bluuebunny/crossref_metadata_2025 huggingface dataset:
Application of a Modal Parameter Identification Method Based on Variational Mode Decomposition in Flight Flutter Testing
Authors: Wang Shaonan
Published: June 2024

Signals of flight flutter testing exhibit non-stationary characteristics, closely spaced modes, and low signal-to-noise ratio, presenting challenges in data processing. In recent years, the variational mode decomposition (VMD) method has emerged as a promising approach to mitigate mode mixing and exhibit robust noise resistance. Therefore, a novel time-frequency domain modal parameter identification method based on VMD is proposed to process impulse response signals in flight flutter testing. The modal frequency and damping ratio are determined through a three-step process: VMD analysis, Hilbert transform, and least square fitting. The efficacy of the proposed method in identifying closely spaced modes and resisting noise is validated through a numerical example. Furthermore, this method is applied to analyze two types of pulse excitation signals in actual flight flutter testing: one induced by the pilot’s shaking stick and the other induced by small rocket excitation. The obtained modal parameters are compared with those from ground vibration tests and specialized software, respectively, to showcase the effectiveness and superiority of the proposed method.
Vibration signals reconstruction with diffusion model for bearing fault diagnosis
Authors: Gu Zeyu , Ma Jianwei
Published: June 2024

Rotating bearing plays an important role in many mechanical equipment operation, such as satellite in orbit. There are in urgent need of constructing effective prognosis and diagnosis system oriented rotating bearing. Traditional bearing fault diagnosis methods enhance fault feature with sparsity-assisted prior, which are not suitable for complex vibration signals. Meanwhile, it is difficult to extract fault feature from under-sampled vibration signals. In this paper, we firstly utilize generation diffusion model to learn probability distribution of bearing fault data. As a deep generation prior, we combine the diffusion model and reconstruction problem with regularization term. The unsupervised learning method is not restricted to specific measurement matrix. The experiment in Machinery Failure Prevention Technology (MFPT) Dataset verifies the effectiveness of our algorithm. Compared with the sparse model (L1-norm) and hierarchical hyper-Laplacian prior induced model (HHLP), our method achieves better reconstruction signal to noise ratio (SNR) performance and maintains the fault frequency information from different under-sampled data.
Study On Microvibration Test Technology For Satellite Multistage Unloading
Authors: Yao Wu , Chuang Liu , Gang Sun , Hao Sun , Qi Xin , Yicun Xie , Chunliu Zhang
Published: June 2024

In this paper, the structural forms of high-precision satellites are analyzed, and the new changes of boundary condition simulation when carrying out ground microvibration tests are discussed. Combined with the new requirements, the multi-stage unloading micro-vibration test method is studied, and the multi-stage unloading micro-vibration test system is designed, which lays a foundation for the follow-up micro-vibration test of a new generation of satellites.
A Decentralized Consistent Approach for Multi-Robot Simultaneous Localization and Object Tracking
Authors: Wang Xuedong , Huang Yingtao , Lu Xinyuan
Published: June 2024

This study focuses on the problem of multi-robot simultaneous localization and object tracking (MR-SLOT), which involves the collaborative effort of multiple mobile robots tracking a moving object on a plain. To address this challenge, this paper introduces a fully decentralized approach based on the extended Kalman filter and covariance intersection (CI), denoted as CI-SLOT. In the proposed approach, each robot can precisely track the robot-to-object correlations. Moreover information exchange occurs solely among one-hop communicating robots, and each robot only maintains the latest estimate of the object and its pose. The simulation results have shown that the performances of CI-SLOT are better than those of the state-of-the-art approaches of comparable processing and communication costs.
Orbit Determination of High Orbit Spacecraft based on BDS-3 using Extended Kalman Filter
Authors: Ma Xiangtai , Hu Yanfeng , Yu Miao , Dong Xurong , Lai Jiangfeng
Published: June 2024

