bluuebunny/crossref_metadata_2025_split huggingface dataset:
Experimental investigation of effects of convective heat transfer and thermal performance of impinging jet on a metal plate with porous media
Authors: Khoso A Q , Fareedi A R , Khan H , Buonomo B , Manca O , Nardini S 
Published: June 2024

Abstract
This experimental investigation is aimed to evaluate the effects of convective heat transfer phenomena in an aluminium metal flat disc/plate placed below metal foam using a single round jet of air impinging in a confined region. The Jet impingement technique contains pressurized air, which is configured for certain specific application. It is designed to spray the fluid with the help of a nozzle on the surface of the disc or plate which is being heated or is being cooled. To understand the heat transfer phenomena in a metal plate with metal foams facing round air jet impingement; three metal foams of similar geometries but of different porosities and permeabilities are taken for study. Each experiment is performed with seven different flow rates and at two different heights with two different heat flux values. The recorded measurements are temperatures, pressure differences, flow rates, resistance voltages and currents, and time. The outcomes of the experimental data are analysed and compared results of all four distinct kinds of metal foams with different jet to plate height and at different heat fluxes. It is concluded that heat transfer efficiency may or may not increase depending upon the metal foam used. Overall, the conclusions are extremely useful in engineering.
Sensitivity of an electrical impedance-based sensor for the liquid fraction estimation during melting and solidification inside a vertical rectangular enclosure
Authors: Mira-Hernández Carolina , Mancin Simone 
Published: June 2024

Abstract
Monitoring the liquid fraction in latent thermal energy storages (LTESs) can enable the implementation of smart control strategies for improved performance and increased utilization of renewable energy sources. However, measuring the liquid fraction is challenging because solid-liquid phase change processes occur at nearly constant temperature. The present study explores an electrical impedance-based sensing technique that could become a non-intrusive and accurate alternative to determine the liquid fraction. The study examines the melting and solidification of a phase change material (PCM) inside a vertical rectangular enclosure with an isothermal wall. Two sets of electrodes are located on each of the side walls of the enclosure. Initially, numerical simulations of melting and solidification are performed to generate physically meaningful solid and liquid phase distributions. Then, these phase distributions are used as input for electrical simulations to estimate the response to changes in the liquid fraction of the electrical impedance between electrode pairs in in-line, front-facing and crosswise configurations. Also, the effect of the contrast ratios between the electrical conductivity of the solid and liquid phase on the sensitivity is assessed. The front-facing electrodes are found to have the best performance across a large range of conductivity ratios. The in-line electrodes perform the lowest because the sensitivity drastically decreases as a layer of the more conductive phase starts forming on the wall where the electrodes are located. An improvement in the performance of in-line electrodes is observed when the conductivity ratio is decreased.
Numerical analysis of the energy efficiency of drying a flooded masonry wall by applying a variable drying air temperature profile
Authors: Wasik M , Łapka P 
Published: June 2024

Abstract
The masonry wall initially saturated with moisture and without internal or external water sources was considered to simulate the drying of a wall after a flood. Numerical calculations using the in-house non-equilibrium heat and moisture model were performed to investigate the impact of variable drying air temperature profiles on the drying efficiency of the thermo-injection method. A drying process lasting twelve days was simulated. Based on previous studies, four drying air temperature variation strategies, i.e., jump, stepwise, periodic, and constant temperature (reference), were computed and compared. The drying air temperature profile was changed from 20°C to 60°C with heating intervals of 24 h and different characterization strategies. The jump strategy changed rapidly in a single step. Stepwise one changed by 10°C after each heating interval, and the period strategy changed from 20°C to 60°C or from 60°C to 20°C after each heating interval. Furthermore, the relative humidity of the drying air corresponded to the three seasons in Poland (i.e., winter, summer, and spring) and ranged between 70% and 90% at ambient conditions. It was found that the proposed drying strategies with variable temperature profiles can reduce energy consumption compared to the reference strategy with a constant temperature.
Temperature forecasting for single-phase immersion cooling system based on machine learning
Authors: Pratheek S , Ashwin R S , Balaji C 
Published: June 2024

Abstract
High-heat-flux-density data centres face significant thermal management challenges, particularly those for 5G and AI applications. Elevated processor temperatures lead to frequent thermal throttling and non-uniform thermal stresses, negatively impacting server performance and reliability. This highlights the need for effective thermal management strategies. Machine learning-based temperature prediction algorithms have shown promise in proactively managing the thermal condition of the system. In his study, a Raspberry Pi 4 Model B+ was immersed in mineral oil to simulate the workloads based on cryptography, Fast Fourier Transform (FFT) and data analytics. The discrete wavelet transform technique is used to mitigate the impact of noise interference in the experimental data. The results show that the attention-based LSTM encoder-decoder model (LSTM-ED-Attention) coupled with the entropy minimisation strategy outperformed the baseline LSTM encoder-decoder model by 22, 15 and 20% for prediction horizons of 10, 30 and 60 seconds, respectively.
Thermodynamic analysis of two-fluid, two-phase immersion cooling system for cooling of electronic components
Authors: Krishnadasan V B , Suresh Pratheek , Balaji C 
Published: June 2024

