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Design Optimization and Operating Performance of S-CO_(2) Brayton Cycle under Fluctuating Ambient Temperature and Diverse power Demand Scenarios

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Journal of thermal science 2024年第1期33卷 190-206页

作者： YANG Jingze YANG Zhen DUAN Yuanyuan Key Laboratory for Thermal Science and Power Engineering of MOE Beijing Key Laboratory for CO_(2) Utilization and Reduction TechnologyTsinghua UniversityBeijing 100084China

The supercritical CO_(2)(S-CO_(2)) Brayton cycle is expected to replace steam cycle in the application of solar power tower system due to the attractive potential to improve efficiency and reduce *** the concentrated solar power plant with thermal energy storage is usually located in drought area and used to provide a dispatchable power output,the S-CO_(2) Brayton cycle has to operate under fluctuating ambient temperature and diverse power demand *** addition,the cycle design condition will directly affect the off-design *** this work,the combined effects of design condition,and distributions of ambient temperature and power demand on the cycle operating performance are analyzed,and the off-design performance maps are proposed for the first time.A cycle design method with feedback mechanism of operating performance under varied ambient temperature and power demand is introduced *** show that the low design value of compressor inlet temperature is not conductive to efficient operation under low loads and sufficient output under high ambient *** average yearly efficiency is most affected by the average power demand,while the load cover factor is significantly influenced by the average ambient *** multi-objective optimization,the optimal solution of designed compressor inlet temperature is close to the minimum value of35℃ in Delingha with low ambient temperature,while reaches 44.15℃ in Daggett under the scenario of high ambient temperature,low average power demand,long duration and large value of peak load during the peak temperature *** the cycle designed with compressor inlet temperature of 35℃ instead of 44.15℃ in Daggett under light industry power demand,the reduction of load cover factor will reach 0.027,but the average yearly efficiency can barely be improved.

关键词： supercritical CO_(2)Brayton cycle ambient temperature fluctuating power demand scenarios design optimization off-design performance

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thermal Decomposition and Oxidative Decomposition Mechanism of HFC-134a by Experimental and DFT Method

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Journal of thermal science 2024年第5期33卷 1990-2003页

作者： XU Yunting ZHANG Kai DAI Xiaoye SHI Lin Key Laboratory for Thermal Science and Power Engineering of Ministry of Education Department of Energy and Power EngineeringTsinghua UniversityBeijing 100084China

In response to the Kigali Amendment to the Montreal Protocol and global low-carbon emission environmental requirements,the phase-out and decomposition of numerous HFC refrigerants have become urgent,necessitating efficient and mild decomposition *** study investigates the thermal decomposition and oxidative thermal decomposition pathways of the typical hydrofluorocarbon refrigerant HFC-134a,employing a combination of experimental and quantum chemical DFT simulation *** chemical simulations reveal that the initial reaction bond cleavage serves as the rate-determining step during the thermal decomposition process,with the most easily detectable closed-shell products including CF_(2)=CHF,HF,CH_(3)F,CHF_(3),CH_(2)F_(2),and CF_(4).Reactive oxygen species can significantly reduce the Gibbs free energy barrier for HFC-134a *** achieve efficient degradation of HFC-134a,appropriate catalysts should be developed and selected to increase the level of reactive oxygen species in the reaction *** studies further corroborate that HFC-134a may undergo degradation through distinct reaction pathways under varying temperature(240℃to360℃)and pressure(0.1 MPa to 4.5 MPa)conditions,in agreement with simulation predictions.

关键词： HFC-134a pyrolysis oxidative thermal decomposition DFT refrigerant

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Effects of the inlet particle spatial distribution on the performance of a gas-solid cyclone separator

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Particuology 2024年第2期85卷 133-145页

作者： Yuge Yao Manxia Shang Xiwei Ke Zhong Huang Tuo Zhou Junfu Lyu Key Laboratory for Thermal Science and Power Engineering of Ministry of Education Department of Energy and Power EngineeringTsinghua UniversityBeijing100084China

The present study was aimed at the inlet particle spatial distribution of a gas-solid separator with high solid loading and investigated its effects on cyclone performance and the inner flow *** flow fields of a cyclone with different rectangular particle flow areas on the inlet surface were numerically simulated using a four-way coupling *** simulated results indicate that reducing the inlet particle flow area and lowing the inlet particle position can effectively reduce the scattered particles inside the cyclone separator and enhance the separation *** gathering the particles to the centerline can also weaken the particle *** particles near the roof account for the swirling particle ceiling *** inlet particle spatial distribution affects the pressure drop mainly by affecting the gas tangential velocity in the cylinder ***,compared to the hori-zontal particle distribution on the inlet surface,the vertical particle distribution has greater effects on cyclone performance.

