bluuebunny/crossref_metadata_2025_split huggingface dataset:
The influence of Variable Geometry Control on a R290 Ejector Refrigeration System
Authors: Besagni Giorgio , Inzoli Fabio 
Published: April 2022

Abstract
The large-scale deployment of ejector refrigeration systems (i.e., solar-based ejector refrigeration systems), although representing a promising alternative compared with mechanical compressor ones, is hindered due to limitations regarding ejector control modes. Indeed, ejectors are fluid-dynamics controlled devices and, because of their fixed geometry, they operate at their highest efficiency in a narrow range of operating conditions, which is in contrast with the dynamic pressure and temperature levels characterizing real applications. In this context, variable geometry ejectors (VGE) represent a promising solution to increase the flexibility and operation range of this component. The present study aims to extend the present body of knowledge regarding VGE systems, evaluating the impact of a spindle-provided ejector operated with R290 on the performance of the refrigeration system. The analysis has been carried out using an integrated lumped parameter/CFD approach, thus linking the local flow properties and global performances. Different spindle positions have been tested to assess how the different nozzle area ratios affect both the entrainment ratio and the critical pressure. Results showed that increasing primary nozzle area ratio the system can effectively reduce the thermal input, increasing the average COP at the expanse of a lower critical pressure. In conclusion, using a moving spindle control system might ensure an improvement of the ejector performance.
Convective heat transfer CFD analysis of forced flow through a half-stadium serpentine mini-channel at low Reynolds number
Authors: Corti M , Terra C LA , Fanciulli C , Niro A 
Published: April 2022

Abstract
Spiral and serpentine channels are a very interesting solution to enhance heat transfer in small or miniaturized heat exchangers. In order to properly design these devices, of course, it is essential having a good knowledge of heat transfer characteristics of forced flow through this kind of ducts. However, the data base in open literature is rather lacking being investigations concerning flow mainly restricted to Dean number less than 500 and specific geometric parameters. In order to overcome these limits, a CFD analysis of a laminar forced flow through serpentine mini-channels has been started using a commercial code at finite volumes, namely Ansys Fluent. In this paper, after discussing the preliminary CFD analysis carried out on a straight pipe to tune the tool, we present the results on a flow through a half- stadium serpentine mini-channel with Reynolds number ranging between 200 and 2000. As thermal boundary conditions, a uniform wall temperature is assumed on the flat wall of the half-stadium duct, whereas the others are adiabatic. Finally, simultaneously developing flow condition is adopted. Heat transfer performances and pressure drops have been compared with ones in the straight tube, with the same length and hydraulic diameter as the serpentine duct. The results show heat transfer capability increases due to the presence of curvature as well as an earlier transition from laminar to turbulent flow.
Macroscopic model for porous media in oscillating flow for CFD applications
Authors: Di Meglio Armando , Massarotti Nicola , Trombetta Vincenzo 
Published: April 2022

Abstract
In this paper a macroscopic model for porous media in oscillating flow is derived for CFD applications. In non -linear modelling of thermoacoustic devices, their cores, useful for the energy conversion, cannot be, in general, modelled like a traditional porous media through friction factor and Nusselt number correlations, recovered from steady state. In this work the analytical solutions in the frequency domain of the linearized Navier-Stokes equations are spatially averaged for an oscillating flow between parallel plates case to build a macroscopic model of an equivalent porous media through a complex permeability and Nusselt number. The results, obtained by assuming a zero mean temperature gradient, show that there is a good agreement between macroscopic solution of a porous box (representing a parallel plates stack) and the average of the solutions of oscillating flow between parallel plates, both in terms of temperature and velocity fields.
A Eulerian-Lagrangian approach for the CFD analysis of airborne disease transmission in a car cabin
Authors: Grossi G. , Arpino F. , Buonanno G. , Cortellessa G. , Moretti L. , Nagano H. , Stabile L. 
Published: April 2022