Abstract
Two-phase immersion cooling system is a specialized and increasingly popular method for cooling high-power density electronic components, such as CPUs, GPUs, and other server equipments. In a typical two-phase immersion cooling system, a dielectric fluid is employed for immersing electronic components. The challenge lies in the fact that the fluid chosen often has limited thermal conductivity, hindering effective heat transfer. In a two-fluid immersion cooling system, electronic components are submerged in a dielectric fluid known as the boiling fluid. Within the same tank, a separate condensing fluid is introduced, which is immiscible with the boiling fluid. The condensing fluid, characterized by its lower density and higher thermal conductivity compared to the boiling fluid, enhances heat transfer within the system. In the current study, Novec 7100 serves as the boiling fluid, while deionized water is employed as the condensing fluid. In this work, exergy analysis is conducted to assess and compare the efficiency of a two-fluid, two-phase immersion cooling system in contrast to a single-fluid, two-phase immersion cooling system. Additionally, a comparison is carried out to evaluate how the performance of the system varies under diverse operating conditions. The study is conducted for a maximum heat flux of 12.3 W/cm2 and performance of the system is evaluated at condenser inlet temperatures spanning from 5 to 25 °C. From the investigations carried out, it is seen that the exergy efficiency of the two-fluid system surpasses that of the single-fluid system by approximately 70% under same heat flux and condenser inlet temperature conditions.
Modelling thermal dynamics in intermittent operation of a PEMEL for green hydrogen production
Authors: de les Valls E Mas , Capdevila R , Jaramillo J , Buchholz W 
Published: June 2024

Abstract
Green hydrogen plays a pivotal role in the imminent energy transition, addressing energy storage and electricity generation decarbonization. The European Commission’s hydrogen strategy underscores the goal to install at least 40 GW of green hydrogen electrolysers by 2023. Despite various electrolyser technologies, efficiency improvement and durability enhancement remain challenges, especially considering voltage intermittencies from renewable energy sources. This study emphasizes the impact of thermal gradients within electrolysers due to voltage interruptions, affecting membrane operation and causing premature wear. The study explores methods to minimize thermal gradients, revealing trade-offs between efficiency and durability. A lumped-parameter numerical model is developed and experimentally adjusted to simulate electrochemical and energy transport phenomena. Experimental and numerical results are compared, highlighting the need for a comprehensive thermal management code for effective electrolyser performance. The study addresses the importance of accurately modelling transient thermal responses for both proton exchange membrane electrolysis (PEMEL) and solid oxide electrolysis (SOEL) designs, providing insights for future advancements in thermal management strategies.
Numerical simulation of droplet impact onto heated surfaces below the boiling point
Authors: Saha Rishav , Weigand Bernhard 
Published: June 2024

Abstract
Droplet impact onto heated surfaces is a widespread process in industrial applications, particularly in the context of spray cooling techniques. Therefore, it is essential to study the complex phenomenon of droplet spreading, heat removal and flow distributions during this process. The primary focus of this research centers on the wetting dynamics at a surface temperature below the saturation temperature of the liquid. This study employs a Computational fluid dynamics (CFD) framework to simulate the impact dynamics of a water droplet onto a heated surface. The impact dynamics, spreading, air entrapment and heat transfer in the process are discussed using simulation results. The Direct Numerical Simulation (DNS) tool Free Surface 3D (FS3D), an in-house code at the Institute of Aerospace Thermodynamics, University of Stuttgart, is utilized. The Finite-Volume method is used to solve the incompressible Navier-Stokes equations, and the interface is defined by the Volume of fluid (VOF) method. In this study, the temperature change above the entrapped air bubble formed due to droplet inertia is shown, which can influence the heat removal rate in the process. Therefore, conducting a comprehensive study on the temperature shift caused by the air bubble is crucial.
An advanced numerical radial sub-resolution technique to correct heat fluxes in the vicinity of bubbles at saturation
Authors: Grosso Mathis , Bois Guillaume , Toutant Adrien 
Published: June 2024