The positioning of highly elliptical orbit (HEO) spacecraft is very important in deep space exploration and other missions. The Beidou Navigation Satellite System (BDS-3), which was completed in 2020, has put forward new ideas for using GNSS technology to make up for the lack of earth-based TT&C systems. At the same time, the selection of the gravity field order and the perturbation forces must be considered when using dynamical methods for HEO spacecraft positioning. In this paper, simulation experiments are carried out based on the Two-Line Orbital Element (TLE) data of BDS. Two HEO satellites with different semimajor-axis (67509.6 km, 212857.3 km) are selected as the target spacecraft orbits. The single point positioning (SPP) method and Extended Kalman Filter (EKF) method are used for HEO spacecrafts positioning respectively. The experiments show that a 20×20 order gravity field model can be chosen for the orbital integral of HEO spacecraft orbits, and the integration error caused by solar gravity and lunar gravity should be taken into account with the change of orbital altitude. Adding Geostationary Orbit (GEO) and Inclined GeoSynchronous Orbit (IGSO) navigation satellites improved the visibility of these two orbits by 19.45% and 16.64%, respectively, and improved the GDOP value by 14.1% and 3.8%, respectively, compared to observing MEO satellites only. The use of the EKF method can effectively improve the positioning accuracy of the HEO spacecraft compared to the SPP method. For the spacecraft in HEO-1, the RMS value of the positioning errors of the EKF method was 67.82 m, and the accuracy of each direction was improved by 44.28%, 38.85%, and 38.62%, respectively. For the spacecraft in HEO-2, the positioning errors in the x direction of EKF method was within 12 km and within 2 km in the y and z directions. The accuracy of these three directions was improved by 84.91%, 79.24%, and 58.64%, respectively.
Incipient Bearing Fault Extraction based on an Adaptive Multi-stage Noise Reduction Method
Authors: Tian Shaoning , Feng Guojin , Meng Zhaozong , Liu Xiaoang , Zhen Dong , Gu Fengshou
Published: June 2024

Considering the strong nonlinear and non-stationary characteristics of rolling bearing vibration signals, this paper proposes a multi-stage noise reduction method using adaptive variational mode decomposition and modulation signal bispectrum (AVMD-MSB) to extract the fault features of rolling bearings. Firstly, the AVMD is employed to adaptively select VMD parameters K and α and decompose the signal into a series of Intrinsic mode functions (IMFs), which allows an adaptive selection of the parameters of VMD. Then, all IMF components are reconstructed with weights according to the index of correlation kurtosis to avoid accidental omission of the IMFs containing important fault information. Finally, MSB is implemented to further suppress residual noises and interference components in the signal, precisely extract the bearing fault features. Numerical simulation and case study show that the AVMD-MSB is more advantageous in extracting fault characteristics from rolling bearing vibration signals compared with AVMD-Envelope and conventional VMD-MSB.
The influence of corrosion time on the observation of metallographic structure of 20CrMnMo
Authors: Liu Qing , Yang Suliang , Liu Huan , Chen Ke , He Xindang
Published: June 2024

20CrMnMo is one of the most widely used alloy steels, and its mechanical properties are closely related to the metallographic structure of the material. Clearly obtaining the distribution pattern of metallographic structure is of great significance for studying the mechanical properties of 20CrMnMo. In this paper, 20CrMnMo samples were subjected to corrosion treatment at different times, and the microstructure of the samples was observed by optical microscope (OM) and Scanning electron microscope (SEM). Through optical microscope observation, the metallographic structure images under different magnification and corrosion time were compared and analyzed, and the best corrosion time interval for metallographic structure observation was obtained; On this basis, by using Scanning electron microscope and EDS, the microscopic images at higher magnification were obtained, and the mechanism of corrosion time on the metallographic structure was further analyzed and explained.
Research on Thermocouple Integration Method of Hollow Thin-Walled Turbine Rotor Blade Surface
Authors: Fang Jianfeng
Published: June 2024