关键词： Gas-solid cyclone Inlet particle spatial distribution Four-way coupling Separation efficiency Scattered particle

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Energy Conversion and Transmission of Electric power Generation through Water Evaporation

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Journal of thermal science 2025年第2期34卷 413-428页

作者： CHEN Liang WANG Lu WANG Xinyi ZHANG Bo LI Zhen Key Laboratory for Thermal Science and Power Engineering of Ministry of Education Department of Engineering MechanicsTsinghua UniversityBeijing100084China

Water is a recyclable resource and the largest energy carrier on *** hydropower generation technologies hold great promise for the ***,there is a lack of evaluation standards for power generation ***,the mechanism of hydrovoltaic power generation lacks systematic *** this study,a thermodynamic analysis method about hot and humid air energy conversion based on the principle of hydropower generation is *** author's knowledge,it is the first time that the maximum available energy of hydropower generation is analyzed by exergy and parametric *** greater the difference,the higher the available ***,a series of experiments were conducted to explore the power generation device materials,structural composition,and structural parameters,further clarifying the principle of electricity ***,the influence of temperature and relative humidity on the power generation performance was also *** increase in temperature can effectively increase the output electrical performance of the power *** open-circuit voltage and short-circuit current of water evaporation power generation with Al_(2)O_(3)nanoparticles are higher than 2.5 V and 150 nA *** analysis,we propose relevant application strategies to provide theoretical and practical support for the development of green energy.

关键词： exergy analysis green energy new hydropower generation flexible power generation devices

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Constraint-incorporated deep learning model for predicting heat transfer in porous media under diverse external heat fluxes

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Energy and AI 2024年第4期18卷 136-150页

作者： Ziling Guo Hui Wang Huangyi Zhu Zhiguo Qu MOE Key Laboratory of Thermal-Fluid Science and Engineering School of Energy and Power EngineeringXi’an Jiaotong UniversityXi’anShaanxi 710049China

The temperature field within porous media is considerably affected by different boundary conditions,and effective thermal conductivity varies with spatial structure *** present,traditional prediction methods for the temperature field are expensive and time consuming,particularly for large structures and di-mensions,whereas deep learning surrogate models have limitations related to constant boundary conditions and two-dimensional input slices,lacking the three-dimensional topology and spatial ***,a constraint-incorporated model using U-Net architecture as the backbone is proposed to predict the temperature field and effective thermal conductivity of sphere-packed porous media,considering diverse external heat fluxes.A total of 510 original samples of temperature fields are generated through lattice Boltzmann method(LBM)simulations,which are further augmented to 33,150 samples using the self-amplification method for the *** prior knowledge is incorporated into the model to constrain the training direction by adding physical constraint terms as well as adaptive weights to the loss *** vectors with different heat fluxes and porosities are embedded into latent features for predicting different boundary *** indicate that the constraint-incorporated model has a mean relative error ranging between 1.1%and 5.7%compared with the LBM results in the testing *** exhibits weak dependence on the database size and substantially reduces computational time,with a maximum speedup ratio of 7.14×10^(6).This study presents a deep learning model with physical constraints for predicting heat conduction in porous media,alleviating the burden of extensive experiments and simulations.

关键词： Porous media Lattice Boltzmann method Temperature field Deep learning Constraint-incorporated model

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Multi-objective optimization of laser perforated fuel filter parameters based on artificial neural network and genetic algorithm

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Particuology 2025年第1期96卷 57-70页

作者： Yifan Wang Tianyi Zhang Lei Chen Wenquan Tao Key Laboratory of Thermo-Fluid Science and Engineering MOESchool of Energy and Power EngineeringXi'an Jiaotong UniversityXi'an710049China

In precise fuel circuit systems, the filtration of particulate impurities seriously affects the efficiency and service life of various components. For filtration process intensification of high-pressure fuel laser perforated filters, the two-phase flow characteristics in filters is studied. The size, position and number of filtration holes are taken as optimization variables, and take the filtration efficiency and flow pressure drop as optimization objectives. Computational fluid dynamics (CFD) is used to simulate the two-phase motion of continuous phase and discrete particles in a periodic unit. Artificial neural networks (ANN) are utilized for objectives prediction, and the NSGA-II genetic algorithm is employed for multi-objective optimization, resulting in the Pareto front solution set. Furtherly, the reasonable solution is selected by introducing TOPSIS to ensure that two optimization indexes are relatively smaller and balanced. The optimized filter element scheme allows the filter to have a pressure drop of less than 3.2 MPa under high pressure and a filtration efficiency of over 80% for spherical particle impurities with a diameter of 5 μm or more.

