bluuebunny/crossref_metadata_2025 huggingface dataset:
Research on Simulation Technology of Excitation Response of Aircraft Structural Based on Finite Element Model in Flutter Flight Test
Authors: Ming Lei
Published: June 2024

To simulate excitation response of the aircraft structural of flutter test aircraft under different excitation methods. A simulation method for excitation response of flutter flight tests based on finite element models has been proposed. This method is based on the finite element model of the aircraft structure. Establish aerodynamic and excitation force models for flutter flight tests. Obtain a simulation model for the excitation response of aircraft flutter flight tests. Solve the model and simulate various excitation methods for flutter flight tests. Firstly, a detailed introduction was given to the excitation modeling method for aircraft flutter flight tests, including two excitation models: external excitation and control surface excitation. Then, the finite element model of the structural dynamics of a single wing with ailerons is taken as the research object. Establish a single wing flutter flight test excitation response model. Implemented simulation of control surface sweep excitation, control surface pulse excitation, and small rocket excitation. The feasibility of this method has been verified. Finally, based on the finite element model of the entire aircraft, a flutter flight test excitation response simulation model was established. We have conducted analysis and research on sensor position optimization, excitation method optimization, excitation response amplitude prediction, and flutter boundary prediction. And the simulation optimization analysis results were compared with the flight test results. Analyzed the promoting effect of flutter flight test excitation response simulation on flight tests.
Honeycomb Elastic Metasurfaces for Broadband Control of Flexural Waves
Authors: Cheng Jiali , Li Bing
Published: June 2024

Elastic metasurfaces are artificial planar structures endowed with unique properties that natural materials do not possess. They exhibit significant potential in the realm of wave control. Despite the widespread attention garnered by metasurfaces due to their ultrathin profile, ease of design and fabrication, and enhanced physical characteristics, they still grapple with the challenge posed by their narrow operational bandwidth. In this study, a structurally compact, subwavelength-scale honeycomb metasurface is proposed for broadband manipulation of flexural waves. Through modulation of the unit cell dimensions, precise control over the phase is achieved, enabling a series of remarkable wavefront manipulations, including anomalous refraction, energy concentration, self-bending beam, and source illusion. Results indicate that compared to conventional localized resonance metasurfaces, the introduced approach offers advantages in terms of broad bandwidth, compactness, and high efficiency. This endeavor holds the potential to provide more comprehensive methods for vibration attenuation, noise reduction, and wave control.
Modulation of flow, heat, and mass transfer in turbulent double-diffusive convection
Authors: Kenjereš S. , Roovers R.
Published: June 2024

The present study addresses numerical simulations of the double-diffusive convection in a turbulent regime. The characteristic concentration and temperature Prandtl numbers (PrC
= 700 and PrT
= 7) correspond to the typical seawater properties. Here, we applied the Large-Eddy Simulation (LES) approach, with relatively simple subgrid turbulence closures of momentum, concentration, and temperature for the unresolved scales. The wall-resolved LES approach proved to work well on significantly coarser numerical mesh than used in recent Direct Numerical Simulation (DNS) studies of Yang et al. (2016) in the intermediate range of working parameters, 107 ≤ RaC
≤ 109, 0 ≤ RaT
≤ 106, which covers the quasi-Rayleigh-Bénard, fingering, and damping flow regimes. A good agreement between concentration and temperature Nusselt numbers is obtained. The instantaneous Nusselt numbers distribution revealed a significant impact of the imposed strong thermal stratification (RaT
= 106) in comparison to the neutral case (RaT
= 0).
Stagnation point heat transfer under a free-surface jet
Authors: Harnik R S , Haustein H D
Published: June 2024

Laminar free-surface jet impingement is a crucial configuration for heat transfer processes. Focusing on the link between stagnation-point heat transfer and near-axis radial acceleration, its dependence on jet width and profile is studied. Thus, heat transfer depends on: fluid properties, flow rate, nozzle length, nozzle-to-plate spacing, surface tension and gravity (Pr, Re, L/d, H/d, We & Fr, accordingly). As existing theory is limited to specific cases, a new general description is developed from analogy to submerged jets. Validated by two-phase flow simulations, this description captures key jet dynamics evolution (centerline velocity, profile curvature). It reveals significant property changes during jet flight due to relaxation (L dependence) and contraction (Re/Fr dependence). Unlike submerged jets, contraction raises arrival Reynolds number, leading to additional dependencies Nu ∝ L and Nu ∝ H/Fr, and further deviations at low-We and -Re. The theory successfully predicts heat transfer across diverse conditions and converges to negligible gravity (horizontal jet) as expected.
Comparison between DNS and RANS approaches for liquid metal flows around a square rod bundle
Authors: Trane D , Grespan M , Angeli D
Published: June 2024

