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Performance analysis and optimization of a combined cooling and power system using low boiling point working fluid driven by engine waste heat

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ENERGY CONVERSION AND MANAGEMENT 2019年 180卷 962-976页

作者： Huang, Wenge Wang, Jiangfeng Xia, Jiaxi Zhao, Pan Dai, Yiping Xi An Jiao Tong Univ Sch Energy & Power Engn Inst TurbomachineryState Key Lab Multiphase Flow Shaanxi Engn Lab Turbomachinery & Power Equipment Xian 710049 Shaanxi Peoples R China

This paper develops a combined cooling and power system, which consists of a carbon dioxide Brayton cycle, a dual-pressure organic Rankine cycle and an ejector refrigeration cycle, to recover waste heat from exhaust gas and jacket water in internal combustion engines. Thermodynamic models of the system are performed and exergoeconomic methods are used to calculate the levelized exergy cost of the component products. Effects of seven parameters, including Brayton cycle turbine inlet temperature and inlet pressure, organic Rankine cycle turbine high-pressure side and low-pressure side inlet temperature and ejector primary inlet pressure, are evaluated. Single-objective optimization is carried out by means of genetic algorithm to obtain the minimum levelized exergy cost of system product. Results show that the increase of pressure at Brayton cycle turbine inlet and high-pressure and low-pressure side of the organic Rankine cycle turbine inlet contributes to the decrease of levelized exergy cost of the system product. Optimization results show that minimum levelized exergy cost for system product is 53.25 $ (MWh)(-1). When system product levelized exergy cost is minimum, system net power output, cooling capacity and exergy efficiency are 374.37 kW, 188.63 kW and 37.31%, respectively.

关键词： Internal combustion engine Brayton cycle Waste heat recovery Dual-pressure organic Rankine cycle Ejector refrigeration cycle Optimization

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Attenuated Periodical Oscillation Characteristics in a Nanoscale Particle-Laden Laminar flow

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INDUSTRIAL & engineering CHEMISTRY RESEARCH 2020年第16期59卷 8018-8027页

作者： Geng, Jiafeng Tang, Junwang Wang, Yechun Huang, Zhenxiong Jing, Dengwei Guo, Liejin Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Peoples R China Xi An Jiao Tong Univ Int Res Ctr Renewable Energy Xian 710049 Peoples R China UCL Dept Chem Engn London WC1E 7JE England

Transport properties in a nanoparticle-laden flow are of great importance for their practical use, such as in tubular reactor-based photocatalytic technologies. In our study, an experimental setup based on photocatalytic application was employed to investigate the nanoparticle transport characteristics in a flow reactor. An interesting periodical attenuated oscillation of the particle volume fraction and mean particle size with time was found in the nanoparticle-laden flow. We further analyzed the period of the attenuated oscillation curve by conducting a linear fitting, which shows that the period can be expressed as T = f(Q,L) in which the period is proportional to the length of the test section and inversely proportional to the flow rate. We found that the time 5T is a very important criterion for determining whether the particle suspension has reached the quasi-steady state and whether the nanoparticle has been well suspended. Our work is believed to be valuable, efficient, and effective in the study of transportation of nanoparticles in laminar flow with low energy consumption.

关键词： Particles Nanoparticles Oscillation Particle size Suspensions

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Novel rotary regenerative heat exchanger using cascaded phase change material capsules

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APPLIED THERMAL engineering 2021年 188卷

作者： Wang, Limin Wang, Chao Guo, Yalong Wu, Ying Bai, Wengang Che, Defu Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Peoples R China Inner Mongolia Power Res Inst Co Ltd Hohhot 010000 Peoples R China Xian Thermal Power Res Inst Co Ltd Xian 710054 Peoples R China

