bluuebunny/crossref_metadata_2025_split huggingface dataset:
The state-of-the-art on Refrigerants
Authors: Cavallini A 
Published: September 2020

Abstract
The two recent global emergencies (stratospheric ozone depletion and global warming) force refrigerating engineers and operators to face a new revolution on the choice of the working fluids for the different applications of refrigeration technology. Chemistry by now runs short of new synthetic products meeting within acceptable limits all the requirements asked for by the different refrigeration applications, and compromise solutions are more and more necessary, involving a limited use of few old-generation fluids, the new family of products HFO and an increased consideration for natural refrigerants. While dealing with these topics, this paper will show how basic thermodynamics can highlight important characteristics of a refrigerant.
Experimental study of a phase change material storage for low-temperature applications
Authors: Besagni G , Croci L 
Published: September 2020

Abstract
Thermal energy storage technologies are matter of intense research and discussion, in the broader framework of decoupling the “demand-side” and the “supply-side”. This topic is of paramount importance to support the large-scale deployment of renewable energy-based technologies in the residential sector, to support the decarbonisation pathways. In this perspective, a promising solution concerns solar-assisted heat pumps. This paper contributes to the existing discussion by developing, building and testing a “pilot-scale” finned-and-tube phase change material storage for solar-assisted heat pumps applications (viz.,low temperature applications, in the range of 20 - 30 °C). The proposed storage unit is tested, under real boundary conditions and it is able to store 65 % higher thermal energy stored compared with an equivalent water storage unit.
Two-Phase Heat Transfer in 4.0 mm Tube Under Different Gravity Conditions
Authors: Lancione Giorgia , Mieko Iceri Daiane , Gugliermetti Luca , Saraceno Luca , Zummo Giuseppe , Bisegna Fabio , Nardecchia Fabio 
Published: September 2020

Abstract
This study aimed to analyze the two-phase heat transfer in a vertical upward flow configuration under different gravity conditions. The facility is a new version of MicroBo (Microgravity Boiling), the working fluid used is perfluorohexane C6F14 and a 4.0 mm aluminum channel is arranged vertically to perform ebullition process. The platform used to get data in microgravity was the parabolic flight, which represents one of the most widely used platforms despite the period of time available to collect data is very short. The analysis of the results has been carried out following two main approaches: the first, ground-flight data comparison, for the study of variable gravity data collected during the 67th ESA campaign of parabolic flight held in November 2017, while the second, ground data analysis, to analyze the data collected on the ground in the ENEA laboratory with the same facility in December 2018. In particular ground – flight data have been analyzed comparing boiling curves at different flow rates, from a minimum of 5.3 l/h up to 17 l/h, in micro, hyper and normal gravity. The operating inlet pressure during experiments has been fixed at 1.6 bar with a heat flux range of 5.4 - 85.6 kW/m2. For what regard ground data boiling curves, with a flow rate of 10 l/h, are shown with a direct flow pattern visualization. The operating pressure has been fixed at 1.3 bar and 1.8 bar with a heat flux range of 2.5 – 94.6 kW/m2. For the latter analysis, it also has been carried out a qualitative study for the validation of the void fraction model, starting from the visualization of the images of flow patterns recorded during the acquisitions.
Experimental analysis of drop-size density distribution during dropwise condensation of steam
Authors: Mirafiori M , Parin R , Bortolin S , Del Col D 
Published: September 2020

Abstract
Dropwise condensation (DWC) has attracted research interest since its first description in 1930 due to the high heat transfer coefficients that can be obtained by promoting this mechanism as compared to the case of filmwise condensation. The modelling of dropwise condensation heat transfer is complex since it must account for droplets nucleation, growth and removal: researchers proposed different methods and the first semi-empirical model was presented in 1966 by Le Fevre and Rose. Their model predicts the total heat transfer across a surface during DWC by estimating the drop-size density distribution and the heat transfer through a single droplet. The goal of the present work is to investigate the large drop-size density distribution during dropwise condensation considering different operating conditions (heat flux and surface coating). In this work, a new illumination system (torus-shaped LED) has been designed and built to allow droplets detection with diameters from millimetres down to few microns. The torus-shaped LED is used as light source for a high-speed camera coupled with microscope lens. The recorded images have been analysed by a homemade software in MATLAB® code, and the measured droplet population has been compared with the theoretical formula proposed by Le Fevre and Rose [1]. More than six million droplets have been detected and an excellent agreement with the Le Fevre and Rose theory has been found.
Water Pool boiling on Aluminum Metal Foams
Authors: Righetti G. , Calati M. , Doretti L. , Hooman K. , Mancin S. 
Published: September 2020