The thermal-hydraulic characteristics of liquid metal flows around rod bundles are of great interest for the research and design of fourth generation nuclear reactors. Currently, a large research effort is aimed at the development of accurate numerical models for low Prandtl number fluid flows, since the data available in the literature are quite scarce. Direct Numerical Simulation (DNS) is undoubtedly the most accurate approach, but its large requirements of computational resources and time make it less practical than other simplified methods such as the Reynolds-Average Navier Stokes (RANS) approach. The present paper provides a comparison between numerical results of a flow of liquid Lead-Bismuth Eutectic (LBE) at Pr=0.031 around four vertical cylindrical rods arranged in a square lattice, obtained by DNS and RANS. Several turbulence models are considered, including the standard k−ε, k−ω SST, and two Reynolds stress models, namely the ones by Launder, Reece and Rodi (LRR), and Speziale, Sarkar and Gatski (SSG). The accuracy of these models is assessed by comparing the mean Nusselt number, the pressure drop, and local field distributions with those obtained by DNS.
Structured illumination with infrared imaging for measuring thermal conductivity
Authors: Bhat Ashwath , Dames Chris
Published: June 2024

With developments in advanced manufacturing and materials by design comes the need for high-throughput thermal characterization and inspection. Towards this end, Structured Illumination with Thermal Imaging (SITI) is an all-optical pump-probe thermal characterization technique recently developed by our group. In the first generation [Zheng et al., Appl. Phys. Rev. 9, 021411 (2022)] SITI uses an LED with a digital micromirror device (DMD) to “structurally illuminate” and heat the sample with dynamic patterns, a visible light camera for thermoreflectance based “thermal imaging” [leveraging a Microsanj MTIR120], and the resultant temperature response was fit with a thermal model to characterize the sample’s thermal properties. This represents a novel approach to dynamic and flexible spatial mapping of thermal properties by virtue of being a non-contact technique and having a simpler scanning means (computer control only) than conventional pump-probe laser methods. SITI also can tolerate rough samples with diffuse reflections. This talk presents the second generation of SITI. The pumping is now based on a lower cost off-the-shelf digital projector. The thermometry is now performed using an infrared (IR) camera, which we find is a more flexible and accessible hardware approach compared to the thermoreflectance microscopy used previously. With these updates the setup can deliver higher heating power and a broader range of frequencies, allowing an extended range of samples that can be studied. We have demonstrated SITI’s ability to measure the thermal conductivity of a microscope glass slide.
LES investigations of turbulent heat transfer structures with exponential power escalation
Authors: Roumet Elie , Nop Raksmy , Dorville Nicolas , Duluc Marie-Christine
Published: June 2024

The BORAX-type accident is a key scenario in the safety design of pool-type experimental nuclear reactors. It considers a reactivity insertion large enough to initiate an exponential power escalation with a period as small as tens of milliseconds, necessitating effective heat removal by the coolant system. This study presents a computational analysis of single-phase transient heat transfer under thermal-hydraulic conditions relevant to such reactors, focusing on turbulent channel flow between planar fuel plates with highly subcooled water. Our investigation uses Large Eddy Simulation (LES) performed with TrioCFD, the open-source CFD code developed by the French Atomic Energy Commission (CEA). Several modeling options are tested: incompressible flow with temperature as a passive scalar, incompressible flow with varying viscosity, and quasicompressible flow with temperature-dependent viscosity and mass density. To evaluate the accuracy of our physical models, all simulations were performed under uniform conditions, using the same experimental parameters, mesh, and numerical strategies. The specific examined scenario involves a highly subcooled turbulent channel flow at moderate pressure, experiencing an exponential power increase. We ensure detailed turbulence resolution at the Batchelor scale in the wall normal direction close to the heating wall. This communication presents a comparative study of LES simulations of the single-phase flow under exponential power excursion at the wall. Subsequent analyses focused on the impact of different velocity-temperature couplings on the prediction of wall heat transfer, incorporating comparisons with experimental infrared thermometry measurements. Early in the transient phase, temperature peaks are confined within turbulent streaks, as reported in the existing literature. However, as the exponential power transient unfolds, the viscous layer and streak structures destabilize, leading to a more dispersed distribution of hot spots. Preliminary findings suggest a transition in heat transfer modes from turbulence-driven to conduction during the final stages of the single-phase transient.
The influence of cold plate height on thermal management of a liquid-cooled battery pack
Authors: Birinci S , Albayrak M , Saglam M , Sarper B , Aydin O
Published: June 2024

