bluuebunny/crossref_metadata_2025_split huggingface dataset:
Identifying steady and pulsatile two-phase flow regimes with pressure drop signals and acoustic emissions
Authors: Hughes Matthew T , Agarwal Raj M , Garimella Srinivas 
Published: June 2024

Abstract
Identifying two-phase flow regimes is vital for understanding phase-change heat and mass transfer processes. Traditionally, flow regime identification has relied on subjective flow visualization studies, which are then converted to flow regime maps applicable to specific operating conditions. However, these conventional, largely subjective, maps fall short in predicting abrupt changes in flow patterns that often occur during regular operation of vapor compression and absorption heat pumps and other thermal systems. Conventional flow regime maps are also inadequate for addressing the transient, intermittent, or periodic flow regimes that occur in boiling and condensation enhanced using acoustic and other emerging techniques. Therefore, there is a pressing need for alternative flow regime identification techniques that can adapt and reliably track rapid and local changes in two-phase hydrodynamics. Promising candidates for dynamic flow pattern classification include high-resolution pressure drop signals and acoustic emission spectra, which can provide insights into the local hydrodynamics within a flow channel. To assess the feasibility of these measurement techniques, differential pressure and condenser microphone measurements are recorded alongside high-speed videos of a two-phase flow of saturated R134a. The total mass flux and vapor quality are varied to understand the effects of phase velocity and liquid inventory on wave propagation in the channel. Additionally, forced oscillations are introduced to a steady two-phase flow to analyze their impact on flow patterns and their corresponding pressure drop and acoustic signals. Statistical analyses, including Gaussian mixture modeling, are employed to reveal characteristic pressure drop probability associated with each flow pattern, which form the basis for developing a model capable of predicting flow regimes in both steady and oscillating flows. The resulting framework introduces a new flow regime identification technique that can adapt to dynamic operating conditions, benefiting a wide range of thermal systems and phase-change processes.
A checkerboard-free symmetry-preserving conservative method for magnetohydrodynamic flows
Authors: Hopman J A , Trias F X , Rigola J 
Published: June 2024

Abstract
Simulating MHD flows at high Hartmann numbers and low magnetic Reynolds numbers is of high interest for the design of a nuclear fusion breeding blanket, for which high accuracy and conservation of physical properties are of great importance. In this work, a solver is developed that offers these properties through the symmetry-preserving method, while at the same time warranting unconditional stability. Since this method uses predictor values for the pressure and electric potential fields, it can be prone to checkerboarding. Therefore it is extended to include a dynamical checkerboarding solution, which balances this problem with numerical dissipation. This is done through run-time measurements of the intensity of checkerboarding, which is then used as a negative feedback onto the predictor values. The symmetry-preserving discretisation and the dynamical solution to checkerboarding were successfully tested using an magnetohydrodynamic Taylor-Green vortex. The newly introduced method shows results free from numerical dissipation in smooth cases, whereas it avoids checkerboarding in more challenging cases. Finally, the method shows to be unconditionally stable, even on highly distorted meshes.
Modelling of the refrigerant distribution in a critically charged propane heat pump cycle for performance evaluation
Authors: Rogiers Jana , Deblaere Tanya , van Heule Xander , Ameel Bernd , Lecompte Steven , De Paepe Michel 
Published: June 2024

AbstractThe investigation of heat pumps employing natural refrigerants as working fluids has gained substantial momentum, driven by increasingly stringent regulations addressing the global warming potential (GWP) and ozone depletion potential (ODP) of refrigerants. Propane (R290) stands out as an attractive option due to its low GWP and zero ODP. However, a major drawback of propane lies in its flammability. When using propane as working fluid, it will therefore be necessary to limit the total refrigerant charge within the system, without compromising on the heat pump performance. This study endeavors to address this challenge by developing a model of the refrigerant charge distribution in a critically charged heat pump system consisting of an evaporator, a compressor, a condenser, and an expansion valve. In the model, the charge distribution in the two heat exchangers is modelled in detail using a suitable void fraction correlation. For the compressor and expansion valve, a simplified model is employed, in which no refrigerant charge is calculated. Using an iterative procedure, the model can then be used to determine the coefficient of performance (COP), evaporator- and condenser pressure for a heat pump with an established total charge and heat capacity. The influence of different design and operation parameters, such as the degrees of subcooling and superheat, the volume ratio of the evaporator and the condenser, etc., can be assessed.
Experimental investigations of hydrogen iodide (HI) decomposition process for different catalysts and various temperature conditions
Authors: Kowalik P , Bocian P , Jóźwiak P , Badyda K , Hercog J 
Published: June 2024

