uniform product quality. A given temperature profile must be imposed along the kiln length, while spanwise temperature profile should be as uniform as possible at the tiles level at any location. Due to special needs in emerging markets, interest is growing towards the use of gases produced by gasification processes as an alternative to methane. This requires specific burner design and proper re-calibration of the firing parameters. In the present work, computational fluid dynamics is used to analyse an industrial kiln section for different fuels, nominal burner powers, and burner nozzle diameters. The results are given in terms of temperature and velocity fields in the kiln room, and temperature distributions over the tiles floor. It is shown that a sensible combination of the three parameters investigated can lead to satisfactory results, even with gases having poor heating value.

2013 - CFD analysis of a syngas-fired burner for ceramic industrial roller kiln [Articolo su rivista]
Cavazzuti, Marco; Corticelli, Mauro Alessandro; A., Nuccio; B., Zauli
abstract

Kiln burners for industrial tile production are usually fuelled by methane gas. However, the interest towards the use of coal or synthesis gases is rapidly increasing, mainly due to the opening of important markets in developing countries. The widely variable chemical composition of these fuels demands the gas burner to be adapted on case-by-case basis, since the firing parameters are strictly fixed, to guarantee the required temperature distribution within the kiln. In this context, computational fluid dynamics analysis represents a very convenient alternative to the traditional design based on experiments. In this article three-dimensional numerical predictions are presented for a syngas-fired burner. Three different fuels, two burner layouts and two burner nominal power are considered. Temperature, velocity and oxygen mass fraction distributions are discussed, and general design lines for low lower heating value gas burners are extracted.

2012 - Analysis of the bifurcating orbits on the route to chaos in confined thermal convection [Relazione in Atti di Convegno]
Angeli, Diego; A., Pagano; Corticelli, Mauro Alessandro; A., Fichera; Barozzi, Giovanni Sebastiano
abstract

Bifurcating thermal convection flows arising from a horizontal cylinder centred in a square-sectioned enclosure are studied numerically, with the aim of achieving a more detailed description of the sequence of transitions leading to the onset of chaos, and obtaining a more precise estimate of the critical values of the main system parameter, the Rayleigh number Ra. Only a value of the geometric aspect ratio A of the system is considered, namely A = 2:5, for which a period-doubling cascade was previously observed. Results give evidence of new and interesting features in the route to chaos, such as a window of quasiperiodic flow and the detection of high-order period orbits.

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 - 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 - Numerical analisys of Weakly turbulent mixed convection flows in a horizontal pipe [Relazione in Atti di Convegno]
Errico, Orsola; Angeli, Diego; Barozzi, Giovanni Sebastiano; Stalio, Enrico; Corticelli, Mauro Alessandro
abstract

Weakly turbulent developing flows in a heated horizontal pipe are investigated numerically, focusing on the effects of mixedconvection, and for two different thermal boundary conditions (BCs), the uniform heat flux condition and the uniform walltemperature condition. The Reynolds number, based on the pipe diameter and bulk velocity, is set equal to Re = 5750 and the molecular Prandtl number Pr = 12. For the sake of comparison, the Grashof number values GrH = 3×108 and GrT = 2.3×1010 are chosen for isoflux and isothermal boundary conditions, respectively. Turbulence is modeled by using alternative RANS approaches. Four RANS models are considered, namely the realizable k-e (RKE), the renormalization-group k-e (k-e RNG), the Gibson’s q-z model, and the Shear-Stress Transport k-w model (k-w SST). Results allow to discriminate the performance ofthe different turbulent models and give hint on the effects of the buoyancy induced flow over the leading forced component.The effect of the thermal boundary condition is finally discussed.

2011 - Bifurcations of Natural Convection Flows from an Enclosed Cylindrical Heat Source [Articolo su rivista]
Angeli, Diego; A., Pagano; Corticelli, Mauro Alessandro; A., Fichera; Barozzi, Giovanni Sebastiano
abstract

A numerical analysis of transitional natural convection from a confined thermal source is presented. The system considered is an air-filled, square-sectioned 2D enclosure containing a horizontal heated cylinder. The resulting flow is investigated with respect to the variation of the Rayleigh number, for three values of the aspect ratio A. The first bifurcation of the low-Ra fixed-point solution is tracked for each A-value. Chaotic flow features are detailed for the case A = 2.5. The supercritical behaviour of the system is investigated using nonlinear analysis tools and phase-space representations, and the effect of the flow on heat transfer is discussed.

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 - Routes to chaos in confined thermal convectionarising from a cylindrical heat source [Relazione in Atti di Convegno]
Angeli, Diego; A., Pagano; Corticelli, Mauro Alessandro; Barozzi, Giovanni Sebastiano
abstract

Natural convection ows arising from a horizontal cylinder centred ina square-sectioned enclosure are studied numerically. The sequence of bifurcations marking the transition of base fixed-point solutions to unsteady, chaotic ows is followed for increasing values of the Rayleigh number, and for two values of the enclosure aspect ratio, A. It is observed that, for the lower A-value, the route to chaosis triggered by a supercritical Hopf bifurcation, followed by a sequence of period- doublings, while, for the higher A-value, the symmetry of the system is broken by a pitchfork bifurcation, with periodic orbits originating from both branches, and eventually approaching chaos, exhibiting features typical of blue-sky catastrophes.

2011 - Spectral response data for development of cool coloured tile coverings [Articolo su rivista]
Libbra, Antonio; L., Tarozzi; Muscio, Alberto; Corticelli, Mauro Alessandro
abstract

Most ancient or traditional buildings in Italy show steep-slope roofs covered by red clay tiles. As the rooms immediately below the roof are often inhabited in historical or densely urbanized centres, the combination of low solar reflectance of tile coverings and low thermal inertia of either wooden roof structures or sub-tile insulation panels makes summer overheating a major problem. The problem can be mitigated by using tiles coated with cool colours, that is colours with the same spectral response of clay tiles in the visible, but highly reflecting in the near infrared range, which includes more than half of solar radiation. Cool colours can yield the same visible aspect of common building surfaces, but higher solar reflectance.Studies aimed at developing cool colour tile coverings for traditional Italian buildings have been started. A few coating solutions with the typical red terracotta colour have been produced and tested inthe laboratory,using easily available materials. The spectral response and the solar reflectance havebeen measured and compared with that of standard tiles.

2011 - THREE-DIMENSIONAL TRANSITIONAL BUOYANCY-INDUCED FLOWSFROM A HORIZONTAL ISOTHERMAL CYLINDER IN A PERIODIC ENCLOSURE [Relazione in Atti di Convegno]
Angeli, Diego; Corticelli, Mauro Alessandro; B., Niceno
abstract

The study presents a preliminary study of three-dimensional transitional natural convection flows, generated by a confined thermal source. The system considered is a periodic enclosure of square cross-section, containing a horizontal cylindrical source, placed in central position. The heat carrier fluid is air with Prandtl number Pr = 0:7. For such system, transition from steady-state tounsteady, chaotic flow has already been widely investigated under the 2D assumption, with respect to the variation of the Rayleighnumber and aspect ratio A. The numerical scheme is based on a second order finite-volume discretization of the Navier-Stokesequations, solved on orthogonal Cartesian grids. Internal boundaries non-aligned with the grid are subjected to special treatment by means of an original technique belonging to the class of Immersed Boundary Methods. Five computations for selected (Ra;A) couples are carried out for comparison with previously obtained 2D results in the transition range. A first hint is provided at the degree of validity of the 2D assumption for the detection of bifurcative dynamics, and the overall quality of the computational technique is evaluated successfully.

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 - Flow Transitions and Bifurcations of Buoyancy-induced Flows from an Eclosed Cylindrical Heat Source [Relazione in Atti di Convegno]
Angeli, Diego; A., Pagano; Corticelli, Mauro Alessandro; A., Fichera; Barozzi, Giovanni Sebastiano
abstract

The study presents a numerical analysis of the dynamics of transitional natural convection flow regimes, generated by a confined thermal source. The system considered is a 2D enclosure of square cross-section, containing a horizontal cylindrical source,placed in central position. The heat carrier fluid is air with Prandtl number Pr = 0:7. The resulting flow is investigated withrespect to the variation of the Rayleigh number, based on the minimum gap width H between the cylinder and the enclosurewalls. Three values of the aspect ratio A are considered (A = 2:5; 3:¯3; 5;). The numerical scheme is based on a second orderfinite-volume discretization of the Navier-Stokes equations, solved on orthogonal Cartesian grids. Internal boundaries nonalignedwith the grid are subjected to special treatment. The first bifurcation of the low-Ra fixed-point solution is tracked foreach A-value. The transition to unsteady, chaotic flow is detailed for A = 2:5. The supercritical behaviour of the system isinvestigated using nonlinear analysis tools and phase space representations of the computed time series, and the effect of the flow features on heat transfer is discussed.

2010 - Flow Transitions and Bifurcations of Buoyancy-induced Flows from an Enclosed Cyindrical Heat Source [Relazione in Atti di Convegno]
Angeli, Diego; A., Pagano; Corticelli, Mauro Alessandro; Barozzi, Giovanni Sebastiano
abstract

This study presents a numerical analysis of the dynamics of transitional natural convection flow regimes, generated by a confined thermal source. The system considered is a 2D enclosure of square cross-section, containing a horizontal cylindrical source, placed in a central position. The heat carrier fluid is air with Prandtl number Pr = 0.7. The resulting flow is investigated with respect to the variation of the Rayleigh number, based on the minimum gap width H between the cylinder and the enclosure walls. Three values of the aspect ratio A are considered (A = 2.5; 3.3; 5). The first bifurcation of the low-Ra fixed-point solution is tracked for each A-value. The transition to unsteady, chaotic flow is detailed for A = 2.5. The supercritical behaviour of the system is investigated using nonlinear analysis tools and phase space representations of the computed time series.