Abstract
With current growth in electronic systems, their physical sizes decrease, and the spacing between components decreases, both the total amount of heat generated and the power density increase significantly. There is a general agreement in the scientific community that current air-cooling technologies are asymptotically approaching their intrinsic limits. Pool boiling is widely used in many different engineering systems, but most of these applications have a common limitation: the maximum heat flux that can be rejected by the cooling systems under safe, reliable, and efficient operation. In this paper experimental data pertinent to deionized water pool boiling across 10 mm thick aluminum foams are presented. Three foam samples with different pore densities, 5, 10, and 40 PPI, yet with an identical mean porosity of 0.92 are tested. Compared to a heated flat plate, the foams offer higher heat transfer area albeit at induced bubble escaping resistance. The tradeoff between these two effects is investigated. Through the use of high speed video camera recording, bubble generation, trajectory and growth rate were analyzed and critically discussed.
Natural convection in a vertical channel with open-cell foams
Authors: Andreozzi A , Bianco N , Iasiello M , Naso V 
Published: September 2020

Abstract
Open-cell foams are promising to enhance heat transfer in many applications, such as electronics cooling. Though heat transfer coefficients are low, natural convection in open-cell foams is used in low-end applications, as consumer electronics or switching devices. In this paper air natural convection in a vertical channel equipped with an open-cell foam, with a symmetric uniform heat flux boundary condition at the vertical sides, is investigated numerically. The foam is modeled as a continuous porous medium under the assumption of Local Thermal Non-Equilibrium (LTNE) between solid and fluid phases. Mass, momentum and energy equations are solved numerically under the appropriate boundary conditions by employing a commercial finite element code. The velocity of the fluid and the temperature of the solid as well as the global heat transfer coefficient, for different thermo-physical properties and morphologies of the foam, and for various channel aspect ratios, are predicted.
Numerical investigation on thermoelectric generators in an exhaust automotive line with aluminium foam
Authors: Buonomo B , di Pasqua A , Manca O , Nardini S 
Published: September 2020

Abstract
In the present paper a two-dimensional convective heat transfer problem in a partially filled channel with metal foam is numerically solved in steady state regime. An external thermoelectric generators (TEG) component is placed on the top surface of the channel. The numerical analyses are accomplished assuming the local thermal equilibrium (LTE) model to simulate the presence of the aluminum foam. The working fluid is exhaust gas with properties equal to the air for fixed temperature of the upper surface of the thermo-electric generator (TEG). The thermophysical properties are assumed temperature independent and the TEG component is considered as a solid with an internal energy generation. The Ansys-Fluent code is applied in order to resolve the governing equations for gas, porous media and TEG. Several mass flow rates of exhaust gas on the inlet section of the channel are considered. Different thicknesses of aluminum foam are assumed into the duct. The foam is characterized by different porosity equal to 0.90, 0.95, 0.97. Moreover, the number of pores per inch also changes and assumes the following values of 5, 20, 40. Results are showed in terms of temperature distributions, pressure drop, thermoelectric efficiency for different exhaust gas flow rates and metal foam characteristics and thicknesses. The results highlight that the use of metal foams significantly increases the heat transfer between the surface of exhaust gas tube and hot gas. Consequently, the effectiveness improves, and it increases between three-ten times with respect to the one for tube without metal foams. It is shown that the pore density does not affect the effectiveness.
Onset of thermal convection in a horizontal porous layer saturated by a power–law fluid
Authors: Celli Michele , Natale Impiombato Andrea , Barletta Antonio 
Published: September 2020

Abstract
A horizontal porous layer saturated by a non–Newtonian fluid is taken into account. The fluid is a Ostwald–De Waele type of fluid. The layer is heated from below while the upper boundary is isothermal. The lower boundary is impermeable and the upper one is free. A fully developed basic throughflow is considered. The basic state is perturbed by employing small amplitude perturbations such that a linear stability analysis is performed. The disturbances are assumed to be normal modes and a system of ordinary differential equations governing the perturbation dynamics is obtained. These ODEs form an eigenvalue problem that is solved numerically: both the neutral stability curves and the threshold values for the onset of convection are presented.
Influence of the convective coefficient on the determination of thermal transmittance through outdoor infrared thermography
Authors: Nardi I , de Rubeis T , Paoletti D , Ambrosini D 
Published: September 2020