The hollow thin-walled structure is increasingly used in advanced aero-engine turbine rotor blades, and the traditional surface temperature measurement method based on groove buried couple is no longer applicable. In this paper, a new thermocouple integration method is proposed. The laser additive manufacturing process is used to generate thermocouple embedding channels on the surface of turbine blades. After the thermocouple is embedded, it is pre-fixed, and the thermocouple protection is realized by supersonic flame spraying technology. The strength of the thermocouple integrated structure of the turbine blade is verified by finite element analysis. Based on CFD analysis, the influence of thermocouple integration on the efficiency, pressure ratio and temperature distribution of the turbine blade is studied. The high-speed rotation test shows that the thermocouple integrated structure has high strength and reliability and meets the measurement requirements. This method can provide technical support for the surface temperature measurement of hollow thin-walled turbine rotor blades.
Modeling and Analysis of Inertial-Hydraulic Power take-off Device
Authors: Jia Han , Pei Zhongcai , Tang Zhiyong
Published: June 2024

This paper introduces a novel power output device that combines inertia and hydraulics, which captures vibrations caused by external forces acting on the carrier in space using the sensitive gyroscope of the inertia system. The captured random mechanical energy is then converted into hydraulic energy, rectified and regulated by the hydraulic system, and transformed into stable output energy. The influence of gyroscope angular momentum on the energy capturing capability is investigated through the development of a dynamic model. Additionally, a hydraulic power output system is designed, and the effect of hydraulic accumulator parameters on energy absorption fluctuations is analyzed. This research offers valuable insights for the design and optimization of the device.
Horizontal Tail Flight Load Prediction Method for Large UAVs based on Machine Learning
Authors: Hu Xiaomin , Pan Xiangyu , Wang Jiulong
Published: June 2024

In today’s rapidly developing large UAVs field, flight safety and reliability are essential considerations. Flight load is one of the important factors affecting the load capacity of large UAVs, so the research on load prediction technology can improve flight safety and the reliability of air transportation. This paper first introduces the collection and processing method of flight load data, then uses the machine learning method-BP neural network to predict flight load, establishes the BP neural network model to predict flight load with flight parameters, and optimizes the model according to error analysis. Finally, the accuracy and practicability of the model are verified by analysing the fitting of the training set and the test set, and the error distribution of the true value of shear, bending moment, torque and the absolute percentage of the predicted value, and the model is evaluated.
Study on the mechanical properties and optimization methods of high-strength high-modulus carbon fibre composite with the cap structure
Authors: Dong Zhicheng , Wang Jianing , Wan Xiaopeng
Published: June 2024

The application of high-strength, high-modulus carbon fiber with excellent properties such as high modulus, conductivity, and thermal conductivity has been increasingly widespread in aerospace flight, deep space exploration, and near-space vehicles. In recent years, with the continuous enhancement of functional requirements for products in these domains, there is a growing need to optimize the typical structure of such carbon fibers to enhance their load-bearing capacity. Therefore, in this study, we first conducted basic mechanical performance tests on specimens of T1100/5405 composite materials to obtain fundamental mechanical performance parameters of the material. Subsequently, compression and bending performance tests were performed on a typical hat-shaped structure to understand its actual load-bearing capacity and failure modes. The results indicate that the compressive failure load and bending failure load of the hat-shaped structure are 474.44 kN and 27.365 kN, respectively. Additionally, by combining the fundamental mechanical performance parameters of the composite material, the mechanical performance of the hat-shaped structure was simulated and verified using finite element analysis software, with the model validated using experimental data. Finally, layering parameters of the established finite element model were optimized, resulting in an increase of the structure’s load-bearing capacity under compression and bending loads to 662.629 kN and 31.9059 kN, respectively. In conclusion, the optimization approach presented in this paper for the T1100/5405 composite material’s hat-shaped structure is efficient. It yields noticeable improvements, significantly enhancing the load-bearing capacity of the typical structure in various application scenarios.
Study on Thermodynamic Coupling Performance of Multi-Level Lattice Structures
Authors: Yan Jiaqi , Han Tianyi , Huang Heyuan
Published: June 2024