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 - A comprehensive review on buoyancy-induced flow transitions in horizontal annuli [Relazione in Atti di Convegno]
Angeli, Diego; Barozzi, Giovanni Sebastiano; Corticelli, Mauro Alessandro
abstract

The main mechanisms of transition of buoyancy-inducedflows in horizontal annuli are reviewed, based on the availableliterature. Both experimental and theoretical studies areconsidered. The different scenarios for the evolution of theflow regimes and temperature patterns are tracked, for increasingvalues of the Rayleigh number, Ra. The occurrenceof various instability and bifurcative phenomena is pointedout, and linked to other relevant parameters, such as the radiusratio, R and the Prandtl number, Pr. The effect of theaxial dimension is also considered. Finally, possible futureresearch issues on the subject are briefly hinted at.

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 - 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 - 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 - Optimization of heat exchanger enhanced surfaces under turbulent conditions [Relazione in Atti di Convegno]
Cavazzuti, Marco; Angeli, Diego; Corticelli, Mauro Alessandro; Barozzi, Giovanni Sebastiano
abstract

The optimization of heat transfer enhancing surfaces for compact heat exchangers is discussed.The heat transfer passages are parameterized through Bézier curves, and the optimum choice of the parameters is sought using both multi-objective and single objective optimization techniques. The objectives of the optimization are the maximization of the heat transfer rate and the minimization of the pressure drop encountered by the fluid crossing the passage. The objectives are evaluated in nondimensional form in terms of the Nusselt number and the friction factor. The investigation is carried out by means of CFD analyses, the fluid flowing in the passages is air, and turbulent flow is assumed. Two different turbulence models (namely, k- and k-!) are adopted in the optimization processes and the effect of the choice of the turbulence model on the optimization outcome is discussed.

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 - I codici commerciali per la Termofluidodinamica Computazionale [Capitolo/Saggio]
Barozzi, Giovanni Sebastiano; Corticelli, Mauro Alessandro; Levoni, Paolo
abstract

Si affrontano alcune problematiche relative all'utilizzo dei codici commerciali per la CFD

2008 - Influence of the Prandtl Number on Buoyancy-Induced Flow and Heat Transfer from an Enclosed Cylindrical Heat Source [Relazione in Atti di Convegno]
Angeli, Diego; Corticelli, Mauro Alessandro; Barozzi, Giovanni Sebastiano
abstract

A numerical study of the natural convection flow arising from a confined thermal source is presented. The physical systemconsidered is a 2D enclosure of square cross-section, containing an isothermal horizontal cylindrical source. The heating body iscentred in the enclosure, and the resulting flow is investigated with respect to the effect of the Prandtl number, for different valuesof the Rayleigh number and of the aspect ratio. The numerical scheme is based on a second order finite-volume discretization ofthe Navier-Stokes equations, solved on orthogonal Cartesian grids. Internal boundaries non-aligned with the grid are subjectedto special treatment. The work focuses on the onset of steady and transitional flows. The asymptotic flow and thermal patternsare investigated, as well as the heat transfer performance of the system

2008 - Optimization of a buoyancy chimney with a heated ribbed wall [Articolo su rivista]
Cavazzuti, Marco; Corticelli, Mauro Alessandro
abstract

Heat and mass transfer in natural convection vertical channels was investigated by means of two-dimensional CFD simulations aided by optimization algorithms. The channel was immersed in air, enclosed between an adiabatic smooth wall and an isothermally heated ribbed wall. The ribs were perpendicular to the fluid flow and their height, width, pitch, thermal conductivity and lateral wall inclination were variable. Also the smooth heated wall channel was studied and compared with the ribbed one. The existence of an optimal channel width for a given channel height and rib geometry was shown. A sensitivity analysis was carried out for the ribbed and the smooth channels. Optimization was applied to the ribbed channel problem in order to maximize the heat and the mass transfer through a multi-objective genetic algorithm. It was found that the presence of the ribs penalizes the channel performance so that no ribbed channel over-performed the smooth one.

2008 - Optimization of heat exchanger enhanced surfaces through multi-objective genetic algorithms [Articolo su rivista]
Cavazzuti, Marco; Corticelli, Mauro Alessandro
abstract

Heat transfer enhancing surfaces are of interest for a wide range of industrial applications. Theaim of this paper is to provide a robust automated method for the design of two-dimensionalenhanced surfaces. Multi-objective optimization algorithms are employed: the competing objectivesaddressed are the maximization of the heat transfer and the minimization of the pressuredrop for Re = 1000 and Pr = 0:74. The surfaces are parameterized with Bézier curves anda finite volume solver is used for the cfd analysis. The optimization is based on different algorithmsused sequentially. Finally, a robust design assessment analysis is carried out on twoconfigurations.

2008 - Turbulence Models comparison in heat exchanger enhanced surfaces optimization [Relazione in Atti di Convegno]
Cavazzuti, Marco; Corticelli, Mauro Alessandro; Barozzi, Giovanni Sebastiano
abstract

In this paper the problem of the optimization of heat transfer enhancing surfaces is faced. The surfaces are parameterized usingBezier curves and solved with a finite volumes CFD code. The optimization is based on three different algorithms used in cascade:MOGT, MOGA-II and simplex for non-linear optimization. The Reynolds number is based on the average velocity and hydraulicdiameter of the channels and is set to 1000, the Prandtl number is 0:744. The same optimization process is carried out twice usingtwo different turbulence models: k-e RNG with enhanced wall treatment and k-w SST with low Reynolds number correction to theturbulent viscosity. It is found that the differences in the optimum channel shapes are significant and even that the same channelcan give quite different results being solved with a turbulence model or another. Though, from the results of the two optimizationprocesses, the rules of thumb we can infer on which elements a channel needs in order to have a certain performance, are almostthe same.

2007 - Appendice di Deriva I.A.C.C.: Soluzione Numerica Turbolenta [Relazione in Atti di Convegno]
Levoni, Paolo; Corticelli, Mauro Alessandro; Barozzi, Giovanni Sebastiano
abstract

Il presente lavoro si propone di testare le potenzialità di un codice CFD Navier-Stokes ai volumi finiti nella soluzione delcampo idrodinamico relativo ad un’appendice di deriva per imbarcazioni a vela da competizione. In particolare, è stata studiata una configurazione deriva-bulbo I.A.C.C. (International America’s Cup Class), avvalendosi del codice industriale Fluent 6.2 (©ANSYS Inc.). Il complesso comportamento operativo di un sistema di tale tipologia presenta diversi fenomeni idrodinamici di difficile previsione numerica; pertanto il sistema descritto è stato ritenuto un significativo test case per la valutazione delle diverse tecniche di simulazione. I risultati ottenuti sono stati confrontati con dati sperimentali reperiti in letteratura.Sono state esaminate le prestazioni di diversi modelli di turbolenza R.A.N.S. (Reynolds Averaged Navier Stokes), sia di tipo eddy viscosity che Reynolds stress, e del più complesso modello DES (Detached Eddy Simulation). Le simulazioni sono state effettuate avvalendosi di griglie di calcolo di diversa risoluzione, al fine di poter utilizzare in maniera ottimale sia formulazioni low-Reynolds che high-Reynolds. Le comparazioni numerico-sperimentali hanno evidenziato l’idoneità di ciascuno schema alla soluzione del sistema fluidodinamico in oggetto, l’accuratezza ed il relativo onere computazionale.

2007 - Radiation heat transfer effect on natural convection in asymmetrically heated vertical channels [Relazione in Atti di Convegno]
Cavazzuti, Marco; F., Pinto; Corticelli, Mauro Alessandro; E., Nobile
abstract

Heat and mass transfer in vertical channels with a heated ribbed wall is investigated numerically and the results coming from two different CFD codes are compared. The codes are based on finite volume (Fluent 6.2) and on finite element approach (COMSOL Multiphysics) respectively. The channel is two dimensional, is set in vertical position and it is bounded by a heated ribbed wall facing an adiabatic smooth wall. The effects of the aspect ratio, the temperature difference between the heated wall and the ambient, the thermal conductivity of the ribs and the emissivity of the heated wall are considered. The results show that small aspect ratios and low thermal conductivity ribs have a negative effect on heat and mass transfer. High temperature differences and high emission coefficients for the heated wall, on the contrary, lead to a strong enhancement of the channel heat and mass transfer.