Abstract
Several studies and correlations for the convective heat transfer coefficient (CHTC) are available in literature and in handbooks, depending on type of convection, wind speed range or on the test rigs from which they are derived.
The importance of accurate evaluation of CHTC, especially at the building façades, has been highlighted in the recent years, due to the need for reliable measurement of buildings’ heat transfer capability. This study aims at underlining the importance of proper CHTC values for the determination of the building envelope thermal transmittance (U-value) via infrared thermography (IRT). To this scope, firstly an overview on convective heat transfer coefficient is given; then, some CHTC models, chosen from literature, are analyzed at different wind speed classes. Subsequently, such models are employed in two formulas proposed in literature for the U-value measurement via IRT, by using data from previous experimental campaign carried out in controlled environment. Results were compared, and significant deviations were found: one of the employed approaches and formulation is less sensitive to the correlation adopted for the convection expression, amongst those considered and in the wind speed range analyzed. This constitutes an advantage, since one of the weak points of the IRT method is the convection expression itself.
Infrared image processing for local convective heat transfer measurements in rib-enhanced channels
Authors: Vitali L , Gramazio P , Fustinoni D , Vignati F , Niro A 
Published: September 2020

Abstract
In the context of an experimental study designed to retrieve the local heat transfer characteristics in closed channels with ribs in several configurations by IR thermography, a filtering strategy must be adopted to calculate the laplacian of the temperature field, to remove not only Gaussian noise, but also unwanted local features due to the pattern of the conductors of the heater. In this paper, these issues are addressed with a comparative analysis on filtering and interpolation techniques, in particular mean filtering, local surface fitting and cubic smoothing splines, which are carried out by showing their influence on the smoothed thermogram and on the laplacian of the temperature field. The use of cubic smoothing splines gives the best approximation of the temperature field with respect to the mean filter, which alters the temperature field in proximity of the ribs, and to surface interpolation. However, the only filter among those tried that gives meaningful derivatives on the whole image is the mean filter, with a kernel size equal or bigger to that of the spatial feature to be filtered. The resulting derivative also need further filtering to reduce local spikes induced by the filtering operations.
Experimental study of a natural circulation loop and RELAP5-3D analysis
Authors: Bertani C , Falcone N , Bersano A , Azzarone A , De Salve M , Panella B 
Published: September 2020

Abstract
Passive safety systems, which are being largely adopted in advanced nuclear reactors to enhance the safety of the plant, are often based on natural circulation for the decay heat removal and are characterized by the presence of non-condensable gases and pools with stagnant liquid at atmospheric pressure. At the Energy Department of Politecnico di Torino (Italy), the test facility PROPHET has been designed and operated with water in both single-phase and two-phase flow. It consists of a bayonet heat exchanger electrically heated at constant power, a condenser immersed in a pool containing a fixed initial mass of water and the connecting pipes. The effect of loop filling ratio and condenser shell-side level on the system behaviour are here studied. The experimental transients have been analysed in terms of phenomenological windows. Heat losses and the heat sink influence both the time behaviour and the final values of pressure and temperatures in the facility; the filling ratio determines the kind of natural circulation (single-phase or two-phase) and strongly affects the phenomena occurring during the experiments. The experimental results are also compared with the predictions of a RELAP5-3D model. Discrepancies between calculated and experimental values are estimated during the transients in order to evaluate the code prediction capabilities.
Preliminary neutron kinetic – thermal hydraulic coupled analysis of the ALFRED reactor using PHISICS/RELAP5-3D
Authors: Ciurluini Cristiano , Narcisi Vincenzo , Giannetti Fabio , Cretara Luca , Caruso Gianfranco 
Published: September 2020

Abstract
The development of a lead-cooled fast reactor (LFR) demonstrator was proposed, mainly in EU, to investigate the feasibility of an industrial size ELFR (European Lead-cooled Fast Reactor). The demonstrator, called ALFRED (Advanced Lead-cooled Fast Reactor European Demonstrator), consists of a pool-type lead-cooled fast reactor, with a nominal thermal power of 300 MWt. This paper aims to verify the capability of the PHISICS/RELAP5-3D coupled approach to simulate transients of such reactor and to evaluate the effects of accidental scenarios relevant for the safety analysis on the system thermal-hydraulics and on the core power spatial evolution. RELAP5-3D©, developed at Idaho National Laboratory (INL), is a thermal-hydraulic system code, validated for a wide range of transient simulations. The code provides the possibility to simulate innovative working fluids (such as lead and lead alloys) and to use a fully integrated multi-dimensional nodalization. In addition, the need to study complex neutronic systems recommended the development of a new kinetic model allowing the calculation with any number of energy groups and also considering the transport for the angular variations. At this purpose, INL developed PHISICS (Parallel and Highly Innovative Simulation for INL Code System) and its coupling methodology with RELAP5-3D. The simulation activity described in this paper has been focused on the safety analysis of ALFRED reactor assuming the occurrence of two unprotected transient scenarios: unprotected loss of flow (ULOF) and unprotected transient overpower (UTOP). At this purpose, a thermal-hydraulic geometrical scheme of the whole reactor has been developed. The models and the outcomes of the calculations are described and discussed in the paper, highlighting the capability of the coupling approach to obtain results consistent with the ones available in the literature.
Direct condensation of steam in a water tank at sub-atmospheric pressures
Authors: Giambartolomei G , Pesetti A , Lazzeri R , Merello C , Sarkar B , Olcese M , Aquaro D 
Published: September 2020

