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Comparison of Direct Pore-Scale and Volume-Averaging Methods for the Performance Evaluation of Porous Volumetric Solar Receiver

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Journal of Thermal science 2024年第5期33卷 1607-1617页

作者： DU Shen HE Yaling LI Dong LIU Zhanbin LI Mengjie National Innovation Platform(Center)for Industry-Education Integration of Energy Storage Technology Key Laboratory of Thermo-Fluid Science and Engineering of Ministry of EducationXi’an Jiaotong UniversityXi’an710049China

Direct pore-scale and volume-averaging numerical simulations are two methods for investigating the performance of porous volumetric solar *** clarify the difference in the prediction of heat transfer processes,a direct comparison between these two methods was conducted at both steady state and transient *** numerical models were established based on X-ray computed tomography scans and a local thermal non-equilibrium model,*** empirical parameters,which are indispensable to the volume-averaging simulation,were determined by Monte Carlo ray tracing and direct pore-scale numerical *** predicted outlet air temperature of the receiver by the volume-averaging simulation method corresponded satisfactorily to that in the direct pore-scale *** largest discrepancies were observed when the receiver's working temperature was elevated,with differences of 5.5%and 3.68%for the steady state and transient state simulations,***,the volume-averaging method is incapable of capturing the local temperature information of the air and porous *** underestimates the inlet temperature of the receiver,leading to an overestimation of the receiver's thermal efficiency,with the largest difference being 6.51%.The comparison results show that the volume-averaging model is a good approximation to the pore-scale model when the empirical parameters are carefully selected.

关键词： porous media volumetric solar receiver pore-scale method volume-averaging method thermal performance

Mechanism of capture section affecting an intake for atmosphere-breathing electric propulsion

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Chinese Journal of Aeronautics 2024年第1期37卷 51-63页

作者： Siyuan ZHANG Jinyuan YANG Cheng LI Haolin LI Liwei ZHANG Liang DING Anbang SUN State Key Laboratory of Electrical Insulation and Power Equipment School of Electrical EngineeringXi’an Jiaotong UniversityXi’an 710049China China Academy of Aerospace science and Innovation Beijing 100049China

Atmosphere-Breathing Electric Propulsion(ABEP)can compensate for lost momentum of spacecraft operating in Very Low Earth Orbit(VLEO)which has been widely concerned due to its excellent commercial *** is a key technology to improve the capture efficiency of intakes,which collect and compress the atmosphere for *** this paper,the mechanism of the capture section affecting capture efficiency is investigated by Test Particle Monte Carlo(TPMC)simulations with 3D intake *** inner surface smoothness and average collision number are determined to be key factors affecting capture efficiency,and a negative effect growth model is accordingly *** the inner surface smoothness is less than 0.2,the highest capture efficiency and its corresponding average collision number interval are independent of the capture section’s geometry and its mesh *** the inner surface smoothness is higher than 0.2,the capture efficiency will decrease by installing any capture *** on the present results,the manufacturing process and material selection are suggested to be prioritized during the intake geometry design in engineering ***,the highest capture efficiency can be achieved by adjusting the length and mesh size of the capture section.

关键词： Atmosphere-breathing electric propulsion Capture efficiency Capture section Intake Test particle Monte Carlo Very low earth orbit

Measurement,Modelling and Analysis of Residence Time Distribution Characteristics in a Continuous Hydrothermal Reactor

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Journal of Thermal science 2024年第4期33卷 1301-1311页

作者： LI Yi ZHAI Binjiang WANG Junying WANG Weizuo JIN Hui State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong UniversityXi’an710049China

Understanding the residence time distribution(RTD)of a continuous hydrothermal reactor is of great significance to improve product quality and reaction *** this work,an on-line measurement system is attached to a continuous reactor to investigate the characteristics of *** approach that can accurately fit and describe the experimental measured RTD curve by finding characteristic values is proposed for analysis and *** RTD curves of three experiment groups are measured and the characteristic values are *** show that increasing total flow rate and extending effective reactor length have inverse effect on average residence time,but they both cause the reactor to approach a plug flow reactor and improve the materials *** branch flow rate fraction has no significant effect on RTD characteristics in the scope of the present work except the weak negative correlation with the average residence ***,the natural convection stirring effect can also increase the average residence time,especially when the forced flow is *** analysis reveals that it is necessary to consider the matching of natural convection,forced flow and reactor size to control RTD when designing the hydrothermal reactor and working conditions.