2007 - Ricerca di mine mediante termografia infrarossa: analisi dell’influenza dell’umidità superficiale [Relazione in Atti di Convegno]
L., Tarozzi; Muscio, Alberto; Corticelli, Mauro Alessandro; Barozzi, Giovanni Sebastiano
abstract

Il problema dell’individuazione di una mina antiuomo sotterrata è estremamente complesso e di difficile soluzione. Attualmente, la ricerca manuale mediante sondino ad asta costituisce l’approccio più efficace per le attività di bonifica di un’area minata, ma comporta tempi estenuanti e pericoli notevoli per il personale addetto. È quindi evidente la necessità di sviluppare tecniche alternative. Fra queste, si presenta molto interessante la ricerca mediante termografia infrarossa.Questo studio si inserisce in un filone di ricerca da tempo avviato presso il Dipartimento di Ingegneria Meccanica e Civile di Modena, vertente sullo sviluppo di metodologie di indagine che consentano di prevedere ed incrementare l’affidabilità della ricerca di mine antiuomo tramite termografia all’infrarosso. In questa sede, l’analisi ha riguardato l’effetto dell’umidità superficiale del suolo sulla segnatura termica della mina, cioè sul contrasto tra temperatura superficiale del terreno sopra la mina e temperatura superficiale del terreno circostante. Si è a tal scopo impiegato un apparato sperimentale sviluppato nel corso di precedenti attività di ricerca, che consente di riprodurre con scala spaziale e temporale ridotta il comportamento termico un campo minato e le condizioni ambientali che lo caratterizzano. Gli esperimenti svolti hanno mostrato che l’umidificazione del terreno può incrementare notevolmente la segnatura termica della mina e può essere quindi sfruttata per aumentare le probabilità di individuazione.

2007 - Scale reduction in modeling landmine detection by IR Termography [Articolo su rivista]
L., Tarozzi; Muscio, Alberto; Corticelli, Mauro Alessandro
abstract

A method has been proposed to reproduce in the laboratory experiments of infrared landmine detection with reduced length- and time-scale. In this work, the method is verified experimentally. Models of landmines are purposely built by a rapid prototyping technique. The surface response of the soil-landmine system is then monitored by an infrared camera. Preliminarily, the response measured above full-scale models is cross-checked against that measured above actual landmines. Full-scale and reduced-scale models are subsequently tested outdoors and in the laboratory, respectively. The measured distribution and time-evolution patterns of surface temperature are eventually compared, in order to assess the reliability of the scale reduction method.

2007 - Solar reflecting tile coverings for traditional South-European Buildings [Relazione in Atti di Convegno]
L., Tarozzi; Muscio, Alberto; Corticelli, Mauro Alessandro
abstract

An effective solution to summer overheating of buildings is provided by “cool roofs”. These are building coverings with high reflectance to solar radiation and high emittance in the infrared range. They have been investigated extensively in the U.S.A., where certification procedures have already been developed by independent bodies, and certified products are commercially available.Common cool roof products have white or very light colors. As a result, they are difficult to use in most ancient or traditional south-European buildings, which typically have steep-slope roofs covered by red clay tiles. On the other hand, in places like the historical centers of Italian and other Mediterranean cities the rooms immediately below the roof are often inhabited, so that the relatively low solar reflectance of tile coverings makes summer overheating a major problem. This can be effectively addressed by using tiles coated with “cool colors”, that is colors with the same spectral response of clay tiles in the visible, but highly reflecting in the near infrared range, which includes about half of solar radiation. Cool colors can yield the same visible aspect of common building surfaces, but much higher solar reflectance.In the aim of verifying the potential of cool color tile coverings, an investigation was started at the DIMeC. Materials for cool color coating were analyzed in the laboratory, verifying their radiation properties as a function of composition and pigment content. Prototypes of red roof tiles have been built using easily available materials with solar reflectance almost twice that of conventional tiles.

2007 - Thermographic analysis of flow distribution in compact heat exchangers for a Formula 1 car [Articolo su rivista]
E., Caffagni; Levoni, Paolo; M., Piraccini; Muscio, Alberto; Corticelli, Mauro Alessandro; Barozzi, Giovanni Sebastiano
abstract

A non-intrusive approach is investigated to calculate the internal flow distribution in heat exchangers. In particular, the liquid flow rate can be determined in each tube of an air-liquid finned-tube heat exchanger. A purposely designed test bench impresses a sudden change of temperature of the liquid flowing through the heat exchanger. The thermal transient that follows is monitored by a thermographic camera. This measures the rise of surface temperature along each tube. The temperature evolution pattern is then correlated to the flow rate in the tube by simple mathematical processing. The heat exchanger is tested in still air. Modification is not required. The approach is tested on heat exchangers for a F1 race car, with encouraging results. (c) 2006 Elsevier B.V. All rights reserved.

2006 - Experiments on scale reduction in infrared landmine detection [Abstract in Atti di Convegno]
Muscio, Alberto; L., Tarozzi; Corticelli, Mauro Alessandro
abstract

A method has been proposed to reproduce in the laboratory the heating and cooling cycles of a soil with a buried land-mine. The method allows the length-scale and time-scale of the experiments to be drastically decreased. This is achieved by dimensional analysis of the thermal problem. A preliminary confirmation of the used approach was obtained with simplified tests [1-3].In the present work, the method is verified experimentally. Models of different types of land-mine are produced for this purpose. Full-scale and scaled-down models are built by a rapid prototyping technique, using materials with thermal properties similar to those of the actual land-mines.The response of the soil surface is monitored during the thermal cycles by an infrared camera. Preliminarily, the surface response measured above full-scale models is cross-checked against that measured above actual land-mines. Full-scale and scaled-down models are then tested outdoors and in the laboratory, respectively. The measured distribution and time-evolution patterns of surface temperature are eventually compared, in order to assess the reliability of the scale reduction method.

2006 - Experiments on scale reduction in infrared landmine detection [Relazione in Atti di Convegno]
Muscio, Alberto; L., Tarozzi; Corticelli, Mauro Alessandro
abstract

A method has been proposed to reproduce in the laboratory experiments of infrared landmine detection with reduced length- and time-scale. In this work, the method is verified experimentally.Models of landmines are purposely built by a rapid prototyping technique. The surface response of the soil-landmine system is then monitored by an infrared camera. Preliminarily, the response measured above full-scale models is cross-checked against that measured above actual landmines. Full-scale and reduced-scale models are subsequently tested outdoors and in the laboratory, respectively. The measured distribution and time-evolution patterns of surface temperature are eventually compared, in order to assess the reliability of the scale reduction method.

2006 - Optimization of a natural convection vertical channel with a heated ribbed wall [Relazione in Atti di Convegno]
Cavazzuti, Marco; Corticelli, Mauro Alessandro; E., Nobile; G., Tanda
abstract

Heat transfer and mass flow rate in a natural convection vertical channel was investigated using a CFD code coupled with anoptimization dedicated software. The channel was considered bidimensional and set in vertical position, immersed in air, witha heated wall at uniform temperature condition, the other wall being adiabatic. The channel was open at the bottom and at thetop to allow the natural circulation of the ambient air. The heated wall was filled with ribs whose height, width, pitch, thermal conductivity and side wall inclination were variable. The analysis proceeded through the following steps: a) results validation versus schlieren experiments [1]; b) performance comparison: ribbed versus smooth configuration; c) smooth channel sensitivity analysis; d) ribbed channel sensitivity analysis; e) ribbed channel DOE sampling; f) ribbed channel optimization through genetic and simplex algorithms, aiming at average heat transfer and mass flow maximization. In the first steps the existence of an optimal channel width was investigated; the results coming from the latter steps clearly show the importance of the rib height: higher ribs strongly disturb the air stream leading to a performance drop.

2006 - Studio Numerico e sperimentale della convezione naturale da cilindri orizzontali a basso numero di Rayleigh [Relazione in Atti di Convegno]
Corticelli, Mauro Alessandro; Angeli, Diego; D., Ambrosini; D., Paoletti; A., Ponticiello
abstract

Nel presente lavoro si indaga il fenomeno della convezione naturale originata in aria da cilindri orizzontali di piccolodiametro, in regimi a basso numero di Rayleigh. Le analisi sono condotte sperimentalmente e numericamente. Particolareattenzione è riservata al transitorio di innesco della convezione stessa. La parte sperimentale è caratterizzata dall'utilizzo dimetodi ottici, strumenti versatili e potenti per ottenere misure termiche in convezione senza alterare il campotermofluidodinamico. Le simulazioni numeriche si avvalgono di una metodologia di Direct Numerical Simulation, sviluppataspecificatamente per applicazioni di convezione naturale e implementata su griglie cartesiane. I risultati ottenutinumericamente e sperimentalmente sono quindi confrontati fra loro e con i dati esistenti in letteratura.

2005 - Analisi numerica del flusso convettivo instazionario originato da sorgente termica in cavità chiusa [Relazione in Atti di Convegno]
Angeli, Diego; Levoni, Paolo; Corticelli, Mauro Alessandro
abstract

Il lavoro intende esaminare il comportamento di due diversi codici di simulazione CFD nella soluzione del flusso confinato, instazionario, generato da un cilindro riscaldato, in regime di convezione naturale. Nello specifico, l’obiettivo della ricerca consiste nell’analisi delle analogie e delle differenze operative tra le tecniche di soluzione numerica e nella conseguente individuazione dei limiti di applicabilità dei due codici, nell’ambito della specifica tipologia di flusso, al variare dei parametri caratteristici del sistema; particolare attenzione è stata posta sulla previsione e interpretazione della tipologia di moto verso il quale il campo cinetico e termico evolvono, al variare del numero di Rayleigh.Vengono presentati i risultati di simulazioni bidimensionali effettuate mediante un codice industriale ed un codice DNS (Direct Numerical Simulation), sviluppato specificatamente per la soluzione del campo di moto in regime di convezione naturale.Le analisi prevedono valori crescenti del numero di Rayleigh, parametro caratteristico del sistema, e denotano flusso completamente laminare, per bassi valori di Ra, e transizione del campo di moto, per valori di Ra maggiori.Le soluzioni generate dai due codici dimostrano accordo soddisfacente, pur essendo riscontrabili sensibili differenze, sia in termini di precisione e accuratezza, che di tempi di calcolo.