Abstract
This work explores the use of a thermal sub-resolution technique applied on coarse grids to better estimate the temperature gradient in the vicinity of a bubble at saturation as part of a DNS-Front-Tracking framework. By refining locally the solution and realigning it with the bubble’s interface normal direction, the temperature and fluxes prediction are notably enhanced. The refined profiles computed by Finite-Difference in a local spherical frame of reference are then transmitted to the fixed grid using several coupling methods both identified from the literature. Coupling methods overriding the fixed grid temperature are interesting in terms of ease of implementation and robustness whereas face fluxes methods are conservative, but they may cause underestimation of quantities and may require local smoothing like neighbouring averaging. In pure diffusion, these coupling approaches show a good agreement with the theoretical Nusselt number profile. However, the quasi-static hypothesis is difficult to satisfy at the beginning of the simulation which causes a permanent bias. Results are promising on a rising bubble case, reducing the error on the heat transfer prediction below 6.5% with a reduction in computation cost by a factor of 1300 compared to a reference simulation.
Experimental study of convective heat transfer in additive manufactured minichannels: the impact of the roughness and Prandtl number
Authors: Kadivar Mohammadreza , Cozzarolo Luca , Kinell Mats , Nogenmyr Karl-johan , Tormey David , McGranaghan Gerard 
Published: June 2024

Abstract
Additive Manufacturing, especially Laser-based Powder Bed Fusion (L-PBF), can fabricate internal channels with enhanced cooling properties. Roughness is a natural consequence of the L-PBF process that can increase flow friction and also influence heat transfer in these cooling channels. While existing literature predominantly explores the impact of roughness on flow friction, less attention has been given to the effects on heat transfer. In this study, a novel experimental setup employing Joule heating was developed to investigate water flow in minichannels fabricated by L-PBF. The impact of roughness and different Prandtl numbers on flow friction and heat transfer was studied. The results indicated that the Nusselt number in rough channels scales with the Prandtl number to the power of 0.8 (Pr
0.8), suggesting greater heat transfer with higher Prandtl numbers for rough channels compared to those of smooth channels. At a specific combination of relative roughness and Reynolds number, the enhancement of heat transfer due to roughness is maximized.
Design of thermal management system for a battery pack with malfunctioning battery: - a numerical parametric study
Authors: Majumder Sayan , Akula Rajesh , Vennela Bommadevara Sai , Balaji Chakravarthy 
Published: June 2024

Abstract
In this study, a hybrid cooling technology comprising phase change material (PCM) and active cooling was employed for a battery pack arrangement with a circular configuration. The numerical model comprised simulated Li-ion batteries made of aluminium, which generate heat, housed within a cylindrical steel casing filled with a PCM. Numerical simulations were carried out using the ANSYS-FLUENT 2023 R2 edition. A comparative study was conducted on various battery configurations, including 4-battery and 6-battery setups, subjected to constant heat loads of 5W and 15W, cyclic heat loads where batteries generate a constant 5W or 15W for 500 seconds within each cycle, followed by a 500-second interval with no heat load, and charge-discharge cycle analyses. In the latter study, three batteries operated at 5W while one malfunctioning battery operated at 15W. Two configurations were tested, including a single pipe and four pipes. Preliminary results revealed that the hybrid cooling system with a single pipe reached a maximum temperature of 90°C for the malfunctioning battery configuration, whereas the four-pipe configuration resulted in a maximum of 56°C before achieving a steady-state condition. These findings underscore the effectiveness of the proposed cooling mechanism, even when handling heat loads exceeding the batteries’ rated capacities.
Numerical investigation on liquid cooling of batteries in phase change materials
Authors: Arumugam A , Buonomo B , Romano P , Manca O 
Published: June 2024

Abstract
The primary focus of this study centres on managing the thermal conditions of the battery systems, addressing the various concerns related to external climatic factors on the vehicle’s performance and heat generation during the battery operation. The major objective of this study is to implement a passive thermal management system using the phase-change materials to model and control the temperature of the rechargeable batteries which are influenced mostly by critical temperature rise and external climatic influences. A numerical simulation involving a three-dimensional, single module model of a rechargeable lithium-manganese dioxide battery is involved. The control mechanism involves the application of the phase change materials within a parallelopiped structure with the battery positioned in the central location and cooled by the surrounding convective tubes through which liquid flows. The module is considered an adiabatic medium in nature. The numerical investigation involves three different C-rates for two different phase change materials RT27 and RT31, which are employed using the Finite volume method using the Ansys-Fluent. The detailed analysis of the surface temperature of the battery, liquid fraction fields and the average temperature attained by the battery module is involved using the two PCM materials.
Sustainable heating and cooling for residential buildings: coaxial ground heat exchangers
Authors: Ahmed F , Massarotti N , Šarler B 
Published: June 2024