Abstract
In indoor environments such as private cars, taxis and public transport, social distance cannot always be applied and virus concentrations can reach high levels. In this paper, a Eulerian-Lagrangian approach is adopted for the transient simulation of aerosol airborne dispersion in a passenger car cabin. The numerical tool, validated by PIV analysis, is applied to study three different scenarios during the respiratory activity. The car ventilation system and the position of the passengers affect the mass of inhaled aerosol and consequently the quality of the passenger compartment air.
Evaluation of the thermal-hydraulic performances of a once-through steam generator in nuclear fusion applications
Authors: Galli Federico , Ciurluini Cristiano , Narcisi Vincenzo , Giannetti Fabio , Caruso Gianfranco 
Published: April 2022

Abstract
After decades of operation in nuclear power plants, Once-Through Steam Generators (OTSGs) were recently proposed for nuclear fusion applications. In particular, they are supposed to be installed in the primary cooling systems of the European Union Demonstration fusion power plant (EU-DEMO). One of the key reactor components is the Breeding blanket (BB). Among the BB concepts that are currently under study, Water-Cooled Lithium-Lead (WCLL) option was considered for this work. The WCLL blanket is divided in two main subsystems, the breeder zone (BZ) and the first wall (FW), each one provided with an independent cooling circuit, named Primary Heat Transfer System (PHTS). Thermal power removed from BB by BZ and FW PHTS is driven to the Power Conversion System (PCS) to be converted into electricity. The thermal coupling is ensured by two OTSGs per system. At the Department of Astronautical, Electrical and Energy Engineering (DIAEE) of Sapienza University of Rome, a simulation activity was carried out to understand the component thermal-hydraulic behavior during DEMO normal operations. For calculation purposes, a full model of the steam generator was prepared by using a modified version of RELAP5/MOD3.3 system code. The computational activity performed allows to preliminary characterize the OTSG thermal-hydraulic performances during both pulse and dwell phases.
Transient analysis of OSU-MASLWR with RELAP5
Authors: Molinari Martina , Narcisi Vincenzo , Ciurluini Cristiano , Giannetti Fabio 
Published: April 2022

Abstract
The present paper deals with the assessment of the original and a modified version of RELAP5/MOD3.3 against the OSU Multi Application Small Light Water Reactor (OSU-MASLWR). The new implemented features regard suitable correlations for the heat transfer coefficient evaluation in helical geometry. Furthermore, two different modelling of the Helical Coil Steam Generator (HCSG) are assessed. In the first approach, HCSG’s primary and secondary sides are collapsed in a single pipe component. In the second model, three equivalent pipes are conceived for the simulation of the three ranks composing the HCSG.
Two different power manoeuvring experiments are reproduced. The simulations highlight a satisfactory agreement in both the transients. Nevertheless, the modified code shows enhanced capabilities in the prediction of the HCSG operation. This is due to the improvements adopted in the modified version of RELAP5/MOD3.3 that allows a better modelling of the dryout phenomena occurring within helical tubes, as well as a better estimation of the primary side heat transfer coefficient. The better agreement of the heat exchange is propagated to the primary system, resulting in a more accurate prediction of the inlet and outlet core temperatures, and primary flow rate.
Effect of non-condensable gas in steam condensation at sub-atmospheric pressure condition
Authors: Giambartolomei G. , Pesetti A. , Raucci M. , Aquaro D. 
Published: April 2022