Abstract
This article presents the results of experimental work carried out at the Institute of Power Engineering on the process of thermal decomposition of hydrogen iodide. This process is one of the three key steps taking place in sulfur-iodine (S-I) thermochemical hydrogen production technology. For this purpose, a laboratory test rig equipped with an electrically heated chemical reactor was constructed, enabling the study of hydrogen iodide decomposition under controlled conditions. The research was carried out using various catalytic substances, as well as different temperature conditions. The process of hydrogen iodide decomposition required keeping the temperature of the reactor above 300°C and continuous analysis of the concentration of hydrogen formed over time. The results of the study will make it possible to determine the kinetics of the hydrogen iodide decomposition reaction under selected conditions of the process, allowing for future optimization of the process with the use of numerical methods.
X-ray computed tomography tracking of the calcium chloride hexahydrate crystallisation process
Authors: Guarda Dario , Martinez-Garcia Jorge , Fenk Benjamin , Gwerder Damian , Stamatiou Anastasia , Worlitschek Jörg , Mancin Simone , Schuetz Philipp 
Published: June 2024

Abstract
The research conducted on phase change materials (PCMs) for latent thermal energy storages (LTESs) is continuously growing in terms of publications, highlighting the importance of this topic. In fact, PCMs present many advantages that could help the energy transition and reduce CO2 emissions, by enhancing the performance of existing systems and better exploiting renewable energy. Therefore, it is of crucial interest to develop new and reliable methods to control LTES. Differently from sensible thermal energy storages, in LTESs the stored thermal energy is not proportional to the temperature. To really have an insight into the level of charge of these storages, it is important to know the liquid fraction, i.e., the amount of the liquid phase with respect to the whole amount of PCM. X-ray computed tomography (XCT) is a technology that allows to non-intrusively “look inside” the materials. In the current study, it was used to analyse the calcium chloride hexahydrate crystallization. This transient process of calcium chloride hexahydrate was tracked with a sequence of XCT scans, one every 6 minutes, resulting in 3D image stacks that were processed to obtain the volumetric liquid fraction evolution over time. Repeatability tests were run to evaluate the reliability of the XCT technique and the volumetric liquid fraction data was used to validate a numerical model developed within ANSYS Fluent framework. XCT offers great opportunities to study the heat and mass transfer mechanisms underlying the main issues of phase change materials, like, for example, supercooling and salt hydrate segregation.
Numerical modelling of heat and mass transfer during cake baking
Authors: Helou Patrick El , Bideau Pascal Le , Fuentes Adrien , Glouannec Patrick 
Published: June 2024

Abstract
This article deals with the development of a numerical multiphysics model to study heat and mass transfer phenomena as well as the swelling during the baking of a cake contained in mold. The aim of this study is to provide an effective numerical tool, experimentally validated, for a better understanding of mechanisms leading to the desired end product. Based on the governing equations for heat and mass transport and under few assumptions (homogenous medium, local thermodynamic equilibrium, ideal gas mixture…), the problem consists in solving a system of five coupled partial derivative equations. Temperature, moisture content, total gas pressure, porosity and displacement are used as state variables in this study. The swelling of dough caused by the increase of total gas pressure is predicted by a viscoelastic model. This thermo-hydro-mechanical model is implemented in finite elements code. Moreover, an experimental laboratory set-up was developed in order to continually acquire temperatures, water losses, deformation and to correctly apprehend the boundaries conditions. The numerical results are then compared with experimental data. They are overall in good agreement. Various operating conditions are tested to check the robustness of predictions.
On the feasibility of overnight industrial high-fidelity simulations of CSP technologies on modern HPC systems
Authors: Alsalti-Baldellou A , Colomer G , Hopman J A , Álvarez-Farré X , Gorobets A , Trias F X , Pérez-Segarra C D , Oliva A 
Published: June 2024

Abstract
In the last decades, computational fluid dynamics (CFD) has become a standard design tool in many fields, such as the automotive, aeronautical, and renewable energy industries. The driving force behind this is the development of numerical techniques in conjunction with the progress of high-performance computing (HPC) systems. However, simulation time remains the most limiting factor for large-eddy simulations (LES) to be adopted in the industry. A consensus exists that, to be feasible, LES simulations should be completed overnight In this context, this work assesses the feasibility of overnight LES simulations on GPU-accelerated supercomputers with TFA, our novel in-house code, which relies on a symmetry-preserving discretisation for unstructured collocated grids that, apart from being virtually free of artificial dissipation, is shown to be unconditionally stable. The study cases will be taken from central receivers used in concentrated solar power (CSP) plants, and a comparison with open-source CFD codes will be made.
Deep residual network for interpolation and inverse problems
Authors: Noorizadegan Amir , Chen Chuin-Shan , Young Der-Liang 
Published: June 2024