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 analysis of flow distribution in compact heat exchangers for a Formula 1 car [Abstract in Atti di Convegno]
E., Caffagni; Levoni, Paolo; Muscio, Alberto; Corticelli, Mauro Alessandro; Barozzi, Giovanni Sebastiano; M., Piraccini
abstract

THERMOGRAPHIC ANALYSIS OF FLOW DISTRIBUTIONIN COMPACT HEAT EXCHANGERS FOR A FORMULA 1 CAR

2004 - A Numerical Investigation on Convective Accelerometer [Relazione in Atti di Convegno]
Barozzi, Giovanni Sebastiano; C., Bussi; Corticelli, Mauro Alessandro
abstract

Aim of this paper is to investigate an innovative, low – cost, non-intrusive technique for measuringan arbitrary acceleration vector, belonging to a reference plane. The technique is based on freeconvection and allows computing the acceleration magnitude as a function of the temperatureimbalance across four sensors, located within a cavity. The dual-axis convective accelerometermakes use of the relationship existing between the Grashof number and the acceleration vector. Thetechnique shows good linearity, sensitivity and frequency response. The use of a four-sensor clusterallows obtaining the acceleration direction. The shape and the size of the enclosure, as well as thelocation and the number of sensors considerably affect the response of the system. Therefore, aparametric analysis is carried out by numerical simulation. Finally, some hints are provided for thedesign and the tuning of the measuring device. The numerical simulation is carried out using afinite-volume-based ‘projection method’, accurate to the 2nd order in both space and time.Some hints for the designer are finally given based on the dimensional analysis of the device.

2004 - A fast Cartesian scheme for unsteady heat diffusion on irregular domains [Articolo su rivista]
Barozzi, Giovanni Sebastiano; C., Bussi; Corticelli, Mauro Alessandro
abstract

A numerical integration method is presented for the treatment of transient heat conduction problems. A Cartesian formulation is developed that is suitable for the treatment of irregular domains under general boundary conditions. The qualities of the scheme are demonstrated, in terms of both accuracy and computational efficiency, by comparison with analytical and numerical solutions. Results for the basic two-dimensional annular geometry show that the method has nearly second-order accuracy in space and time, at least in simple cases. Finally, a complex multiconnected domain is considered, to test the method performance under more severe conditions, including the presence of multiple length scales. The numerical experiment demonstrates that the numerical scheme is efficient, stable, and convergent.

2004 - Analisi termografica delle maldistribuzioni in uno scambiatore di calore per vetture di Formula 1 [Relazione in Atti di Convegno]
M., Piraccini; Muscio, Alberto; Corticelli, Mauro Alessandro
abstract

In uno scambiatore di calore compatto liquido-aria, la portata di liquido deve distribuirsi uniformemente tra le cannette parallele che costituiscono la massa radiante dello scambiatore. Ciò si ottiene adottando collettori d’immissione e di estrazione del liquido opportunamente conformati, la cui progettazione può essere oggi effettuata, con elevato livello di dettaglio, mediante simulazione numerica. La verifica sperimentale della qualità del progetto è però impegnativa, poiché è possibile formulare valutazioni quantitative sull’omogeneità di distribuzione del liquido refrigerante soltanto ricorrendo a complesse procedure sperimentali ed alla realizzazione di prototipi dello scambiatore opportunamente preparati. Per questo motivo, gli studi sperimentali sono generalmente limitati alla misura di parametri di prestazione globali come, ad esempio, l’efficienza complessiva dello scambiatore.In questo lavoro si presenta una tecnica di misura non intrusiva che consente di stimare, senza dover apportare modifiche allo scambiatore analizzato o eseguire elaborazioni sofisticate dei dati sperimentali, la portata in ognuna delle cannette della massa radiante di uno scambiatore liquido-aria a fascio tubiero alettato. La tecnica è basata sull’analisi del transitorio di riscaldamento che consegue all’immissione nello scambiatore, inizialmente a temperatura ambiente, di una portata di liquido a temperatura molto più elevata. Infatti, la velocità di riscaldamento della parete delle varie cannette, rilevabile mediante termografia infrarossa, può essere correlata alla velocità e, quindi, alla portata del liquido che fluisce all’interno delle cannette stesse.

2004 - Analysis of the impact of surface heat transfer on a new modification of the Angstroem’s method [Relazione in Atti di Convegno]
C., Bussi; Corticelli, Mauro Alessandro; Muscio, Alberto
abstract

A new modification of the Angstroem’s method for thermal diffusivity measurement has been developed. This relies on the propagation of harmonic thermal waves with mean value equal to the ambient temperature. The diffusivity is evaluated by relatively simple processing of temperature data, acquired by infrared thermography.The evaluation is based on a mathematical model, in which the heat transfer coefficient at the specimen surface is assumed to be constant. This work is aimed at verifying that assumption. In particular, the effects of natural convection in air are investigated theoretically by numerical simulation. A strategy to improve the test procedure is finally outlined.

2004 - CFD ananlysys onf the impact of convection in a new modeification of the Ångstroem’s method [Relazione in Atti di Convegno]
Levoni, Paolo; Muscio, Alberto; Corticelli, Mauro Alessandro; Barozzi, Giovanni Sebastiano
abstract

measurement was developed. Its novelty is that harmonic thermal waves with mean value equal to the ambient temperature are induced in the specimen by a purposely developed source. This allows estimating the diffusivity by relatively simple processing of surface-temperature data.The estimate is based on a mathematical model, in which the unknown coefficient of surface heat transfer is assumed to be uniform and constant. The coefficient can thus be eliminated by combining information from amplitude decay and phase velocity of the thermal waves.This work is aimed at verifying the assumption of uniform and constant heat transfer coefficient. A parametric analysis is performed by CFD simulation of the test system.

2004 - Experiments of thermographic landmine detection with reduced size and compressed time [Articolo su rivista]
Muscio, Alberto; Corticelli, Mauro Alessandro
abstract

Infrared thermography is a promising technique for the detection of buried landmines. Its effectiveness is not yet satisfactory, but it can presumably be improved by means of proper data-processing tools. The development of these tools, however, necessitates large amounts of reference data. On-field experiments are required to generate reference data, but they can be very demanding, since it is arduous to control the thermal problem outdoors and all over a whole day. In view of that, a method was developed to reproduce in the laboratory, with reduced size and duration, experiments of thermographic mine detection. The method was devised by the dimensional analysis of the governing equations, for which a generalized formulation is presented, and it was implement by a purposely built apparatus, which allows taking into account the directional properties of the solar radiation. A few test cases with reduced scale are reported here, to show the potential of the proposed experimental approach.

2004 - I Codici Commerciali [Capitolo/Saggio]
Barozzi, Giovanni Sebastiano; Corticelli, Mauro Alessandro; F., Inzoli
abstract

Il capitolo analizza le problematiche collegate all'utilizzo de codici commerciali o industriali in termofluidodinamica

2004 - Influenza della convezione e dell'irraggiamento nella misura della diffusività termica mediante una nuova variante del metodo di Angstroem [Relazione in Atti di Convegno]
C., Bussi; Muscio, Alberto; Corticelli, Mauro Alessandro; Barozzi, Giovanni Sebastiano
abstract

Una nuova variante del metodo di Angstroem consente di stimare, attraverso un’analisi relativamente semplice di misure termografiche nell’infrarosso, la diffusività termica di un materiale solido. La diffusività è correlata alle modalità con cui un’oscillazione termica si propaga in un campione del materiale in esame. La semplicità dell’analisi è conseguenza del fatto che l’oscillazione termica applicata al campione, prodotta tramite un dispositivo appositamente sviluppato, è perfettamente armonica e con valore medio pari alla temperatura ambiente.La procedura di stima della diffusività è basata su una formulazione matematica, in cui si assume costante ed uniforme il coefficiente di scambio termico sulle superfici del campione esposte all’aria. Sotto tale ipotesi, la determinazione del coefficiente di scambio termico, che è in generale incognito, è superflua ai fini della determinazione della diffusività.In questo lavoro si riportano i risultati di un’analisi parametrica dei fenomeni di scambio termico superficiale, effettuata tramite metodi numerici e volta, da una parte, a verificare l’ipotesi di uniformità del coefficiente di scambio termico, dall’altra, ad investigare approcci atti a minimizzare l’impatto dei fenomeni convettivi sull’accuratezza della stima della diffusività.

2004 - Land-mine detection by infrared Thermography: reduction of the size and duration of the experiments [Articolo su rivista]
Muscio, Alberto; Corticelli, Mauro Alessandro
abstract

The effectiveness of infrared thermography applied to the detection of abandoned land mines is not yet acceptable. It can probably be improved, however, by computerized processing of the thermal images. This requires reference data, which must be provided mainly by experiments. A method is presented here, by which the heating and cooling cycles of a soil with a buried land mine can be replicated with reduced size and duration. The reference data acquired in the laboratory can be associated to realistic on-field tests by simply stretching the space and time scales. This will permit to reproduce indoors, quickly and effortlessly, the outdoor conditions of any place where the detection of buried land mines must be performed. In this paper, the general thermal problem is described, and the proposed method is comprehensively explained. The results of computer simulations and some laboratory tests are finally reported for validation.