This study focuses on the numerical investigation of the cooling efficiency of a cold plate with different heights for a Li-ion battery pack. The battery pack is arranged in a 2×18 configuration and consists of cylindrical 18650 cells. A new cold plate design is presented for this purpose, and the thermal performance of the system is evaluated under various operating scenarios. Five-volume flow rates (0.1-1.0 l/min) and four distinct cold plate heights (30-40-50-60 mm) are investigated for the 2C discharge rate using ANSYS Fluent software. The study investigates several configurations to establish the maximum temperature difference within the BP, maximum temperature of the BP, pressure drop, and cooling efficiency. As a result of the simulations the ideal flow rate is founded within the range of 0.5-0.75 l/min and a cold plate height of 50 mm is selected as the most favorable design configuration.
Optimum geometry of some heat exchangers
Authors: Karvinen R
Published: June 2024

Heat exchangers are present in our daily living and industrial applications. The size scale of heat exchangers is very large ranging from very small chips in electronics to huge equipment in process and energy industry. In the paper optimization approaches of some industrial examples are given. The goal is to present how analytical results can and must be used in multi-objective optimization of applications. The details of equations are not given due to page limits but they are found in the literature. The main goal is to show how numerical, analytical and optimization methods can be and must be combined in optimization of exchanger design and performance. The performance depends on very many factors and contradictory requirements must take into account such as maximization of heat transfer and simultaneously minimize for example the weight and size. Modifications of four existing applications are component placement on a wiring board, optimization of heat sink in power electronics, quality control in a glass tempering and optimization of a very huge heat exchanger called economizer in a recovery boiler.
Thermal performance against gravity of an AlSi10 AM heat pipe with a diamond lattice structure
Authors: Vitali L , Menini S , Guilizzoni M , Niro A
Published: June 2024

Metal Additive Manufacturing has gained momentum as a viable production technique for specialized heat transfer devices, in particular for industrial sectors characterized by small production numbers associated with high-performance requirements. Within the space industry, ESA is leading and funding several applied research programs to explore the possibility to employ AM for building electronic boxes with embedded heat pipes, in order to reduce manufacturing post-processing steps and contact thermal resistances. In the context of tender 1-10238, the project “Heat Pipe Solutions for High Power Systems” (HPS2) has developed and tested lattice-based heat pipes, that are intended to be integrated in electronic modules. In this paper, the heat transfer performances as function of input power and tilt angle against gravity of a 150 mm long heat pipe with a 20 mm evaporator section and a 40 mm condenser section are presented and compared with the results of the models of performance limits, based on the measured properties of the lattice.
Experimental and numerical convective heat transfer performance analysis of a confined impinging round jet with triangular tabs under crossflow influence
Authors: Saglam M , Birinci S , Sarper B , Aydin O
Published: June 2024

In this study convective heat transfer performance of a confined impinging round jet with/without nozzle tabs under channel crossflow is investigated experimentally and numerically for a wall mounted heated module. Numerical investigations are carried out for different jet to crossflow velocity ratios (Vr) and compared to experimental data. Four different Vr values (5,6,8, and 10) are tested for single target plate distance to jet nozzle diameter ratio (H/D=8). ANSYS Fluent software is used for numerical simulations while infrared thermography is utilized for experimental investigations. Surface temperature values of the wall mounted module are obtained and presented along with complex flow structures obtained via numerical simulations. Results show that crossflow has decisive effect on temperature distribution on the component. By inserting triangular tabs to the nozzle exit, it is possible to further decrease the surface temperature of the module and minimize the crossflow caused jet deflection. The addition of triangular tabs resulted in a significant increase of up to 10% in the mean Nusselt number on the top surface of the module at Vr=10.
Design and numerical simulation of a 45 kWel multi-source high-flux solar simulator as a heating source of dielectric materials positioned in a microwave characterization cavity
Authors: Touoyem Talla J A , Henriot B , Duvaut T , Tantot O , Delhote N , Charles M , Randrianalisoa J
Published: June 2024