Abstract
In this paper, we introduce the Power-Enhancing Residual Network, a simplified version of the highway network. This novel neural network architecture aims to enhance interpolation capabilities. By incorporating power terms in residual elements, this architecture enhances the network’s expressive capacity, leading to new possibilities in deep learning. We explore key design aspects such as network depth, width, and optimization techniques, showcasing its adaptability and performance advantages. Results highlight its precision and demonstrate superiority over conventional networks in accuracy, convergence speed, and computational efficiency. Additionally, we investigate deeper network configurations and apply the architecture to solve the inverse Burgers’ equation, illustrating its effectiveness in real-world problems. Overall, the Power-Enhancing Residual Network represents a versatile and transformative solution, pushing the boundaries of machine learning. The codes implemented are available at: https://github.com/CMMAi/ResNet_for_PINN.
Experiment and model results of a first bidirectional active temperature control module with metal hydrides for a fuel cell
Authors: Lösch H , Fensterle E , Bürger I 
Published: June 2024

Abstract
Many temperature control techniques are based on active heating and passive cooling and thus have a lack of active bidirectional controllability. Whereas, several applications need a precise bidirectional temperature control. The present study demonstrates a novel bidirectional and active temperature control unit (TCU). This unit heats and cools a fluid with the reversible reaction between metals and hydrogen. The reaction of metal hydrides is characterized by a pressure temperature correlation. Hence, the thermal power and the temperature can be regulated by the gas pressure in the TCU. This enables temperature controllers with the pressure as actuating variable on the metal hydride. In this study, an existing LaNi5 reactor is modelled as 0D model. A PID controller is implemented in the simulation and in the experimental setup to stabilize the temperature with the regulation of the pressure in the reactor. Results from experiment and simulation show the stabilization of the temperature.
Computational investigation of the effect of geometry and fuel composition on the performance of a solid oxide fuel cell
Authors: Freitas João , Coelho Pedro J , Ferreira Ana F 
Published: June 2024

Abstract
The need to reduce the consumption of fossil fuels due to their negative impact on the quality of the air and on the greenhouse effect is causing major changes in the energy sector, with a progressively greater contribution of renewable energy sources to satisfy the global energy demand. Fuel cell technology is emerging as a key player in the energy transition since fuel cells convert directly chemical energy to electricity and heat without pollutant emissions. Among the different types available, solid oxide fuel cells (SOFC) can operate at high temperatures (up to 1000ºC), leading to high efficiency and stability. This work is concerned with the computational investigation of a planar solid oxide fuel cell. The governing conservation equations for mass, momentum, energy, species transport and electric charge are solved for a three-dimensional planar fuel cell. Different fuel and oxidizer compositions are considered and their influence on the performance of the fuel cell is investigated. The results show that when the hydrogen molar fraction in the fuel decreases, the maximum power and temperature decrease. The power, the efficiency and the maximum temperature are greater when the oxidizer is oxygen rather than air. The influence of the geometry of the air and fuel channels is also assessed, namely the dimensions of the channels and the effect of steps and obstacles in those channels.
Numerical investigation of different cooling technologies during heatwaves in Catalan Mediterranean buildings
Authors: Garrido Núria , Capdevila Roser , Tontodonati Enrico , Borghero Luca 
Published: June 2024

Abstract
The Mediterranean area is particularly affected by heatwaves, which are extremely critical for health and productivity of people inside the dwellings as well as for energy consumptions related to cooling demand. This study numerically investigated the resilience of different cooling technologies in the most common construction in Catalan building stock during present and future climatic conditions, heatwaves. The studied technologies include green roof, blinds, advanced windows, air conditioning and their combinations. Meteorological data of heatwaves for Barcelona city have been created for three time periods, Present, Mid Future and Long Future. They have been modelled using dynamical downscaled Regional Climate Models, climate projections based on IPCC scenarios. Resilience was assessed using indicators that consider the linear correlation between the grade of overheating inside a dwelling and the severity of outdoor conditions. Thermal comfort and survivability have been also investigated, evaluating sensations of building’s occupants related to indoor air temperature and relative humidity. The original building presented acceptable levels of resilience with a resilience index α below 1, while thermal comfort conditions resulted poor, especially during heatwaves, being for more than 60% of the time in Extreme Caution conditions or worst. The application of the different cooling technologies significantly helped in the improvement of resilience and survivability inside the dwelling. However, their performances reduced in the future scenarios, reaching more than 90% of the time under Extreme Caution conditions or worst. Air conditioning resulted the best solution for avoiding overheating, especially in heatwaves constraining it to a maximum of 1.8°C. Combinations of several passive measures resulted necessary for maintaining suitable conditions.
Comparative analysis of the behaviour of the hot water production system of an indoor swimming pool
Authors: Velasco F.J.S. , Giménez-Villa J. , García-Cascales J.R. , Illán-Gómez F. , Delgado Marín J.P. , Otón-Martínez R.A. 
Published: June 2024