2004 - Modellazione di transizione dello strato limite con modelli di turbolenza R.A.N.S. [Relazione in Atti di Convegno]
Levoni, Paolo; Corticelli, Mauro Alessandro; Barozzi, Giovanni Sebastiano
abstract

le tecniche numeriche di simulazione termofluidodinamica CFD godono di una notevole diffusione, ma l’onere computazionale che la soluzione diretta dell’equazione di Navier-Stokes comporta (Direct Numeric Simulation), ha determinato un significativo incremento di popolarità dell’approccio R.A.N.S., specialmente in ambiente industriale.Tuttavia nei codici Navier-Stokes industriali non sono stati ancora implementati i modelli tridimensionali di transizione attualmente disponibili, in quanto essi non risultano ancora sufficientemente accurati ed affidabili; pertanto risulta indispensabile, nell’ambito della progettazione navale di barche a vela, la definizione di una tecnica semi-empirica per la riproduzione del fenomeno, finalizzata ad una più realistica valutazione dell’azione tangenziale.A tale scopo è stato analizzato il sistema elementare rappresentato da una lastra piana in assenza di gradiente di pressione nella direzione del flusso, in relazione ad una serie di test sperimentali reperiti in letteratura, effettuati con differenti valori dell’intensità di turbolenza asintotica, quindi con diverse posizioni della zona di transizione

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 - Mine detection by infrared thermography: reduction of size of the experiments [Abstract in Atti di Convegno]
Muscio, Alberto; Corticelli, Mauro Alessandro
abstract

A very promising technique for the detection buried land-mines is infrared thermography. In particular, the presence of a mine can be associated to a specific pattern in the temperature of the soil surface measured by a videothermographic camera. The pattern is induced by the interaction of the daily heating and cooling cycles with the thermal anomaly introduced in the ground by the mine.The specific effectiveness of the thermographic mine detection can be increased by exploiting computerized data-processing tools such as neural-networks, genetic algorithms, or the fusion of dual-band data, to enhance and identify the thermal signature of the mine. The development and ‘training’ of these tools, however, as well as the optimization of the detection equipment and procedure, require a large amount of reference data.Simulations are powerful tools to generate reference data, as they allow fast and inexpensive parametrical analyses. Unfortunately, computer models cannot take care of all the variables influencing a real-world problem and, furthermore, they need a proper calibration. On the other hand, performing parametrical analyses by on-field experiments can be long and challenging, since in an outdoor test environment and along the 24-hour long day period it is arduous to control selectively the phenomena that influence the thermal problem, especially the weather conditions.In view of this, the main objective of the present work is to develop a method by which the cycles of heating and cooling of the soil can be replicated in the laboratory with a reduced scale, either in time or in space, but obtaining measures that can be directly correlated to realistic on-field tests. The result is sought through the dimensional analysis of the equations governing the thermal problem, and it is verified by computer simulations and experiments.

2003 - Osservazioni critiche sull'utilizzo di modelli di turbolenza R.A.N.S. e relative condizioni al contorno in applicazioni di idrodinamica esterna [Relazione in Atti di Convegno]
Levoni, Paolo; Corticelli, Mauro Alessandro; Barozzi, Giovanni Sebastiano
abstract

Il presente lavoro si propone di testare le potenzialità di modelli di turbolenza di tipo RANS, nell’ambitodell’analisi idrodinamica bidimensionale di un profilo laminare, immerso in un flusso stazionario a bassa intensità diturbolenza; tale sezione, di caratteristiche e prestazioni note, è rappresentativa delle tipologie di geometrie utilizzatenel design delle appendici di imbarcazioni a vela da competizione.Scopo della ricerca è definire i limiti di applicabilità e l’accuratezza predittiva delle tecniche di discretizzazione aivolumi di controllo e dei modelli di turbolenza kε-RNG, kω-SST e Spalart-Allmaras, implementati nel codiceindustriale FLUENT, versione 6.0; si intende inoltre evidenziare l’importanza che in questa tipologia di sistemiriveste una oculata scelta delle condizioni al contorno, e come queste influenzino il campo di turbolenza.Il confronto tra risultati numerici e dati sperimentali evidenzia il buon livello di accuratezza che questemetodologie permettono di raggiungere con un costo computazionale ragionevole, sia in termini di potenza che ditempi di calcolo

2003 - Ricerca di mine mediante termografia infrarossa: riduzione della scala degli esperimenti [Relazione in Atti di Convegno]
L., Tarozzi; Muscio, Alberto; Corticelli, Mauro Alessandro
abstract

Una tra le tecniche più promettenti per la ricerca di mine è la termografia infrarossa. Mediante metodi termografici è infatti possibile rilevare l’anomalia che si produce nella distribuzione di temperatura in superficie per effetto dell’interazione dei cicli termici giornalieri e della discontinuità introdotta da un mina sotterrata.Questo lavoro è focalizzato sullo sviluppo di strumenti di indagine che consentano di prevedere ed incrementare l’affidabilità della ricerca di mine mediante termografia infrarossa. Uno di questi è costituito da un modello matematico del comportamento termico del terreno e della mina, in quanto esso permette di compiere studi estensivi con tempi e costi relativamente ridotti. La sua messa a punto è quindi un obiettivo di questa ricerca.D’altra parte, un modello non è da solo sufficiente allo svolgimento di un’indagine completa ed esaustiva, in quanto non può contemplare tutte le variabili che influenzano il problema reale e, inoltre, richiede un’adeguata calibrazione. In questa ottica, l’obiettivo primario del presente lavoro è lo sviluppo di un metodo atto a consentire la riduzione della scala del problema nel tempo e nello spazio, al fine di rendere più veloce e semplice la pratica sperimentale. In particolare, si vogliono scalare il periodo caratteristico, che nella realtà è pari a ventiquattro ore, e le dimensioni dell’ambiente di prova, ottenendo tuttavia risultati correlabili direttamente con il caso reale. Il fine ultimo è riprodurre rapidamente e agevolmente in laboratorio le condizioni ambientali di qualsiasi luogo in cui si debbano ricercare mine mediante termografia infrarossa.

2003 - Simulazione di moti di convezione naturale all'interno di una cavità confinata contenente una sorgente termica [Relazione in Atti di Convegno]
Barozzi, Giovanni Sebastiano; C., Bussi; Corticelli, Mauro Alessandro
abstract

In questo lavoro viene presentato un modello di calcolo per lo studio dei moti di convezione naturale presenti all’interno di cavità chiuse di forma arbitraria, riscaldate da sorgenti interne sempre di forma arbitraria. Lo scopo è quello di fornire uno strumento per l’integrazione diretta delle equazioni del moto,nella loro forma instazionaria adimensionale. Tale strumento è, in ultima analisi, finalizzato allo studio delle modalità di scambio termico diffusivo – convettivo all’interno di cavità chiuse.In questo articolo è presentata una soluzione originale, finalizzata all’integrazione numerica del campo di moto, attraverso una discretizzazione ai volumi finiti su griglia cartesiana, all’interno di geometrie complesse. Lo schema di calcolo proposto è quindi applicato allo studio di due problemi di scambio termico convettivo, per i quali sono dati sperimentali e risultati numerici ottenuti attraverso codici di calcolo tradizionali. L’analisi dei risultati locali e dei coefficienti globali di scambio termico conferma l’accuratezza del metodo di calcolo.

2002 - Caratterizzazione del funzionamento di dispositivi per ventilazione forzata mediante termografia infrarossa [Relazione in Atti di Convegno]
G., Severi; Muscio, Alberto; Corticelli, Mauro Alessandro
abstract

L’impiego crescente di dispositivi attivi di ventilazione in elettrodomestici ed apparecchiature elettroniche di largo consumo rende sempre più interessante lo sviluppo e la messa a punto di metodi di studio che permettano di determinarne ed ottimizzarne le prestazioni – metodi che devono però risultare di implementazione agevole ed economica.Nel presente lavoro si vuole evidenziare la funzionalità di uno specifico metodo di laboratorio basato sulla termografia infrarossa, applicato alla caratterizzazione del flusso d’aria in uscita da un ventilatore tangenziale ad elevato sviluppo assiale. Il fine è l’acquisizione di misure quantitative analoghe a quelle ottenibili mediante tecniche LDV o PIV applicate al medesimo problema, attuando però procedure sperimentali con complessità comparabile a quella di tecniche meno sofisticate. Obiettivo ultimo è la validazione di un modello CFD del ventilatore, realizzato tramite un codice commerciale e destinato all’integrazione in un modello complessivo di un sistema di refrigerazione con elevata efficienza.Il concetto ispiratore è che la diffusione di quantità di moto e la diffusione di energia termica hanno negli aeriformi intensità comparabile. Perciò, se il flusso d’aria prodotto dal ventilatore in esame viene immesso in un ambiente in cui è presente aria in quiete e a inferiore temperatura, si può stabilire una corrispondenza tra la distribuzione di velocità che si instaura in tale ambiente e la distribuzione di temperatura ivi presente, rilevabile mediante termografia infrarossa.