关键词： continuous reactor residence time distribution modelling

Laminar Flame Structure-Dependent Exergy Destruction Behavior at Auto-Ignition Time Scale:A Case Study of Dimethyl Ether(DME)

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Journal of Thermal science 2024年第4期33卷 1257-1271页

作者： WU Honghuan HUANG Wenlin ZHAO Hao SUN Wuchuan HUANG Zuohua ZHANG Yingjia State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong UniversityXi’an710049China

Hybrid deflagration/auto-ignition flame structures coexist in the combustion of advanced *** exergy destruction caused by different irreversible processes under varied flame regimes is thus important for understanding engine *** this study,the flame propagation modes for the premixed DME/air mixtures are numerically investigated under engine-relevant *** entropy generation and exergy destruction characteristics are compared under different flame *** reveal that as the typical premixed flame transition towards auto-ignition front,the exergy destruction from heat conduction and species mass diffusion gradually vanish and are dominated by chemical *** distributions of temperature and species mole fraction in the flame domain are analyzed to clarify the exergy destruction behaviors caused by heat conduction and mass ***,by dividing the DME oxidation process into four stages,the main reaction channels that contribute to the increase in exergy destruction from chemical reaction have been *** is found that the production and consumption of CH_(2)O and HO_(2) radical dominate the exergy destruction behavior during DME *** this basis,the kinetic mechanism of low-temperature chemistry causing greater exergy destruction is ***,low-temperature chemistry leads to significant exergy destruction due to(a)the large irreversibility of itself and(b)(mainly)the enhancement of H_(2)O_(2)loop reactions by low-temperature reaction *** the reduction of combustion irreversibility is promising to be achieved by reasonably regulating the fuel oxidation path.

关键词： exergy destruction flame structures entropy generation low-temperature chemistry DME

A novel efficient energy absorber with free inversion of a metal foam-filled circular tube

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Applied Mathematics and Mechanics(English Edition) 2024年第1期45卷 1-14页

作者： Jianxun ZHANG Jinwen BAI State Key Laboratory for Strength and Vibration of Mechanical Structures School of Aerospace EngineeringXi'an Jiaotong UniversityXi'an 710049China

In this paper, a novel efficient energy absorber with free inversion of a metal foam-filled circular tube(MFFCT) is designed, and the axial compressive behavior of the MFFCT under free inversion is studied analytically and numerically. The theoretical analysis reveals that the energy is mainly dissipated through the radial bending of the metal circular tube, the circumferential expansion of the metal circular tube, and the metal filled-foam compression. The principle of energy conservation is used to derive the theoretical formula for the minimum compressive force of the MFFCT over free inversion under axial loading. Furthermore, the free inversion deformation characteristics of the MFFCT are analyzed numerically. The theoretical steady values are found to be in good agreement with the results of the finite element(FE) analysis. The effects of the average diameter of the metal tube, the wall thickness of the metal tube, and the filled-foam strength on the free inversion deformation of the MFFCT are considered. It is observed that in the steady deformation stage, the load-carrying and energy-absorbing capacities of the MFFCT increase with the increase in the average diameter of the metal tube, the wall thickness of the metal tube, or the filled-foam strength. The specific energy absorption(SEA) of free inversion of the MFFCT is significantly higher than that of the metal tube alone.

关键词： metal foam-filled circular tube(MFFCT) free inversion load-carrying capacity energy absorption

Design strategies of high-performance lead-free electroceramics for energy storage applications

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Rare Metals 2024年第3期43卷 853-878页

作者： Biao Guo Fei Jin Li Li Zi-Zhao Pan xin-Wei Xu Hong Wang Department of Materials science and Engineering College of EngineeringSouthern University of Science and TechnologyShenzhen518055China School of Microelectronics and State Key Laboratory for Mechanical Behavior of Materials Xi’an Jiaotong UniversityXi’an710049China

A greater number of compact and reliable electrostatic capacitors are in demand due to the Internet of Things boom and rapidly growing complex and integrated electronic systems,continuously promoting the development of high-energy-density ceramic-based *** significant successes have been achieved in obtaining high energy densities in lead-based ferroelectric ceramics,the utilization of lead-containing ceramies has been restricted due to environmental and health hazards of ***-free ferroelectric ceramics have garnered tremendous attention and are expected to replace lead-based ceramics in the near ***,the energy density of lead-free ceramics is still lagging behind that of lead-containing ***,severely limiting their *** efforts have been made to enhance the energy storage performance of lead-free ceramics using multi-scale design strategies,and exciting progress has been achieved in the past *** review briefly discusses the energy storage mechanism and fundamental characteristics of a dielectric capacitor,summarizes and compares the state-of-the-art design strategies for high-energy-density lead-free ceramics,and highlights several critical issues and requirements for industrial *** prospects and challenges of lead-free ceramics for energy storage applications are also discussed.