A novel rotary regenerative heat exchanger with cascaded phase change material (PCM) capsules was proposed and proved to be a better alternative to the traditional one. The rotary regenerative air preheater used in coal-fired power plant was taken as an example to comparatively analyze the performance characteristics of the rotary regenerative heat exchanger with latent heat storage material and the one with sensible heat storage material. The latent rotary regenerative air preheater (LRAPH) can achieve more uniform outlet temperature of air at low rotating speed than the sensible one (SRAPH), which is conductive to the measurement and process control in application. PCM capsule functions as both a latent heat storage material at its phase change temperature and as a sensible heat storage material at other temperature values. At lower rotating speed, more PCM capsules in LRAPH will work at the phase change temperature resulting in small temperature swings of fluid and matrix. The heat exchanger effectiveness is comparatively analyzed for SRAPH and LRAPH with different matrix parameters. The replacement of sensible heat storage materials by the latent ones would lead to an efficiency improvement of RAPH as large as 11% especially at lower rotating speed. The LRAPH is more capable to counter the entrainment leakage and the problems induced by temperature swings than traditional SRAPH. The cascaded distribution of PCM capsules with different phase change temperatures should be reasonably set according to the specific characteristics of temperature distribution in application to make full use of advantages of cascaded PCMs.

关键词： Cascaded phase change materials Packed bed Rotary regenerative heat exchanger Local thermal non-equilibrium model Thermal performance

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Comparison of Chemical Composition and Acidity of Size-Resolved Inorganic Aerosols at the Top and Foot of Mt. Hua, Northwest China: The Role of the Gas-Particle Distribution of Ammonia

SSRN

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SSRN 2023年

作者： Li, Jianjun Feng, Qiao Liu, Haijiao Dai, Wenting Cao, Yue Shen, Minxia Liu, Yali Qi, Weining Chen, Yukun Guo, Xiao Zhang, Yifan Li, Lu Zhou, Bianhong State Key Laboratory of Loess and Quaternary Geology Key Lab of Aerosol Chemistry and Physics Institute of Earth Environment Chinese Academy of Sciences Xi’an710061 China College of Geography and Environment Baoji University of Arts and Sciences Shaanxi Key Laboratory of Disaster Monitoring and Mechanism Simulation Baoji721013 China Xi’an Institute for Innovative Earth Environment Research Xi’an710061 China National Observation and Research Station of Regional Ecological Environment Change and Comprehensive Management in the Guanzhong Plain Shaanxi China State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an710049 China

Aerosol pH is not only a diagnostic indicator of secondary aerosol formation, but also a key factor in the specific chemical reaction routes that produce sulfates and nitrates. To understand the characteristics of aerosol acidity in the Mt. Hua, the chemical fractions of water-soluble inorganic ions in the atmospheric PM2.5 and size-resolved particle at the top and foot of Mt. Hua in summer 2020 were studied. The results showed the mass concentrations of PM2.5 and water-soluble ions at the foot were 2.0-2.6 times higher than those at the top. The secondary inorganic ions, i.e. SO42-, NO3-, and NH4+ (SNA) were 56%-61% higher by day than by night. SO42- was mainly distributed in the fine particles (Dp 2.1 µm) was mainly attributed to the gaseous HNO3 volatilized from fine particles reacting with cations in coarse particles to form non-volatile salts (such as Ca(NO3)2). The pH values of PM2.5 were 2.7 ± 1.3 and 3.3 ± 0.42 at the top and foot, respectively. NH4+/NH3(g) plays a decisive role in stabilising aerosol acidity. In addition, the increase of the liquid water content (LWC) at the foot facilitates the gas-particle conversion of NH3, while the H+ concentration was diluted, resulting in a decrease in acidity at the foot. NH4+/NH3 had good linear correlations with SO42−, NO3－, and LWC during the daytime at both sites, indicating that SO42−, NO3－, and LWC together affect the gas-particle distribution of ammonia by day: however, the effect of LWC at night was not evident. © 2023, The Authors. All rights reserved.