2002 - Comparazione tra Modelli di Turbolenza nello Studio Numerico della Perdita di Carico dovuta ad un Restringimento in un Condotto [Relazione in Atti di Convegno]
Barozzi, Giovanni Sebastiano; Corticelli, Mauro Alessandro; D., Manicardi
abstract

Vengono studiate per via numerica cinque differenti configurazioni geometriche per un sistema composto da un condotto a sezione quadrata che presenta un restringimento a sezione circolare. Lo studio viene svolto utilizzando il software FLUENT, facendo uso, per ciascuna configurazione, dei modelli di turbolenza k- standard, k- RNG e RSM, al fine di valutarne comparativamente le potenzialità ed i limiti, nel contesto della previsione delle perdite di carico concentrate in condotti.L’indagine si riferisce a condizioni di regime stazionario, per un valore del numero di Reynolds pari a 1x105, considerando acqua quale fluido operatore.L’indagine evidenzia una spiccata sensibilità delle soluzioni sia alla conformazione della griglia di calcolo che alla scelta del modello di turbolenza adottato.

2001 - Comparazione tra Modelli di Turbolenza nello Studio Numerico dell’Interazione di Getti Liberi [Relazione in Atti di Convegno]
Barozzi, Giovanni Sebastiano; Corticelli, Mauro Alessandro; Manicardi, D.
abstract

La presente ricerca è principalmente diretta a verificare le potenzialità di pratico impiego dei tradizionali modelli di turbolenza nell’ambito della modellizzazione termofluidodinamica di dispositivi industriali. Vengono qui studiate per via numerica due configurazioni di getti liberi interagenti con valori del numero di Reynolds dell’ordine di 105; entrambe le configurazioni sono costituite da getti in parete sottile emergenti in un ambiente in quiete da un sistema di quattro fori; nel primo caso a sezione circolare e nel secondo a sezione quadrata. Lo studio è stato compiuto con lo scopo di definire i limiti di applicabilità e l’accuratezza predittiva delle tecniche di discretizzazione ai volumi di controllo e dei correnti modelli di turbolenza k-ε standard, k-ε RNG e RSM ed utilizzando il software FLUENT versione 5.0 della Fluent Inc., Lebanon N.H. USA. Si presentano gli esiti delle simulazioni, individuando le zone tipiche dei getti liberi interagenti e altri parametri di interesse industriale.

2001 - Simulazione numerica della convezione naturale in cavità contenenti cilindri riscaldanti in quiete o in rotazione [Relazione in Atti di Convegno]
Corticelli, Mauro Alessandro; Barozzi, Giovanni Sebastiano; Cremaschi, L.
abstract

Lo studio si propone la previsione numerica dei campi termici e dinamici di convezione naturale, prodotti da un cilindro orizzontale a temperatura costante, posto in quiete o in rotazione, immerso in aria, all’interno di una cavità a sezione rettangolare. Le simulazione numeriche sono state condotte utilizzando un codice di calcolo sviluppato per lo studio della convezione naturale in cavità e condotti a sezione rettangolare su griglia cartesiana non uniforme, in cui è stata implementata una procedura che permette di considerare la presenza di oggetti immersi anche a geometria non cartesiana, con una maggiore flessibilità rispetto ai possibili casi analizzabili, mantenendo il tempo di calcolo entro limiti più che accettabili.Il modello è in grado di rappresentare adeguatamente i fenomeni di scambio termico all’interno dei cavità chiuse, sia per regimi stazionari che dipendenti dal tempo.Dove possibile, i risultati sono stati confrontati con quelli ottenuti da prove sperimentali disponibili in letteratura, potendo così convalidare il corretto funzionamento di questo nuovo strumento di analisi.

2000 - Comparazione fra modelli di tubolenza nello studio numerico di getti sommersi [Relazione in Atti di Convegno]
Barozzi, Giovanni Sebastiano; Corticelli, Mauro Alessandro; S., Fantoni
abstract

Si considerano per via numerica due configurazioni di sistemi a getto, l’una relativa all’immissione di aria in ambiente libero, l’altra relativa all’efflusso in ambiente semiconfinato di liquido refrigerante FC77. L’indagine propone il confronto tra i tre modelli di turbolenza k-epsilon standard, k-epsilon RNG e RSM

2000 - Effect of Thermal Boundary Conditions in the Numerical Prediction of Buoyant Flows in a Cavity Containing an Internal Heat Source [Relazione in Atti di Convegno]
Barozzi, Giovanni Sebastiano; Corticelli, Mauro Alessandro
abstract

Buoyancy-induced circulations in a 2D cavity containing rectangular heat source, are predicted numerically. The effect of thermal conditions at the boundaries of cavity is of specific concern. The vertical enclosure walls are in fact isothermal, but different combinations of boundary conditions are admitted at the horizontal walls. These are: isothermal top and bottom walls; top wall isothermal and bottom wall adiabatic; both walls adiabatic. The internal source is isothermal, and air is the working fluid. Results for the three situations are compared for values of the Grashof number, Gr, ranging from 4 x 104 to 4 x 106. The results encompass the stability limit for laminar flow, since a steady-state condition is not obtained at the highest Gr values. It is shown that different thermal boundary conditions give rise to quite different thermal-flow configurations, different heat transfer performances, and, in the high-Gr range, distinctive frequencies of oscillation of the system.

2000 - Natural convection in cavities containing internal sources [Articolo su rivista]
Barozzi, Giovanni Sebastiano; Corticelli, Mauro Alessandro
abstract

Numerical predictions are reported for buoyan- cy-induced circulations in a 2D closed cavity with internal heat sources. Two cases are considered: (A) two vertical plates with uniform heat generation, forming a short vertical channel within the enclosure; and, (B) a rectangular heating block with uniform wall temperature, placed central in the enclosure. Air, with a Prandtl number 0.71, is considered as the working fluid. The vertical enclosure walls are isothermal, while the horizontal enclosure walls are adiabatic. Results are presented for two values of the Grashof number, one below the stability limit for laminar flow, and one well above it. In those latter cases, the long- term behaviour of the numerical solution is time-dependent, i.e. no steady-state can be reached. Heat transfer results are compared with predictions from standard correlations for isolated surfaces.

2000 - Numerical Study of Time-dependent Buoyancy-induced Cavity Flows [Relazione in Atti di Convegno]
Barozzi, Giovanni Sebastiano; Corticelli, Mauro Alessandro
abstract

A 2D square cavity with isothermal horizontal sides and vertical adiabatic sides, is considered, containing a 'virtual' heat source, i.e a heat generating element with permeable boundaries. The horizontal sides of the enclosure are isothermal, and the vertical sides are adiabatic. The source is also square, its size being 1/100 of the cavity side, and is centred in the cavity.The problem is worked out numerically. The solution method is based on control-volume discretizations of the transport equations and a 2nd order projection scheme for time integration.The analysis is directed to demonstrate the potential of the method in the detection of critical values of the leading parameter, the Grashof number, at which some dramatic change in the flow structure occur. The first critical Gr-value, marking the onset of a time-dependent behaviour, is primarily investigated. Air (Pr = 0.71) is considered as the working fluid. The analysis is performed using 31x31, 61x61, and 121x121 grids.The sensitivity of the solution to 'minor' details is also investigated, by treating the same case, but for a 'real' (i.e. with impermeable walls) heat source.

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 - Numerical Simulation of Time-Dependent Buoyant Flows in a Cavity Containing an Internal Heat Source [Relazione in Atti di Convegno]
Corticelli, Mauro Alessandro; Barozzi, Giovanni Sebastiano
abstract

A time accurate finite volume method is used to predict the buoyancy-induced circulations promoted by an isothermal rectangular body in a rectangular enclosure containing air. Three values of the leading non dimensional parameter, the Grashof number, are consider, encompassing the stability limit for steady laminar flow. The long term behaviour and the heat transfer performance of the system are discussed

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 - Numerical simulation of time-dependent buoyant flows in an enclosed vertical channel [Articolo su rivista]
Barozzi, Giovanni Sebastiano; Corticelli, Mauro Alessandro; E., Nobile
abstract

A time-accurate Finite Volume method is used to investigate the two-dimensional buoyant flow in a closed cabinet containing two vertical heating plates. These are parallel, and form a channel at the centre of the cabinet enclosure. The cases of isothermal plates, and of uniform heat generation within them, are both considered for two values, 1 x 10(5) and 1 x 10(7), of the leading non-dimensional parameter, the Grashof number. Air (Pr = 0.71) is considered as the working fluid. Transient and long term thermal and flow behaviours are investigated. Steady-state solutions are asymptotically found at the lower Gr-value. However, time-dependent long-term solutions are predicted at Gr = 1 x 10(7) .

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 - 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 - Modellazione termica del dispositivo di scarico di motori a.c. [Relazione in Atti di Convegno]
Muscio, Alberto; Corticelli, Mauro Alessandro; Barozzi, Giovanni Sebastiano
abstract

Si presenta un modello matematico volto alla previsione delle temperature dei gas e delle temperature di parete di dispositivi di scarico dei gas combusti prodotti da motori ad accensione comandata. Il modello, pur nell'ambito delle forti semplificazioni in esso implicite, consente la previsione del comportamento termico dei condotti di scarico con sufficiente attendibilità, come comprovato da esperienze al banco, eseguite presso il Centro Ricerche FIAT di Orbassano - TO. La tecnica predittiva proposta può consentire un più rapido sviluppo di prototipi dei nuovi sistemi di scarico, atti a meglio soddisfare i limiti di emissione sempre più stringenti proposti dalle normative internazionali.