关键词： Fuel filter Multiphase flow Neural network Genetic algorithm Multi-objective optimization Particle

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Efficient and highly selective photocatalytic reduction of Cr(Ⅵ) by an active two-dimensional covalent organic framework

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Progress in Natural science:Materials International 2024年第5期34卷 933-941页

作者： Yuxuan Bai Yunzi Wang Junyu Chen Keda Zhu Jianjun Wang MOE Key Laboratory of Resources and Environmental Systems Optimization College of Environmental Science and Engineering North China Electric Power University

In this paper, a two-dimensional covalent organic framework material（named HDU-27） with thiazole structure and π-π conjugation has been successfully synthesized using the ligands tri acetaldehyde-based methoxyphenyl and benzo [1,2-d:4,5-d]thiazole-2,6-diamine in an ammonia-formaldehyde condensation reaction and applied to the photocatalytic reduction study of chromium（Cr）. The photocatalytic experiments showed that HDU-27 had an excellent photocatalytic reduction of Cr（VI） with a high Cr（VI） reduction efficiency of 99.5 % at pH = 2 for 60min. In the presence of interfering ions, HDU-27 exhibited excellent selectivity for Cr（VI）. Mechanistic experiments and electron spin resonance characterization identified e-and ·O-2radicals as the main active species in Cr（VI） photocatalytic reduction. In addition, the photocatalytic rate of HDU-27 was significantly accelerated in the Cr（VI）/organic pollutant（RhB, MB, MO） mixed system due to the oxidation of the organic matter and the increase in the separation of photogenerated e--h+. The cycling experiments demonstrated the excellent reduction stability and recyclability of HDU-27 in the photocatalytic reduction of Cr（VI）. HDU-27 is an excellent photocatalyst with potential application for removing organic pollutants and heavy metal ions from contaminated wastewater.

关键词： Covalent organic framework HDU-27 Photocatalysis Chromium reduction

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Modeling of Packed Bed Methanol Steam Reformer Integrated with Tubular High Temperature Proton Exchange Membrane Fuel Cell

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Journal of thermal science 2023年第1期32卷 81-92页

作者： LIU Menghua SHI Yixiang CAI Ningsheng Key Laboratory for Thermal Science and Power Engineering of Ministry of Education Department of Energy and Power EngineeringTsinghua UniversityBeijing 100084China

This work proposes a novel tubular structure of high-temperature proton exchange membrane fuel cell(PEMFC)integrated with a built-in packed-bed methanol steam reformer to provide hydrogen for power output.A two-dimensional axisymmetric non-isothermal model was developed in COMSOL Multiphysics 5.4 to simulate the performance of a tubular high temperature proton membrane fuel cell and a packed bed methanol *** model considers the coupling multi-physical processes,including methanol reforming reaction,water gas shift reaction,methanol cracking reaction as well as the heat,mass and momentum transport *** sub-model of the tubular packed-bed methanol reformer is validated between 433 K and 493 K with the experimental data reported in the *** sub-model of the high temperature proton exchange fuel cell is validated between 393 K and 433 K with the published *** results show that power output and temperature distribution of the integrated unit depend on methanol flow rates and working *** was suggested that stable power generation performance of 0.14 W/cm_(2)and temperature drop in methanol steam reformer of≤10 K could be achieved by controlling the methanol space-time ratio of≥250 kg·s/mol with working voltage at 0.6 V,even in the absence of an external heat source.

关键词： high temperature proton exchange membrane fuel cell methanol steam reformer tubular PEMFC hydrogen production Multiphysics modeling

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Observation of ballistic-diffusive thermal transport in GaN transistors using thermoreflectance thermal imaging

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Rare Metals 2024年第1期43卷 389-394页

作者： Zhi-Ke Liu Yang Shen Han-Ling Li Bing-Yang Cao Key Laboratory for Thermal Science and Power Engineering of Ministry of Education Department of Engineering MechanicsTsinghua UniversityBeijing 100084China

To develop effective thermal management strategies for gallium-nitride (GaN) transistors, it is essential to accurately predict the device junction temperature. Since the width of the heat generation in the devices is comparable to phonon mean free paths (MFPs) of GaN, phonon ballistic transport exists and can significantly affect the heat transport process.

关键词： temperature. transistors GaN

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A comprehensive review on microchannel heat sinks for electronics cooling

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International Journal of Extreme Manufacturing 2024年第2期6卷 133-162页

作者： Zhi-Qiang Yu Mo-Tong Li Bing-Yang Cao Key Laboratory for Thermal Science and Power Engineering of Ministry of Education Department of Engineering MechanicsTsinghua UniversityBeijing 100084People’s Republic of China

The heat generation of electronic devices is increasing dramatically,which causes a serious bottleneck in the thermal management of electronics,and overheating will result in performance deterioration and even device *** the development of micro-machining technologies,the microchannel heat sink(MCHS)has become one of the best ways to remove the considerable amount of heat generated by high-power *** has the advantages of large specific surface area,small size,coolant saving and high heat transfer *** paper comprehensively takes an overview of the research progress in MCHSs and generalizes the hotspots and bottlenecks of this *** heat transfer mechanisms and performances of different channel structures,coolants,channel materials and some other influencing factors are ***,this paper classifies the heat transfer enhancement technology and reviews the related studies on both the single-phase and phase-change flow and heat *** comprehensive review is expected to provide a theoretical reference and technical guidance for further research and application of MCHSs in the future.

关键词： microchannel heat sink thermal management of electronics microscale heat transfer heat transfer enhancement

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