With the development of hypersonic vehicle, the design of heat-resistant and load-bearing surface of hypersonic vehicle has gradually become a key technology affecting its combat effectiveness. As a new type of lightweight and high-strength structure, lattice structure has excellent mechanical properties such as ultra-light, high specific strength and high specific stiffness, and special properties such as vibration reduction, heat dissipation and sound absorption. Among them, the multi-level lattice structure can increase the bearing efficiency of the structure at low relative density, and increase the heat transfer area at the same time, so as to improve the heat protection and bearing capacity of the structure. This study includes three aspects of high temperature out-of-plane compression test, high temperature numerical simulation comparison, and structural optimization for the designed multi-level pyramid lattice, in order to obtain the bearing capacity of the multi-level pyramid lattice at 350°C, and further improve the bearing performance by optimizing the core structure. Through experiments and verification, the multi-level pyramid lattice designed and optimized in this study can further meet the requirements of thermal protection and load-bearing performance of aircraft compared with the single-level pyramid lattice, and can provide a reference for the study of high temperature mechanical properties of lattice structures, the design of new multi-level lattice structures and the engineering application of lattice structures.
The microstructures and mechanical properties of the TC4 titanium alloy fabricated by laser composite manufacturing technology
Authors: Kun He , Suming Chen , Yazhou Zhang
Published: June 2024

The effective combination of traditional forging and laser three-dimensional forming technology can play a crucial role in the preparation of large metal part with fine structures, thereby accelerating the manufacturing cycle of parts and reducing costs. This study used laser composite manufacturing technology to perform complete annealing heat treatment on TC4 titanium alloy structural part produced from traditional forgings. The analysis of microscopic structure, chemical composition, and mechanical properties has verified that the overall mechanical properties consistency of the composite manufacturing part has been effectively improved. The results indicate that laser composite manufacturing part have good metallurgical bonding, and there is no component segregation phenomenon in the composite manufacturing area. After complete annealing, the α lath in the composite manufacturing part is coarsened, the strength of the laser forming area is reduced, and the consistency of mechanical properties of the forging area and the laser forming area is enhanced. The consistency of strength of the two areas is increased from 78% before heat treatment to 84%.
Surface Defect Detection: A feature-based transfer learning approach
Authors: Abdul Majeed Anwar P.P. , Abdullah Muhammad Amirul , Ab. Nasir Ahmad Fakhri , Mohd Razman Mohd Azraai , Chen Wei , Yap Eng Hwa
Published: June 2024

Surface defect detection is critical for maintaining product quality in manufacturing. In this work, we apply a feature-based transfer learning approach for surface defect classification on the NEU surface defect database. The database contains defects across 6 categories captured under various conditions. We utilised two pretrained convolutional neural network (CNN) architectures - VGG16 and InceptionV3 - by removing the final classification layer and using the CNN as a fixed feature extractor. The output feature vectors were classified using a logistic regression (LR) model. The data was split into train, validation, and test sets with a 70:15:15 ratio. The VGG16-LR model achieved classification accuracy (CA) of 100%, 98%, and 99% for the train, validation, and test sets respectively. The InceptionV3-LR model attained CA of 100%, 91%, and 92% for train, validation, and test. The results demonstrate the effectiveness of transfer learning with CNN feature extraction for surface defect detection on challenging multi-category industrial datasets. Further work includes tuning hyperparameters and evaluating additional architectures.
Prediction of aircraft cabin noise by statistical energy analysis
Authors: Song Xiao , Xu Jiaxin , Lin Ziqi
Published: June 2024

The noise level in the aircraft cabin is an important indicator on market competitiveness, and it is a considerable challenge to reduce the noise in the cabin at a relatively small cost, so efficient and accurate forecasting tools are required. In the aviation industry, Statistical Energy Analysis (SEA) is widely used to predict mid- and high-frequency noise in aircraft cabins. It has the advantages of simple method and low requirement of structure details. This paper models the cabin of a certain type of aircraft, and uses statistical energy methods to predict the noise level in the cabin during ground and cruise conditions. Among them, the prediction result of the cabin noise on the ground is in good agreement with the test results above 250Hz, which verifies the correctness of the model. During cruise, the pressure fluctuation on the outer surface of the front fuselage is dominated by turbulent boundary layer noise. The analysis shows that the Robertson model can predict turbulent boundary layer noise well, and the difference between the predicted single-point spectrum and the experimental value is less than 1dB. The cabin noise predicted by only loading the turbulent boundary layer noise source is consistent with the experimental results, but the sound pressure level in some frequency bands is low.
Optimising liquid impingement jet arrays for concentrated heat sources
Authors: Elliott J W , Byrne G , Robinson A J
Published: June 2024