1993 - A method for the evalutation of the frequencies of incidental events related to the ships traffic inside a port using a statistical approach [Relazione in Atti di Convegno]
Corticelli, M. A.; Vestrucci, P.; Zappellini, G.
abstract

Aim of this paper is to present a semi-probabilistic, semi-deterministic methodology to evaluate the risk of dangerous spills, and related public and environmental hazard, associated to the navigation in a narrow channel-port. The model is based on a Monte Carlo method with variance reduction technique and can simulate different kinds of ship (tonnage, carried substance) and different kinds of routes to reach or to leave the jetties and the port. The basic event probability (operating error) can evolve in collision with: other flowing or moored ships, sand banks, free jetties, dangerous structures. The possible consequences can be spills of hazardous materials, In addition, the probabilistic model evaluates the frequencies of the events at jetty, as onboard fire and/or explosion, load or unload and berth or unberth accidents. The simulation of the system in study can be performed automatically by a package of two programs: the first (input module) accepts the topological and traffic information about the port; the second (simulation module) simulates the port and the traffic using the inputs created by the first. The simulation program can handle sensitivity analysis. Finally, the methodology has been applied to an idealised but realistic situation of channel-port

1993 - Enviromental Source Terms During a Few Reference Accidents Sequences (RAS) of NET/ITER Plant [Articolo su rivista]
G., Cambi; G., Cavallone; M., Costa; Corticelli, Mauro Alessandro; D. G., Cepraga; S., Ciattaglia; R., Passalacqua; S., Paci
abstract

This paper outlines the multi-code methodological approach foreseen to estimate the environmental releases of the activated corrosion/erosion products involved in accidents scenarios of a fusion machine. The radioactive releases associated with some Reference Accident Sequences RAS for the Next European Torus NET have been calculated, based on the following items: Radioactive Inventory RI, Process Source Term PST, and Environmental Source Term EST evaluation. The assessment concerns the NET Basic Performance Phase. Various materials (such as AISI 316L, graphite, beryllium, and boron carbide for the PFC, and water as coolant) and operating conditions (normal running and conditioning) are considered. Different codes have been used and compared. The final environmental releases have been obtained by using RELAP5/Mod.3, FUMO, NAUA-Mod.5 M, and ANITA codes.

1993 - Environment source terms for a few NET plant reference accident sequences [Relazione in Atti di Convegno]
Cambi, G.; Cepraga, D. G.; Cavallone, G.; Costa, M.; Corticelli, M. A.; Di Pace, L.; Passalacqua, R.; Bunz, H.
abstract

The paper presents the Environment Source Terms (EST) associated with some Reference Accident Sequences (RAS) for the Basic Performance Phase of the Next European Torus (NET). Only activated materials have been taken into account as Radioactive Inventory (RI). The activation products have been estimated via ANITA code, using updated neutron cross section library based on REAC-ECN-5 and EAF3 evaluation files. Various materials in the inboard and outboard zones of NET design (AISI 316L, carbon fiber compound, tungsten, and boron carbide for the PFC, and water as coolant) and operating conditions (normal running and conditioning) are considered and assessed. The Process Source Terms (PST) related to some RAS are identified and estimated, by considering the mechanisms leading to RI mobilisation for the RAS of concern (e.g. corrosion/erosion). The FUMO code has been used to estimate the thermal-hydraulic conditions inside the containment for the accident sequences in-vessel and ex-vessel LOCA. The PST transport and deposition in the containment are evaluated by using the NAUA code, running on Personal Computers, in order to define the released fraction from the last containment.

1993 - Visualizzazione ed elaborazione di immagini all'infrarosso per la diagnosi di linee elettriche [Relazione in Atti di Convegno]
Cagnetti, Vittorio; Corticelli, Mauro A.; Vestrucci, Paolo
abstract

L'impiego della termovisione ad alta risoluzione geometrica e termica (HRT) per il monitoraggio delle dispersioni di una linea elettrica ad alta tensione, permette di migliorare notevolmente la capacità diagnostica dei malfunzionamenti con gli associati incrementi di temperatura per effetto Joule (perdite di isolamento degli isolatori,resistenze elettriche anomale nei giunti di ancoraggio, anomalie nei giunti di campata,ecc.), rispetto alla termografia normalmente impiegata, anche ín condizioni di basso utilizzo della linea A.T., in termini di potenza nominale (20% della massima potenza nominale). Vengono riportate alcune immagini, i principali risultati e le considerazioni tratte da alcune campagne di misura

1992 - COMPARE: a COMputer Aided Risk Evalutation package [Relazione in Atti di Convegno]
Barbieri, S.; Commissari, A. M.; Corticelli, M. A.; Malagoli, M.; Rinaldi, G.; Santucci, R.; Stanghellini, S.; Vestrucci, P.
abstract

The representation of the accident consequences is of primary importance in the framework of the risk assessment for industrial areas. The use of maps reproducing the spatial distribution of the involved physical parameters leads to an immediate and synoptic representation of the event consequences. Moreover this kind of consequence report is easily readable also by the non-technical people involved in the decisional process for the public acceptance of industrial plants and for the preparation of the emergency plans. Aim of this paper ís to present the structure of an integrated computer package for the evaluation of industrial accident consequences and their graphical representation over a suitable geographic map of the involved area. The package has the capability to store geographical information about the study site in a digital form (vectorial or raster format). The available meteorological data are associated to the map (with the statistical information about wind speed and direction, stability class, etc.). A more detailed plan of the industrial installation is recorded on the geographic-scale map, where the source points are placed. A data base integrated with the map contains the parameters related to the source points (release height, released substance, flow rate, temperature, pressure, etc.). The user can run a consequence model chosen among a set of possible ones with parameters automatically selected from the system or interactively entered. The output of the calculation is a contour plot of the consequences of the analyzed event on the geographic map. Also numerical results for quantitative analysis are provided. The package runs on PC station platform with colour display and math coprocessor and it is based on CAD system

1991 - Esempi di applicazione della termografia ad alta risoluzione [Monografia/Trattato scientifico]
Cagnetti, V.; Corticelli, M. A.; Santucci, R.; Vestrucci, P.
abstract

Vengono presentati vari esempi di applicazione della metodologia di indagine basata sulla temografia ad alta risoluzione sia spaziale che termica. viene altresì effettuato un breve richiamo sulla fisica della radianza.

1991 - Exact solution to the conjugate problem of nonuniform cooling of fuel rods [Articolo su rivista]
M., Spiga; Corticelli, Mauro Alessandro; M., Trentin
abstract

In this article, the analytical solution to a conjugate heat transfer problem is presented.The temperature distribution of the cladding of a fuel rod is determined, assuming, that the internal heat generation rate is constant, while the local heat transfer coefficient isvariable along the cladding perimeter, because of contact between adjacent rods. The contact occurs in one point (four-cusp channel) or along a line of the wetted perimeter.Due to asymmetric geometry, the heat transfer coefficient depends on the blocking percentage of the channel and vanishes at the points of contact between adjacent rods.The energy balance equation is solved in two regions (h=0 in the former, and h given by a quadratic form in the latter) of the rod perimeter. This quadratic form was deduced by Turner et al. in 1982, solving numerically the fluid-flow problem. The solution of the thermal problem is obtained resorting to the use of Green's function; the results are given in terms of parabolic-cylinder functions.Some graphs are obtained and discussed; the results show satisfactory agreement with other data available in the literature. Numerical work was performed by personal computer.

1991 - Il Package INTER per il calcolo dell'inerzia termica superficiale del terreno, applicazioni ad immagini telerilevate [Monografia/Trattato scientifico]
Cagnetti, V.; Corticelli, M. A.; Santucci, R.; Vestrucci, P.
abstract

Le mappe di inerzia termica del terreno, derivate da riprese nelle bande del visibile e dell'infrarosso effettuate da piattaforme in movimento ad alta quota quali aerei e satelliti, possono fornire utili informazioni Sulle proprietà fisiche e geologiche dello strato superficiale del territorio osservato; tra queste assumono particolare importanza le mappe di umidità del terreno dalle quali è possibile riconoscere: le strutture geo-morfologiche e geologiche, le fratture, le colate laviche, i paleoalvei, i crepacci e le cavità nascoste. Il package INTER consente la stima dell'inerzia termica del suolo a partire dalla conoscenza dei parametri meteorologici, dell'albedo e dalla differenza di temperature tra il giorno e la notte. Il package INTER opera su PC con scheda FG-100-AT della Imaging Thecnology ed utilizza il Software Image-Pro II della Media Cybernetics.

1991 - La perfusione del sistema splancnico in anestesia [Articolo su rivista]
G., Martinelli; S., Baroncini; E., Bernardi; V., Cagnetti; Corticelli, Mauro Alessandro; S., Faenza; G., Frascaroli; F., Petrini; E., Piancastelli; M., Zanello; A., Zanoni
abstract

Mediante una termocamera infrarossa è stata studiata la variazione di temperatura di apparato splancnico di maiali sottoposti a diversi tipi di anestetici ad uso chirurgico.

1991 - Monitoraggio delle dispersioni di una linea elettrica ad alta tensione mediante termografia ad elevata risoluzione. [Monografia/Trattato scientifico]
Cagnetti, V.; Corticelli, M. A.; Santucci, R.; Vestrucci, P.
abstract

L'impiego della termovisione ad alta risoluzione geometrica e termica (HRT) per il monitoraggio delle dispersioni di una linea elettrica ad alta tensione, permette di migliorare notevolmente la capacità diagnostica dei malfunzionamenti con associati incrementi di temperatura per effetto Joule (perdite di isolamento degli isolatori, resistenze elettriche anomale nei giunti di ancoraggio, anomalie nei giunti di campata, ecc.), rispetto alla termografia normalmente impiegata, anche in condizioni di basso utilizzo della linea A.T., ín termini di potenza nominale (20 % della massima potenza nominale). Vengono riportati i risultati ed i commenti di una campagna di misure.