Abstract
In the International Thermonuclear Experimental Reactor (ITER), a postulated Loss Of Coolant Accident (LOCA) in the Vacuum Vessel (VV) has to be managed with a pressure suppression system working at sub-atmospheric pressure. The operating conditions considerably differ from those experienced in the fission nuclear power plants such as BWR, since the ITER Tokamak works at very low pressure conditions and can withstand a maximum pressure of 0.15 MPa. For this reason, the pressure value must not exceed 10 kPa for a water temperature of 30 °C inside the Vapour Suppression Tanks (VSTs) that are the fundamental components of the Vacuum Vessel Pressure Suppression System (VVPSS). During a LOCA some non-condensable gases (mainly hydrogen and oxygen gases due to the water radiolysis or thermolysis) may be mixed in the steam and this could impair the condensation efficiency. In order to investigate the effects of non-condensable gas on DCC, we conducted a research program funded by ITER Organization at the laboratory of the University of Pisa: we designed and built a small-scale experimental rig to study the steam Direct Contact Condensation (DCC) with the presence of non-condensable gas and simulate the behaviour of a VST. Since DCC can occur with different characteristics, we ran 12 closed mode tests exploring all condensation regimes injecting a certain mass of air with the steam discharged in the subcooled water. The tests started at the saturation pressures corresponding to water temperatures ranging from 40 °C to 80 °C and ended when the free space volume reached the atmospheric pressure. From the analysis of the data acquired during the tests we observed that the condensation efficiency remained higher than 95%. We observed that despite this, the presence of a certain quantity of non-condensable gas has negative aspects on condensation: the condensation regime never reaches stability (the regimes quickly shift towards instability). Furthermore, the presence of air triggers a turbulence of the flow which interferes with the transfer of heat from the steam to the water. Not only the introduction of air into the flow increases linearly the pressure above the water head but its high temperature further contributes to the pressure increase. The air mixed with the flow also forms eddies that can trap the steam and transport it out of the water, preventing it from condensing. Apart from condensation, the most noticeable problem is the rapid increase in pressure inside the condensation tank.
Analysis of an unmitigated 2-inch cold leg LOCA transient with ASTEC and MELCOR codes
Authors: Agnello G , Ederli S , Maccari P , Mascari F 
Published: April 2022

Abstract
The analyses of postulated severe accident sequences play a key role for the international nuclear technical scientific community for the study of the effect of possible actions to prevent significant core degradation and mitigate source term release. To simulate the complexity of phenomena involved in a severe accident, computational tools, known as severe accident codes, have been developed in the last decades. In the framework of NUGENIA TA-2 ASCOM project, the analysis of an unmitigated 2-inch cold leg LOCA transient, occurring in a generic western three-loops PWR-900 MWe, has been carried out with the aim to give some insights on the modelling capabilities of these tools and to characterize the differences in the calculations results. The ASTEC V2.2b code (study carried out with ASTEC V2, IRSN all rights reserved, [2021]), and MELCOR 2.2 code have been used in this code-to-code benchmark exercise. In the postulated transient, the unavailability of all active injection coolant systems has been considered and only the injection of accumulators has been assumed as accident mitigation strategy.
Entropy Generation Analysis on Confined Impinging Slot Jets with Nanofluids in Metal Foam
Authors: Buonomo B , di Pasqua A , Manca O , Nappo S 
Published: April 2022

Abstract
In this paper a numerical entropy generation analysis on confined slot impinging jets made up of a totally filled configuration of metal foam in mixed convection is presented. A two-dimensional domain is assumed and several Peclet numbers (equal to 350, 750, 1500) are considered. Rayleigh numbers is imposed equal to 30000. The employed working fluids are pure water or Al2O3/water based nanofluids. The nanoparticle volume concentrations are in a range from 0% to 4% and the nanoparticle diameter is varied in a range from 20 nm to 80nm. The target surface is characterized by a constant temperature, estimated starting to the value of Rayleigh number. The distance of the target surface is five times greater than the slot jet width. The thermal and fluid dynamic properties of nanofluids are evaluated by a single-phase model method. The model of local thermal non equilibrium (LTNE) is considere in order to simulate the behavior of the metal foam characterized by a number of pores per inch (PPI) equal to 5, 10, 20, 40 and a porosity around 0.90. The data in terms of total global entropy generation related to the thermal and viscous effects are given Results show increasing values of the total entropy generation for increasing values of Peclet number and nanoparticle concentration. This behaviour is more evident at higher Peclet number values. In addition, the total entropy generation increases with the increase of PPI in corresponding to the same porosity value.
Liquid holdup measurement for gas-liquid stratified flows by means of resistive probes and image processing
Authors: Carraretto I M , Colombo L P M , Guilizzoni M 
Published: April 2022