This study reports the design and modelling of a high-flux solar simulator (HFSS) combined to a resonant cavity for microwave dielectric properties characterization of ceramics at very high temperatures. The HFSS comprises seven xenon arc lamps with ellipsoidal reflectors, delivering a maximal electrical power of 6.5 kWel each. Positioned on a virtual sphere of around 1600 mm radius, the lamps provide concentrated irradiation heating on a sample positioned inside the resonant cavity. The propagation of the lamp’s irradiation to the sample and the cavity is simulated using Monte Carlo ray tracing method. An ANSYS Fluent finite volume method for solving the resulting multimode heat transfer and flow indicate a radiative flux reaching 1.84 MW m−2, and a sample temperature of approximately 1470°C with 10 % non-uniformity. These results suggest that the designed heating system and resonant cavity is suitable for conducting microwave dielectric properties characterization of refracting ceramic materials at high temperatures, addressing a gap in studies focusing on temperatures exceeding 1000°C.
Effect of using an ionic liquid as additive in water/LiBr mixture in a horizontal falling film absorber
Authors: Tariq Hussain Ahmed , Bourouis Mahmoud , Coronas Alberto
Published: June 2024

Absorption Heat Pumps (AHPs) are attractive technology for space cooling from low grade energy resources. This technology is of special interest when water/LiBr is used as a working mixture, as water is a natural, non-toxic and cost-effective refrigerant without any contribution to global warming. Nonetheless, water/LiBr AHPs do come with certain inbuilt issues as LiBr tends to crystallize at higher concentrations, that hinder the technology from functioning as an air-cooled system and in a reversible mode for space heating. Addition of Ionic Liquids (ILs) as additive is therefore important which improves the solubility of LiBr in water/LiBr solution. The addition of IL as additive is 1,3-Dimethyl-1H-imidazolium chloride [DMIM][Cl] which is 6% of absorbent (LiBr+IL) by mass. This paper aims to compare the heat and mass transfer involved in water absorption process of water/LiBr and water/(LiBr+[DMIM][Cl]) mixtures in a horizontal tubes falling film absorber.
Particle dispersion produced by a turbulent free convection flow in a room-sized cubical cavity
Authors: Pallares Jordi , Lavrinenko Akim , Marchioli Cristian , Cito Salvatore , Fabregat Alexandre
Published: June 2024

This paper introduces the framework for the ongoing “2024 International CFD Challenge on the Long-Range Indoor Dispersion of Pathogen-Laden Aerosols.” The Challenge is designed as a blind test to assess the accuracy of computationally efficient turbulence modeling techniques, including URANS and LES, in replicating both the hydrodynamics and aerosol dispersion in an idealized indoor environment. To evaluate the simulations, DNS data of turbulent natural flow at a high Rayleigh number within a room-sized enclosure will serve as a reference benchmark. Participants have the flexibility to conduct simulations of the same flow configuration using their preferred CFD software, employing URANS, LES, and/or hybrid methods. The Challenge was officially launched on October 16, 2023, and has garnered participation from 31 teams representing 18 different countries, with the expected submission of results in May 2024. The outcomes of the comparison between the different modelling approaches and the reference DNS will be presented and discussed during the conference.
Numerical simulations of bubbly turbulent convection in cubical geometries
Authors: Marichal J , Ruyer P , Bartosiewicz Y
Published: June 2024

In this work we present numerical results of pool boiling flow in a turbulent Rayleigh-Bénard convection configuration, using our in-house code in a cubical geometry. The problem in hand is encountered in various natural phenomena as well as in industrial applications. An Eulerian-Lagrangian approach is developed for the mixture of liquid water and vapor bubbles. The liquid mean temperature is close to the saturation temperature and is governed by the quasi-incompressible Navier-Stokes equations that are solved using DNS standards. The motion and growth/shrinkage of each individual vapor bubble is modeled and the backward effect of the bubbles on the fluid is accounted via momentum and energy exchanges between the two phases (two-way coupling), as well as variations in fluid phases volumetric fractions (volumetric coupling). In such pool configuration the non-dimensional parameters governing the flow are both those relative to Rayleigh-Bénard convection, namely Rayleigh number, Prandtl number and aspect ratio, and those to boiling, namely the overall vapor volumetric fraction, the bubble size based Reynolds number, the degree of superheat of the liquid scaled by the overall temperature difference, and the Jakob number (sensible heat to latent heat ratio).