Abstract
In the nuclear fusion reactor, ITER, the Loss of Coolant Accident (LOCA) in the Vacuum Vessel has to be managed with pressure suppression systems working at sub-atmospheric pressure. The operating conditions differ considerably from those experienced in the fission nuclear power plants such as BWR. The direct condensation at sub-atmospheric conditions is not sufficiently known, therefore, the effectiveness of systems operating at these particular conditions have to be investigated experimentally.
A research program is being carried out at the University of Pisa, funded by ITER, in order to study the steam direct condensation for nuclear fusion reactor conditions. For this purpose, an experimental test facility was designed and built and an extended experimental program was performed. Video cameras were used to visualize the steam condensation at different mass flow rates.
This paper deals with the elaboration of images of the steam jet flowing from a hole in the water. The steam condensation regimes depend on three governing parameters: downstream exit pressure, water temperature and steam mass flow rate per hole. Moreover, the condensation regimes are characterized by different shapes of steam jet.
The image analysis permitted to determine the heat transfer coefficient in the stable condensation regime at sub-atmospheric conditions. The results obtained are compared with those correspondent at steam condensation at atmospheric pressure, emphasizing the great importance of the downstream exit pressure and the subcooling on the steam condensation.
A novel approach for the numerical analysis of waste-to-energy plants
Authors: Arpino F , Buonanno G , Cortellessa G , Costa M. , Dell’Isola M , Massarotti N. , Zuena F 
Published: September 2020

Abstract
In this paper the authors present a simplified 0D-3D approach for modelling operating conditions of a waste-to-energy plant This innovative methodology combines a 0D lumped parameters model, able to describe the processes of solid and gaseous combustion and the heat transfer within the first radiant channel, with a detailed 3D CFD simulation of the thermo-fluid-dynamic field within the plant combustion chamber. Besides, results from the 0D model allow the definition of input data and boundary conditions for detailed 3D CFD simulation of the thermo-fluid-dynamic field within the plant combustion chamber. In this way, the T2S temperature can be determined using a more efficient and complete methodology. The developed numerical tool, does not employ correlations based on empiric observations or on experimental data regressions and, being phenomenological, is generally applicable to any waste-to-energy plant, and is here applied for the characterization of different operating conditions of an Italian WTE. The analysis allows the verification of the constraints imposed by the European legislation on the temperature of the combustion products and the identification of any issues related to the plant operation. Input parameters are determined from measurements and the obtained numerical results are validated against experiments showing a good agreement.
A thermo-economic based method for the design of process heat solar systems
Authors: Franco A , Bertola G 
Published: September 2020

Abstract
In this paper, the perspectives of production of thermal energy for industrial process heat from solar energy are considered. This represents a quite relevant topic for an overall containment of using fossil fuels with the objectives of reducing the impact of fossil fuel use. In particular, the paper outlines a thermo-economic design methodology taking into account the main variables problem (solar source, system architecture, design constraints, load type and distribution, design criteria and optimization criteria). The innovative element of the methodology is the consideration, among the various costs, of an economic penalty given to the operation of the auxiliary boiler. The results of the application in a particular case are shown in the final section of the paper, showing how it could be possible to increase the value of the solar share, up to 80% with respect to the conventional design method, that often limit this value at 60%.
Numerical and experimental study on metamaterials featuring acoustical and thermal properties
Authors: Levi Elisa , Neri Manuela , Pilotelli Mariagrazia , Alessio Piana Edoardo , Maria Lezzi Adriano 
Published: September 2020

Abstract
Metamaterials can be defined as materials which, for their peculiar composition or structure, exhibit characteristics that are not normally found in nature. “Multifunctional” metamaterials could be used to optimise different characteristics at the same time. In this paper the authors try to apply them for thermal and acoustic optimization of external building walls. Thermal optimization consists in obtaining a low transmittance, important in winter, and a low periodic thermal transmittance, important in summer. Acoustic optimization consists in obtaining high sound transmission loss, to respect the law prescriptions, and a good sound absorption coefficient, if possible. In this way should be possible enhance the comfort conditions in buildings and reduce the energy demand for winter heating and summer cooling. The proposed solution consists of several layers with different suitable characteristics: the sequence of the layers has been chosen with particular care. The thermal analysis has been performed by means of a self-developed code based on the ISO 13786 standard. The acoustic behaviour of the single layers has been determined following the procedure given by the ASTM E2611-09 standard using a four-microphone impedance tube and the transfer matrix method has been used for the complete assembly. This preliminary combined study showed encouraging results.