关键词： Dielectric materials Lead-free ceramic Environment friendly Energy storage Design strategy

Transfer learning and neural networks in predicting quadrupole deformation

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Chinese Physics C 2024年第6期48卷 162-168页

作者：原林李佳星张鸿飞 School of science Xi'an Polytechnic UniversityXi'an 710048China Engineering Research Center of Flexible Radiation Protection Technology Universities of Shaanxi ProvinceXi'an 710048China xi'an Key Laboratory of Nuclear Protection Textile Equipment Technology Xi'an 710048China School of Physics Xi'an Jiaotong UniversityXi'an 710049China School of Nuclear science and Technology Lanzhou UniversityLanzhou 730000China

Accurately determining the quadrupole deformation parameters of atomic nuclei is crucial for understanding their structural and dynamic *** study introduces an innovative approach that combines transfer learning techniques with neural networks to predict the quadrupole deformation parameters of even-even *** the application of this innovative technique,the quadrupole deformation parameters of 2331 even-even nuclei are successfully predicted within the nuclear region defined by proton numbers 8≤Z≤134 and neutron numbers N≥***,we discuss the impact of nuclear quadrupole deformation parameters on the capture cross-sections in heavy-ion fusion reactions,reconstructing the capture cross-sections for the reactions ^(48)Ca+^(244)Pu and ^(48)Ca+^(248)*** research offers new insights into the application of neural networks in nuclear physics and highlights the potential of merging advanced machine learning techniques with both theoretical and experimental data,particularly in fields where experimental data are limited.

关键词： nuclear deformation neural networks transfer learning heavy-ion fusion reactions

Mechanical Janus lattice with plug-switch orientation

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Theoretical & Applied Mechanics Letters 2024年第1期14卷 23-26页

作者： Yupei Zhang Jiawei Zhong Zhengcai Zhao Ruiyu Bai Yanqi Yin Yang Yu Bo Li State Key Laboratory for Manufacturing System EngineeringShaanxi Key Laboratory of Intelligent Robots School of Mechanical Engineering Xi’an Jiaotong UniversityXi’an 710049China Qian Xuesen Honors College Xi’an Jiaotong UniversityXi’an 710049China

In recent years,materials with asymmetric mechanical response properties(mechanical Janus materials)have been found possess numerous potential applications,*** absorption and vibration *** this study,we propose a novel mechanical Janus lattice whose asymmetric mechanical response can be switched in orientation by a *** finite element analysis and experimental verification,this lattice exhibits asymmetric displacement responses to symmetric ***,with such a plug structure inside,individual lattices can switch the orientation of asymmetry and thus achieve reprogrammable design of a mechanical structure with chained *** reprogrammable asymmetry of this material will offer multiple functions in design of mechanical metamaterials.

关键词： Janus Non-reciprocity Programmability Mechanical metamaterial

QAAS:quick accurate auto-scaling for streaming processing

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Frontiers of Computer science 2024年第1期18卷 5-15页

作者： Shiyuan LIU Yunchun LI Hailong YANG Ming DUN Chen CHEN Huaitao ZHANG Wei LI State Key Laboratory of Software Development Environment Beijing 100191China School of Computer science and Engineering Beihang UniversityBeijing 100191China School of Cyber science and Technology Beihang UniversityBeijing 100191China School of Computer science and Technology Xi’an Jiaotong UniversityXi’an 710049China

In recent years,the demand for real-time data processing has been increasing,and various stream processing systems have *** the amount of data input to the stream processing system fluctuates,the computing resources required by the stream processing job will also *** resources used by stream processing jobs need to be adjusted according to load changes,avoiding the waste of computing *** present,existing works adjust stream processing jobs based on the assumption that there is a linear relationship between the operator parallelism and operator resource consumption(e.g.,throughput),which makes a significant deviation when the operator parallelism *** paper proposes a nonlinear model to represent operator *** divide the operator performance into three stages,the Non-competition stage,the Non-full competition stage,and the Full competition *** our proposed performance model,given the parallelism of the operator,we can accurately predict the CPU utilization and operator *** with actual experiments,the prediction error of our model is below 5%.We also propose a quick accurate auto-scaling(QAAS)method that uses the operator performance model to implement the auto-scaling of the operator parallelism of the Flink *** to previous work,QAAS is able to maintain stable job performance under load changes,minimizing the number of job adjustments and reducing data backlogs by 50%.

关键词： stream processing performance model auto-scaling