At first, we describe the model used and its corresponding validation, involving natural convection, isolated bubble dynamics and coupling between bubbly and bulk flows. In the second part, we consider the study of the relationship between heat transfer through the pool (Nusselt number) and the flow topology for different settings of the bubbly configurations.
Approximate analytical solution for solidification of PCM in cylindrical geometry with temperature‑dependent thermal conductivity-perturbation method
Authors: Jamal-Abad Milad Tajik , Cortés Cristóbal , Ranz Javier Pallarés , Gil Antonia
Published: June 2024

The Solidification process of Phase change materials inside cylindrical enclosures is analyzed and analytical solutions are derived to determine the positions of the interfaces at different time intervals. In this current investigation, we address the scenario involving temperature-dependent thermal conductivity. For the first time, we employ perturbation techniques to analytically derive the dimensional temperature for both phases. Our study specifically incorporates a linear model to account for the variation in thermal conductivity with temperature. The results show that the duration of complete solidification relies on the Stefan number. As these parameter is augmented, the total solidification time of the cylinder diminishes and escalates, respectively. Furthermore, it has been observed that an augmentation in the thermal conductivity of the phase change material (PCM) leads to a swifter solidification process.
Numerical simulations of temperature loads on multilayer Laue lenses
Authors: Rek Z , Chapman H N , Bajt S , Šarler B
Published: June 2024

We present numerical simulations of the heat loads on novel diffractive X-ray optics, known as multilayer Laue lenses, exposed to high-intensity X-ray beams produced by an X-ray free electron laser (XFEL). These lenses can be used to focus XFEL beams to nanometer spots. The temperature distribution within the lens and temperature evolution as a function of incident pulse frequencies were calculated for two different lens geometries and several material pairs and material ratios of the MLLs. Simulations considered the special pulse structure of European XFEL with X-rays being delivered in pulse trains. After defining the geometric model, computational grid, material properties, and boundary conditions, a grid sensitivity study was carried out. We solved the transient heat energy transport equation in solids for mixed boundary conditions. The results of these simulations will help select materials and lens geometry for future XFEL experiments.
Estimation of thermophysical properties of a pouch-type Li-ion battery using an inverse methodology
Authors: J Jithu , Vasista Kasavajhula Naga , Kumar Suraj , Srinivasan Balaji , Balaji C.
Published: June 2024

The growing popularity of electric vehicles highlights the crucial role of batteries. Effective battery thermal management is crucial for improving performance, reliability, and safety, especially in tropical areas where overheating is a key challenge. This necessitates a comprehensive understanding of the thermophysical properties of batteries. The present study concerns the estimation of the temperature-dependent orthotropic thermophysical properties (kx
, ky
, kz
, cp
) of the active material in a pouch-type Li-ion battery using an inverse methodology. An experimental study is conducted on a commercial AMP20M1HD-A Li-ion battery to measure the surface temperature at various locations using thermocouples. The forward model consists of the three-dimensional unsteady conduction problem and is solved in COMSOL using experimental boundary conditions. The data generated is used to train an Artificial Neural Network, which acts as a replacement for the forward model. The Metropolis Hasting-Markov Chain Monte Carlo algorithm along with the Bayesian inference inverse model is used for analyzing the posterior distribution and the average estimates for thermophysical properties are obtained. The temperature dependence study shows a significant correlation between temperature and battery thermophysical properties. The accuracy of the employed inverse model is validated by obtaining the surface temperature using the estimated thermophysical properties and comparing it with the measured surface temperature.
Calibration and verification of CFD-VOF models for the analysis of pressurization scenarios in LH2 tanks
Authors: Schillaci Eugenio , Amani Ahmad , Oliet Carles , Rigola Joaquim , Castro Jesus
Published: June 2024

Due to its high power density, the aviation sector is pushing towards its electrification by designing new propulsion systems based on cryogenic liquid hydrogen (LH2). From an engineering point of view, the efficient design of tanks constitutes one of the main challenges. They must guarantee efficient isolation of the hydrogen to avoid its evaporation and, at the same time, ensure reasonable weight and dimensions. Using numerical simulations is fundamental for studying heat transfer between the external environment and the liquid fuel. This work focuses on the simulation of multiphase liquid-gas flow to analyze the tank pressurization as a function of different external heat fluxes. A commercial CFD software is used to perform simulations. VOF simulations with the Lee mass transfer model are employed, and some critical numerical parameters are analyzed to provide information on the optimal values.
Enhancing thermal management in cylindrical Li-ion battery through PCM integration with variable contact area
Authors: Shrinet Ekta Singh , Kumar Lalit
Published: June 2024