Abstract
Flow patterns exert a fundamental influence on the behaviour of multiphase flows, and they must be brought into play when dealing with their modelling. This is usually done by means of summarizing quantities as the phase holdups and the interfacial area concentration. Many techniques have been designed during the years to measure them, among which the use of probes relying on electrical resistance is one of the simplest and less expensive. While having these points of strength, resistive probes are intrusive devices. This work is therefore devoted to a comparison between liquid height (and derived quantities) measurements – for stratified and stratified-wavy air-water flows – performed using a conventional resistive probe and by means of an image-based technique. Validation of the latter was performed using computer-generated flow images. Then, an experimental campaign was carried out for flows with liquid superficial velocities in the range 0.03 ÷ 0.06 m/s and gas superficial velocities in the range 0.77 ÷ 2.31 m/s. Results showed that the two methods give answers within very few percent of difference, which is more than satisfactory in this field. The results are also in good agreement with some of the most credited literature models and correlations.
Development of an innovative temperature control system in a fermenter: application to the case of the wine industry
Authors: Malavasi Matteo , Cattani Luca , Bozzoli Fabio , Rainieri Sara 
Published: April 2022

Abstract
Temperature is one of the most important parameters influencing the fermentation in wine making process. Indeed, its control during this phase is fundamental to obtain a high-quality product. Fermentation is an exothermic process and for this reason a good cooling system in fermenter tanks is required. The temperature control systems usually adopted are represented by an external cooling jacket in which cold water flows. This system is based on the water circulation which is activated only when a critical temperature in the fermenter is exceeded making the control less precise. In this paper an alternative solution based on heat pipe technology is designed and its feasibility is investigated through the application of its ideal variant. This innovative temperature control system has the advantage to work on continuous mode, thus keeping the temperature in the fermenter more uniform during the whole process. Moreover, the proposed system is fully passive reducing the costs of this process phase. The results of this work demonstrated that the device application could be feasible and that it represents a promising solution.
Heat fluxes distribution and uncertainty in low-Reynolds flow regimes inside a ribbed channel
Authors: Vitali L , Gramazio P , Fustinoni D , Niro A 
Published: April 2022

Abstract
Experimental studies on the local convective heat transfer enhancement induced by ribs in channels are generally carried out in steady state, by imposing a known heat flux on the ribbed surface and subsequently retrieving the convective heat flux by means of a local heat balance, i.e. by subtracting all the non-convective heat fluxes from the source term. Such heat fluxes are retrieved from temperature measurements by means of models, whose complexity can range from simple algebraic expressions to complex simulations. In this context, an experimental technique based on FEM simulations, a radiative model for semi-transparent enclosures, and a filtering technique to retrieve the heat fluxes across the plane of the heated surface has been developed and tested in a 1:10 AR channel, for Reynolds number ranging from 650 to 7500 and a flow of air. This paper presents a discussion on the heat flux distribution as a function of the Reynolds number for a streamwise-pointing chevron (V) rib configuration with 60° angle of attack, with P/e = 20, showing the increasing weight of non-convective heat dissipations as the Reynolds number decreases, and their effect on the uncertainty of the Nusselt number measurement.
Thermo-fluid dynamic resonance in cancer cells
Authors: Grisolia Giulia , Lucia Umberto 
Published: April 2022