This work seeks to investigate jet array impingement liquid cooling of CPU processors that utilise Integrated Heat Spreaders. In this study, single and centralised heat sources of various sizes (10 mm to 20 mm) were investigated, and a series of single and multi-objective optimisation studies were carried out to determine the optimum arrangement of microjets for different heat source sizes based on variable geometric inputs of the jet orifice plate. The results indicated that the design of the optimum jet orifice strongly depends on the size of the heat source as well as whether the target optimisation strategy is to achieve minimum thermal resistance, or both minimum thermal resistance and minimum pumping power simultaneously. A clustering of quite different orifice designs in optimal zones is observed, where approximately the same hydraulic and/or thermal performance is observed.
Highly-turbulent packed bed heat exchange: modelling, experiment and validation
Authors: Simpson H , Lagarde J
Published: June 2024

SynchroStor Ltd. is developing a system for Pumped Thermal Energy Storage (PTES) based on the closed Brayton cycle principle. A numerical model of the gas-solid heat exchanger used by the cycle was developed in MATLAB to both evaluate the performance of the proposed arrangement and act as a design tool. A series of physical tests were run on a reduced-scale experimental test rig to assist with validation of the model. Thermal resistance due to radial conduction through the solid particles was found to be a critical feature of the model for SynchroStor’s design conditions; model outputs matched temperatures measured at each thermocouple station of the test rig with accuracies better than ±4.0%. The model was experimentally-validated for flows with superficial Reynolds numbers (Re) in the range 4,300 to 11,100.
Study of the thermal dynamic behavior of a rectangular enclosure with fins embedded in PCM
Authors: El Hanafi Abderrahmane , Blet Nicolas , Kheiri Abdelhamid , Remy Benjamin
Published: June 2024

This paper investigates the behavior of a Thermal Energy Storage (TES) system with Phase Change Material (PCM) embedded in fins. A commercial Computational Fluid Dynamics software is used to study the behavior of the system. A validation of the numerical model is done by comparing the numerical results with the measured melting fraction as function of time, determined from measurement of the temperature fields, for two lengths of fins. A dimensionless number is suggested to analyze the effect of the fins on the heat transfer in the medium. This study presents some results on the evolution of the liquid fraction and the Nusselt number. Results show that although the small conductivity of the PCM, the convection and conduction play a key role in heat transfer, their importance depends on the length of the fins. Furthermore, some feature of the behavior of the system without fins have been conserved by analyzing the Nusselt number.
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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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.
Thermodynamic effects in cavitating flow
Authors: Petkovšek Martin
Published: June 2024

Cavitation is a phenomenon characterized by vapor generation and condensation in liquid flows, at approximately constant temperature. Cavitation is usually triggered by a local pressure drop in the vicinity of a cavitation nucleus. As the bubble grows, latent heat is supplied from the surrounding liquid to the interface, creating a thermal boundary layer. This creates a thermal boundary layer. The result is a local drop in the liquid temperature, which leads to a drop in vapor pressure. This delays the further development of the bubble, as a greater pressure drop is required to maintain the process. This phenomenon is known as thermal delay or thermodynamic effect and plays a moderating role in the development of cavitation. Thermodynamic effects can usually be neglected for liquids whose critical temperature is much higher than the operating temperature. However, this is not the case for liquids whose operating temperature is close to the critical temperature, such as in cryogenics.

The understanding of the thermodynamic effects of cavitating flow is crucial for applications like turbopumps for liquid hydrogen LH2 and oxygen LOx in space launcher engines. Experimental studies of this phenomenon are rare as most of them were performed in the 1960s and 1970s. Due to the extreme difficulties of experimental investigation, predicting of thermodynamic effects in cavitation often bases on data in liquids other than cryogenics. Most often used surrogate liquids are hot water or certain refrigerants, which are selected by a single fluid property, most commonly by the thermodynamic parameter ∑.