1991 - Programma CARLSON per il calcolo dell'inerzia termica e dell'umidità del suolo, applicazioni ad immagini telerilevate [Monografia/Trattato scientifico]
Cagnetti, V.; Corticelli, M. A.; Santucci, R.; Vestrucci, P.
abstract

Il codice CARLSON permette di calcolare l'evoluzione, dei diversi parametri meteorologici (profili verticali della temperatura del suolo e dell'aria, dell'umidità atmosferica e della velocità del vento) sulla base di un modello sviluppato dal dr. Toby N. Carlson della Pennsylvania State University. Il bilancio termico viene eseguito sulla base di alcune proprietà del suolo (inerzia termica e umidità), anche in condizioni di copertura da vegetazione, che influenzano il trasporto del calore in esso. E' stato possibile instaurare un loop iterativo sulle proprietà fisiche del suolo; in tal modo si può costruire una 'look up table' tramite la quale correlare inerzia termica e contenuto di umidità al salto termico diurno della superficie del suolo

1991 - Termografia ad alta risoluzione [High resolution termovision- HRT] metodi strumenti ed applicazioni [Monografia/Trattato scientifico]
Cagnetti, V.; Corticelli, M. A.; Santucci, R.; Vestrucci, P.
abstract

metodi, strumenti ed applicazioni della termografia ad alta risoluzione

1991 - Uso di una telecamera all'infrarosso termico ad elevata risoluzione per il censimento aereo degli ungulati [Relazione in Atti di Convegno]
Magagmoli, P; Cagnetti, V.; Corticelli, M. A.; Santucci, R.
abstract

Utilizzo di una telecamera all'infrarosso per il censimento degli ungulati

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.

1990 - Cladding Temperature at channel blockages in nuclear reactors [Articolo su rivista]
E., Lorenzini; M., Spiga; Corticelli, Mauro Alessandro; M., Trentin
abstract

The cladding temperature distribution of a nuclear fuel rod in deformed geometry is analytically determined as a function of the azimuthal coordinate, in steady state conditions. The coolant-cladding heat transfer coefhcient is expressed by a parabolic function of the curvilinear coordinate on the wetted perimeter; the deformation provokes the touching on one point or on a line between adjacent rods. The solution to the energy balance equation allows to obtain the temperature as an integral function defined resorting to Green ’s method. The results are compared with reference data available in the literature and give a clear understanding of the temperature dependence on geometrical and physical parameters.

1990 - La rete inversa nel teleriscaldamento urbano [Articolo su rivista]
E., Lorenzini; M., Spiga; Corticelli, Mauro Alessandro
abstract

Vengono confrontate tre possibili configurazioni di reti di teleriscaldamento, con particolare riguardo alla rete inversa, confrontandone costi di impianto e di esercizio

1989 - Numerical Transient Analysis of Parallel and Counter Flow Heat Exchangers [Articolo su rivista]
E., Lorenzini; M., Spiga; Corticelli, Mauro Alessandro
abstract

Numerical transient solutions of parallel and counter current heat transfer processes are obtained by the use of a finite element technique. Solutions provide the one dimensional temperature profile for both fluids of the heat exchangers.The results are verified with steady state and transient analytical or numerical solutions available in literature. The numerical method is applicable to the thermal analysis of anykind of parallel and counter flow heat exchanger with arbitraryinitial and inlet conditions.The main features of the mathematical model, adopted to solve the energy balance equations, is the use of the Galerkin finite elements method to linearize the system of partial differential equations.Very satisfactory results in extremely low computation time arerealized on a medium size computer.

1989 - analisi e comparazioni di reti di teleriscaldamento [Articolo su rivista]
Lorenzini, E.; Spiga, M.; Corticelli, M. A.
abstract

Criteri e metodologie per la progettazione di reti di teleriscaldamento

1988 - An Approach To the Prediction of Cladding Azimuthal Temperature in a Light Water Reactor Four-Cusp Channel [Articolo su rivista]
E., Lorenzini; M., Spiga; Corticelli, Mauro Alessandro
abstract

The temperarure on the outer cladding surface of a light water reactor four-cusp channel hasbeen analytically determined at steady stare and with a linear variation of the coolant/claddingheat transfer coefficient along the curvilinear coordinate. The heat balance equation is transformed into a Sturm-Liouville problem and is solved by the Green's function. The general solution is provided in closed form by using Airy functions of the first and second kinds; hence, the azimuthal temperature distribution is easily amenable to a monodimensional integral of Airy functions. Numerical results are plotted, and the influence of geometric and physical parameters is discussed.

1987 - Dimensionamento delle condotte nelle reti di teleriscaldamento [Articolo su rivista]
Lorenzini, Enrico; Spiga, Marco; Corticelli, Mauro A.
abstract

viene presentato un modello di calcolo per la progettazione di reti di teleriscaldamento, comprendente l'analisi energetica ed economica

1987 - Thermal analysis of the heat exchanger for a spent nuclear fuel storage pool [Articolo su rivista]
E., Lorenzini; M., Spiga; Corticelli, Mauro Alessandro
abstract

A numerical solution is provided to predict the transient temperature distribution of both fluids in the U-tube heat exchanger of a spent nuclear fuel storage pool. A finite element method, with the Galerkin approach, is used to solve the set of five partial differential equations of energy conservations, with arbitrary inlet and boundary conditions. The results are obtained with very low computation time, through a computer program on a CDC 730, which can be easily linked to other thermal hydraulic codes for the storage pool.To show the capabilities of the program, some results are presented, concerning step response and other transient operations of the exchanger.The validation of the method has been performed comparing the numerical results with the exact steady state analytical solutions available in literature; the agreement is very satisfactory.

1986 - LMFBR fuel rod response in natural convection heat decay removal [Articolo su rivista]
E., Lorenzini; M., Spiga; Corticelli, Mauro Alessandro
abstract

This paper describes the fuel rod response in a pool type liquid metal fast breeder reactor, in shutdown natural convection heat removal. The fuel rod response is studied resorting to a finite element technique; the transient temperature and thermal stresses profiles are found.For this aim the code FENHT (Finite Element Nuclear Heat Transfer), has been developed: it is based on a one-dimensional three nodal finite element subdivion of the fuel rod and the solution of the pertinent heat transfer equations is performed by the Crank-Nicholson integration method. Although the strongly non linearities, arising from the thermal properties of the system and from the boundary conditions,the computing time is very low and the numerical solution isreached without undesiderable oscillation

1986 - VELOCITY PROFILES IN THE BUNDLE OF STRAIGHT TUBE STEAM GENERATORS [Relazione in Atti di Convegno]
Lorenzini, E.; Spiga, M.; Corticelli, M. A.
abstract

This paper describes a simplified model to predict the fluid velocity in the external channels of the tube bundle of a vertical once-through steam generator. The model is applied to analyse the three dimensional velocity distribution in a tube bundle cooled by steady state, single phase sodium flow. Results are presented for both a 45 MW and a 225 MW steam generator, including spacer grids and obstructions (to prevent the flow by-pass in the border channels)

1985 - Accident analysis in LMFBR fuel rods by the FENHT code [Articolo su rivista]
E., Lorenzini; M., Spiga; Corticelli, Mauro Alessandro
abstract

This paper describes the code capability related to the safety requirements in nuclear plants. The code solves the non-linear transient heat-transfer problem for the fuel element of a nuclear reactor, in order to simulate any accidental, operational and emergency power transient with arbitrary initial conditions. The temperature distribution in the fuel, gap and cladding is obtained by a finite-element technique based on minimizing the thermal potential with respect to the temperature vector at the nodes of the finite elements. The non-linear differential matricial equation is linearized by an iterative procedure and solved by the Crank—Nicholson method. Also the thermoelastic stresses in the cladding are valued, by the usual Hooke's law. The code has been applied to the analysis of two reference accidents (incidental power transients) occurring in a liquid-metal fast-breeder reactor (LMFBR); the results are reported and briefly discussed

1985 - Validation of the NASGE ThermoHydraulic Code by the PGV Experimental Results [Articolo su rivista]
E., Lorenzini; M., Spiga; Corticelli, Mauro Alessandro
abstract

Translating the steam generator functional requirements intospecific design criteria requires a deep knowledge of thermo fluid dynamical behaviour of both sodium (in the external channels) and water. These features are to be emphasized, since the prediction of speed, pressure, temperature in the sodium and water flow can lead to new design criteria aimed at improving the steam generator performance and avoid dangerous and inefficient operating conditions. Hence it is suitable to have computer codes at one’s disposal, to predict the thermo-fluid dynamics of the fluids in the various operating conditions, for steam generators of any size.This paper is devoted to present a preliminary study on a steam generator code, based on a numerical solution of a channel flow model, predicting the pressure, speed and temperature in any external channel, for water and sodium. The approach used to derive the mathematical model is based on the usual channel flow method.The results are compared with two sets of experimental data performed the first on a plexiglass device by Alsthom Tecnique des Fluides, the second on a real prototype by the Electricite de France; the agreement is very satisfactory.

Università degli studi di Modena e Reggio Emilia

Pubblicazioni