Cylindrical Li-ion batteries are widely embraced in various sectors, notably electric vehicles and renewable energy storage systems. An effective thermal management system is vital for their safe and dependable operation, enhancing both the performance and reliability of the system. This study employs a distinctive hybrid cooling strategy consisting of a phase change material (PCM) at the centre of the battery and liquid cooling at the surface of the cylindrical batteries. The contact area between the coolant and the battery’s surfaces varies to make sure same heat transfers from each battery. This approach is instrumental in maintaining thermal uniformity and regulating the maximum temperature. In the numerical analysis, we employed ANSYS Fluent 2022 R1 to create the computational model encompassing the Li-ion battery, PCM, and liquid cooling system. This arrangement utilized eight 18650Li-ion batteries, with each battery housing a 2 mm radius PCM rod at the centre of the batteries. A heat-conducting element (HCE) was introduced to facilitate contact between the battery and the coolant channel. Water was selected as the coolant, and the coolant channel cross-sectional area is 65 × 2 mm2. The relationship governing the variable contact area is determined by fixing the velocity and the first battery contact area. The variable contact geometry maintains thermal uniformity throughout the battery module, resulting in a 74% enhancement in thermal uniformity. Nevertheless, the integration of PCM inside the battery effectively prevents individual batteries from surpassing specified temperature limits. It yields a remarkable 36.64% enhancement in thermal uniformity compared to situations in which PCM is not present, albeit with a 3.75% capacity loss. Furthermore, the study investigates the effects of coolant flow rates and performs an extensive analysis of temperature variation and melting fraction.
Thermal performance of a chaotic heat exchanger: an experimental study
Authors: Hani Nouhaila El , Lacassagne Tom , Hamidouche Souria , Bihan Loic Le , Bontemps André , Amir Bahrani S.
Published: June 2024

Improving the efficiency of heat exchangers requires innovative approaches that reconcile performance and sustainability. This study examines the potential of a curved geometry employing chaotic advection as a passive technique for improving internal heat transfer. The Chaotic Heat Exchanger (CHE) studied was constructed using 18 bends at 90 degree angles, and by simply turning each bend at a 90-degree angle to the previous one. The aim is to investigate the chaotic heat exchanger by focusing on heat transfer efficiency. A comparative analysis is carried out between the chaotic heat exchanger and a conventional Helical Heat Exchanger (HHE), using an experimental approach with water as the internal hot fluid. The Reynolds number examined ranges from 250 to 3500. It is found that the CHE outperforms the HHE both in terms of heating capacity and of inner Nusselt number, particularly in the intermediate Reynolds number range.
Numerical insights into turbulent penetrative convection over localized heat sources
Authors: Kenjereš S , Žilić A , Hanjalić K
Published: June 2024

The turbulent penetrative convection into a stable convective boundary layer represents an important phenomenon in environmental engineering and atmospheric science. In the present study, we present a series of numerical simulations performed by two modeling approaches: the high-fidelity Large-Eddy Simulations (LES), and the less computationally demanding transient Reynolds-Averaged Approach (TRANS), but with an advanced sub-scale turbulent heat flux model. By simulating different localized heat sources over the ground, and by performing a direct comparative assessment of results obtained by LES and TRANS, we confirmed an overall good agreement in predicting the time evolution of the horizontally averaged temperature profiles. Similarly, the morphology of instantaneous thermal plumes and large convective structures predicted by TRANS were in reasonable agreement with the referent LES predictions.
Unstructured Conservative Level-Set (UCLS) method for reactive mass transfer in bubble swarms at high density ratio
Authors: Balcázar-Arciniega N , Rigola J , Oliva A
Published: June 2024

This research presents a parallel Unstructured Conservative Level-Set (UCLS) method for reactive mass transfer in bubbles with a high-density ratio. This method uses the multiple-marker UCLS approach to circumvent the numerical coalescence of bubbles, combined with the finite-volume method to discretize transport equations on 3D collocated unstructured meshes. The fractional-step projection method solves the pressure-velocity coupling. The central difference scheme discretizes the diffusive term, whereas convective term within the momentum transport equation, level-set advection equations, and mass transfer equation are discretized by unstructured flux-limiters schemes. Such a combination of numerical techniques preserves the numerical stability in bubbly flows with a high Reynolds number and high-density ratio. Numerical and physical findings on the effect of physical properties ratios on the reactive mass transfer are reported, including their effect on the Reynolds number, interfacial area and Sherwood number.
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

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

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

The 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

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

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

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

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

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

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

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.