Abstract
In this paper, we analyse the thermal behaviour and the environmental impact of an indoor swimming pool placed in Pozo Estrecho, Cartagena, in the Southeast of Spain. The existing installation is formed by a group of solar thermal collectors supported by two propane heaters which heat the water of the pool and satisfy the needs of hot water in the changing room of the pool. Here we propose an installation based on the use of a heat pump supported by solar thermal collectors. In this work, we first describe the installations. They are modelled with Trnsys and the models employed briefly described. Later, we compare their primary energy consumption and its environmental impact in terms of their CO2 emissions. A rough estimate of its economic impact is also given. Some conclusions are finally drawn.
Enhancing thermal modelling of electric machines: steady-state verification of a novel methodology
Authors: Nonneman Jasper , T’Jollyn Ilya , De Paepe Michel 
Published: June 2024

Abstract
The increasing power density of electric machines for electric vehicles necessitates accurate thermal analysis in design through simulations with computation times not exceeding one minute. Existing thermal models are either accurate and complex while requiring large computation times or they are fast but lack accuracy. To address these challenges, a novel hybrid modelling methodology is proposed, combining 3D lumped parameter thermal networks with thermal resistances extracted from 2D finite element models (FEM) to reduce computation demands while preserving accuracy. Verification of the modelling methodology against 3D FEM in OpenFOAM shows key component temperature deviations of less than 0.67 °C comparable to the 3D FEM uncertainty of 0.39 °C. The computation time is 18.3 s compared to 44 h for 3D FEM. This highlights the time-efficiency of the proposed methodology while maintaining accuracy for key component temperatures.
Low enthalpy geothermal source for sustainable energy production in small islands: a real case study
Authors: Fraia Simona Di , Massarotti Nicola , Vanoli Laura 
Published: June 2024

Abstract
The global demand for clean and sustainable energy sources has significantly increased in recent years, mainly because of concerns about climate change and the finite nature of traditional fossil fuel reserves. In this context, geothermal energy has gained significant attention as a reliable and eco-friendly alternative. In particular, low enthalpy geothermal resources have emerged as an attractive option due to their accessibility, widespread distribution, and potential for decentralization. Moreover, reliability and flexibility of this source allow for year-round utilization to meet diverse energy demands, resulting in reduced dependency on traditional energy sources and associated greenhouse gas emissions. For this reason, geothermal energy appears to be a promising solution in small islands, where energy production is often a challenge due to the absence of infrastructures that make them energy-dependent on the mainland. Therefore, in this work, low enthalpy geothermal source is considered as effective and sustainable solution for electrical energy production in small islands. As case study a low temperature source available in Ischia island, Southern Italy, is considered. The proposed solution is analysed from energy, economic and environmental point of view.
Experimental investigation of the impact of surface tension and artificial nucleation site geometry on the bubble growth
Authors: Vodopivec M , Berhe MG , Bucci M , Zupančič M , Fontanarosa D , Može M , Castagne S , Golobič I , Vetrano MR 
Published: June 2024

Abstract
The present work provides an experimental assessment of the impact of liquid surface tension on the single bubble dynamics generated by artificial nucleation cavities during boiling in a quiescent liquid. De-ionized water is used with and without added non-ionic surfactant (Dynol 800) to modify the fluid’s surface tension while keeping the other thermo-physical fluid properties unchanged. Furthermore, two different cavity geometries are investigated: a vertical and a 30°-inclined cone produced via femtosecond laser texturing. This paper shows preliminary results related to the influence of surface tension and cavity geometry on the single bubble dynamics. A methodological baseline is provided to enable future studies aiming to answer still-open questions about vapour bubble nucleation phenomena.
Direct Numerical Simulation of single bubble dynamics in nucleate pool boiling with micro-region modeling and thermal coupling to a solid wall
Authors: Wei Linkai , Bois Guillaume , Nikolayev Vadim S. 
Published: June 2024

Abstract
In this study, we conduct two-dimensional, axisymmetric simulations to investigate the growth and departure of a single bubble, with a particular focus on the conjugate heat transfer between the fluid and the heating wall. A multiscale modeling approach is employed to account for nanoscale effects near the liquid-vapor-solid triple contact line (CL). At the macro (bubble size) scale, the interface dynamics is captured with the front-tracking method by using the open-source code TRUST/TrioCFD. The macro scale algorithm is coupled with a sub-grid micro-region model. It is driven by the wall superheating at the CL as input, and predicts the macroscopic apparent contact angle and heat fluxes. To validate our modeling approach, we first conduct quantitative comparisons using the data on the bubble growth experiment RUBI and its simulations. Next, an investigation of the case of water under atmospheric pressure and gravity is performed. Notably, we observe a significant spatial variation in temperature near the nucleation site during the expansion and contraction of the bubble base. This variation greatly affects the thermal boundary layers in the fluid and solid domains and the bubble growth, demonstrating the need to resolve the conjugate heat transfer in the considered cases.