Abstract
As the world fights climate change challenges and the soaring demand for energy-efficient solutions, the need for sustainable heating and cooling systems in residential buildings has become paramount. Traditional systems rely on fossil fuels and contribute significantly to greenhouse gas emissions. Ground source heat pumps (GSHPs) have emerged as a promising technology, offering a sustainable alternative to conventional space conditioning systems. Central to the success of GSHPs is the efficient and reliable operation of their ground heat exchangers, with lower installation costs, as a prospective solution for future residential applications. This paper presents a numerical axisymmetric (r-z) finite volume method solution of the thermal performance of coaxial ground heat exchangers (CGHE) that incorporate phase change material (PCM) in the ground for GSHP applications. An analysis of the CGHE with PCM grout is presented, highlighting the advantages of heat exchange performance over normal grouts. The temperature comparison on three different points in the grout with different grouting materials was carried out to analyse the behaviour of different grouting materials during the heat exchange process. The investigation from a temperature point of view showed that the inclusion of PCM in the grouting material improves the thermal performance of the CGHE.
Tracking of the melting front in tube-in-tube latent thermal energy storage heat exchangers
Authors: Van Zele J , Goderis M , Couvreur K , Beyne W , De Paepe M 
Published: June 2024

Abstract
In this study, the shrinking solid regime is investigated in a high aspect ratio tube-in-tube latent thermal energy storage (LTES) heat exchanger by tracking the phase change front evolution. In the setup, water flows through the inner tube as heat transfer fluid (HTF) and the shell contains a paraffin RT35HC as phase change material (PCM). A series of melting experiments have been performed in which the HTF mass flow rate, HTF inlet temperature and initial PCM temperature were varied. During each experiment, the movement of the phase change front was tracked using a camera placed next to the PCM tube. The front position as a function of time follows an S-shape curve. The effect of the operating conditions on the evolution of the phase change front is analysed. It is found that the temperature difference between the HTF and PCM exerts a more pronounced influence on the front position compared to the HTF Reynolds number. Finally, a correlation was developed to determine the temporal evolution of the front position. This research contributes to a deeper understanding of phase change phenomena in LTES systems and the found correlation can be a valuable tool for predicting and optimizing the performance of tube-in-tube LTES heat exchangers.
Design of an ultrahigh temperature liquid metal centrifugal pump for thermal energy storage
Authors: Buznitsky K , Pishahang M , Henry A 
Published: June 2024

Abstract
Liquid metals serve as efficient heat transfer fluids due to their exceptional thermal conductivity and broad temperature range, rendering them well-suited for demanding applications such as nuclear reactors and thermal energy storage. Nevertheless, designing liquid metal pumps poses significant challenges, including chemical compatibility with the containment vessel and various thermomechanical issues. This study focuses on elucidating these challenges and proposing potential solutions through the example of a centrifugal pump designed for handling liquid tin at an extreme operating temperature of 2400°C. To address chemical compatibility concerns, graphite is adopted as both the containment and pump material, presenting novel mechanical hurdles. Key obstacles include accommodating thermal expansion and navigating the intricacies of working with features approaching the grain size of graphite.
Computational fluid dynamics modelling of large-scale bubble columns: from the mono-dispersed to the pure heterogeneous flow regime
Authors: Varallo Nicolò , Mereu Riccardo , Besagni Giorgio , Inzoli Fabio 
Published: June 2024

Abstract
This study proposes a CFD model to simulate large-scale bubble columns operating in different flow regimes. Transient 3-D simulations were performed employing a commercial code (ANSYS Fluent), and the numerical results were compared with available experimental data. The superficial gas velocity ranges between 0.0037 m/s and 0.2 m/s, covering both the mono-dispersed and pure-heterogenous flow regimes, where bubbles coalescence and breakup were modelled. The results have been critically analysed, and the discrepancies between the numerical and experimental results have been deeply commented on, setting the stage for future improvements.
Mixed convection flow over a horizontal plate and the horizontal wake far downstream
Authors: Bábor L , Schneider W , Bozsó E 
Published: June 2024

Abstract
The laminar mixed convection flow over a heated or cooled horizontal plate of finite length is a surprisingly intriguing problem. The hydrostatic pressure jump at the trailing edge and across the wake is to be compensated by induced circulation in the outer potential flow, similar to a plate at a non-zero angle of attack. The mixed convection flows over semi-infinite and finite horizontal plates, respectively, are thus substantially different. As the hydrostatic pressure jump remains finite along the infinitely extended wake, the induced outer potential flow around the plate would grow beyond bounds in a domain extending to infinity. Thus, boundary conditions must be imposed at the boundaries of a finite domain. However, the numerical solution of the Navier-Stokes equations remains a challenging problem due to the lack of appropriate outflow conditions. The traditional outflow condition cannot comply with the finite hydrostatic pressure jump across the wake. Thus, an asymptotic expansion for the wake far downstream from the plate is performed. Remarkably, the perturbation of the flow does not decay with increasing distance from the plate as in a classical wake. The asymptotic solution is implemented as an outflow boundary condition for the numerical solution of the Navier-Stokes equations. The results are compared with a boundary-layer solution obtained in previous work for the limiting case of vanishing Prandtl number.