Abstract
In the third decade of XX century, Warburg pointed out that cancer cells follow a fermentative respiration process, as a consequence of a metabolic injury. In this paper, we consider this statement in the following way: any cell process requires energy, so, in the cell, a control of the energy conversion can represent a possible control of the cell processes. Engineering thermodynamics is the science that studies the conversion of energy into work. So, thermodynamics could represent a powerful approach to analyse of the energy conversion in the biosystems, for their control. Cells regulate their metabolisms by energy and mass (ions included) flows, and the heat flux occurs by the convective interaction with their environment. Here, we consider fluxes through the biosystems border, their shapes and the characteristic time of thermal interaction with the blood and water, in the cell environment. Moreover, just in relation to time, it is possible to consider the resonance phenomena. Resonance forces natural behaviours of systems, when a wave of a frequency, related to the characteristic time, income to a system. Here, we introduce the biothermodynamic characteristic frequency, which is the characteristic frequency of a biosystem, evaluated by a thermo-fluid dynamic approach, in order to control the fluxes through the cancer membrane, and to force it towards an optimal behaviour, by changing the concentrations of ions, inside and outside of the membrane itself. The result consists in a control of the cellular metabolic processes, and also of the energy available to cancer, for its growth. In this way, the cancer growth rate can be reduced.
Assessment of predictive methods for the heat transfer coefficient during flow boiling of R50 and R170 mixtures
Authors: Ferretto William , Lucchini Andrea , Colombo Luigi P.M. 
Published: April 2022

Abstract
Liquefied natural gas (LNG) is a binary mixture of methane (R50) and ethane (R170). Proper evaluation of the heat transfer coefficient during flow boiling of such a mixture is very important to design LNG facilities. Pure fluid correlations have been tested with and without the adoption of corrections to account for the lowered performance due to mass transfer resistances arising both in the nucleate boiling and in the convective boiling regimes. In total, the prediction of 13 correlations has been compared with a new data set from the literature. Results show that the correction related to nucleate boiling has the greatest impact though, in general, the adoption of the corrections leads to under predict the data.
Experimental investigation of R744 transcritical flow and mixing in the two-phase ejector
Authors: Bodys Jakub , Palacz Michal , Haida Michal , Smolka Jacek , Dziurowicz Damian , Majchrzyk Michal , Nowak Andrzej J. 
Published: April 2022

Abstract
In this work, the laboratory test rig for visualisation of the CO2 ejector is shortly presented. The internal flow structures in the premixing chamber and expansion cone are visualised using two different measurement arrangements, i.e. Particle Image Velocimetry (PIV) system and high-speed camera system. Both systems allow to determine some characteristic features of the R744 flows and propose some important quantities (i.e. expansion and mixing angles) describing expansion and mixing processes. Potentials of those preliminary results for field validation data are also pointed out.
Mechanisms of dropwise condensation on aluminum coated surfaces
Authors: Mirafiori Matteo , Tancon Marco , Bortolin Stefano , Martucci Alessandro , Del Col Davide 
Published: April 2022

Abstract
Dropwise condensation (DWC) is a complex phase-change phenomenon involving the formation of randomly distributed droplets on the condensing surface. The promotion of DWC instead of the traditional filmwise condensation (FWC) is a promising solution to enhance the efficiency of heat exchangers by increasing the condensation heat transfer coefficient. The interaction between the condensing fluid and the surface (wettability) is important in defining the condensation mode. On metallic surfaces widely employed in heat transfer applications, the condensing process occurs in filmwise mode. Ideally, an engineered surface designed to achieve high DWC heat transfer coefficients should present low contact angle hysteresis and low thermal resistance. Among the different available techniques to modify the surface wettability, hybrid organic-inorganic sol-gel silica coatings functionalized with hydrophobic moieties (phenyl or methyl groups) have been identified as a feasible solution to promote DWC on metallic surfaces. In the present paper, different aluminum sol-gel coated surfaces have been tested during DWC of steam in saturated conditions. The realized coatings have been characterized by means of dynamic contact angles and coating thickness measurements. Condensation tests have been performed using a two-phase thermosyphon loop operating in steady-state conditions that allows visualization of the condensation process and simultaneous heat transfer measurements. Heat transfer coefficients have been measured by varying the heat flux, at 106 °C saturation temperature and with vapor velocity equal to 2.7 m s−1. A high-speed camera is used for the visualization of the DWC process.