关键词： Ammonia

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Regeneration of iron fuel in fluidized beds Part II: Reduction experiments

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POWDER TECHNOLOGY 2023年 420卷

作者： Liu, X. Zhang, X. Li, J. Zhu, Q. Deen, N. G. Tang, Y. Eindhoven Univ Technol Dept Mech Engn Power & Flow Grp POB 513 NL-5600 MB Eindhoven Netherlands Chinese Acad Sci Inst Proc Engn State Key Lab Multiphase Complex Syst Beijing 100190 Peoples R China Univ Chinese Acad Sci Sch Chem Engn Beijing 100049 Peoples R China Eindhoven Univ Technol Eindhoven Inst Renewable Energy Syst EIRES POB 513 NL-5600 MB Eindhoven Netherlands

Direct reduction of combusted iron powders using renewable energy is one of the keys to ensure a carbon -neutral iron fuel cycle. Based on (de-)fluidization experimental study in Part I, reduction experiments of micron-sized combusted iron powders using hydrogen in a lab-scale gas-fluidized bed are conducted at temperatures ranging from 500 degrees C to 650 degrees C. The effects of temperature, hydrogen velocity and concentration on the reduction performance (including reduction degree, particle morphology and size change) and sintering/defluidization behavior are investigated. Overall, a reduction degree higher than 90% is reached at a lower temperature of 500 degrees C, whereas at higher temperatures the serious problem of particle sintering is encountered, which leads to quick defluidization and thus a relatively low reduction degree. Temperature has been found to have a pronounced effect on the sintering and reduction behavior, while the effect of gas velocity on the reduction process is negligible. SEM images show that the reduced powders are porous with the pore size increasing with temperature. These experimental findings provide insights for the design of industrial process of hydrogen-based regeneration of iron fuels.

关键词： Iron fuel Gas-fluidized bed Reduction performance Sintering Iron regeneration

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Study of an autothermal-equilibrium metal hydride reactor by reaction heat recovery as hydrogen source for the application of fuel cell power system

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ENERGY CONVERSION AND MANAGEMENT 2020年 213卷

作者： Yao, Jing Zhu, Pengfei Qian, Chenhui Hamidullah, Usamah Kurko, Sandra Yang, Fusheng Zhang, Zaoxiao Wu, Zhen Xi An Jiao Tong Univ Sch Chem Engn & Technol Xian 710049 Peoples R China Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Peoples R China Univ Belgrade Ctr Excellence Hydrogen & Renewable Energy Vinca Inst Nucl Sci Belgrade 11351 Serbia

This paper proposes a novel autothermal-equilibrium metal hydride reactor as the hydrogen source for the fuel cell power system, which employs phase change material (PCM) to recycle the hydrogen storage heat. A threedimensional model of the metal hydride reactor coupled with a salt hydrate PCM for heat recovery is developed. Based on the model, the effects of key operating and design parameters on the reactor are investigated for performance optimization, including operating pressure, melting temperature, latent heat and thermal conductivity of PCM. Through the parametric analysis, it is found that increasing the operating pressure is beneficial to accelerate the absorption reaction. The average reaction fraction at 2400 s is increased by 24% with the pressure increasing from 6 to 10 bar. The moderate melting temperature and the thermal conductivity of the PCM that is comparable to that of metal hydride bed contribute to the improvement of hydrogen storage efficiency. Using this kind of hydrogen source reactor in a fuel cell power system, stable hydrogen storage efficiency of approximately 60% in the experiment is presented. In addition, no obvious performance deterioration of the power system occurs after ten cycles.

关键词： Hydrogen storage Metal hydride reactor Fuel cell power system Heat recovery Autothermal equilibrium

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Net Unidirectional Fluid Transport in Locally Heated Nanochannel by Thermo-osmosis

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NANO LETTERS 2020年第12期20卷 8965-8971页

作者： Wang, Xin Liu, Maochang Jing, Dengwei Mohamad, Abdulmajeed Prezhdo, Oleg Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Peoples R China Univ Calgary Schulich Sch Engn CEERE Calgary AB T2N 1N4 Canada Univ Southern Calif Dept Chem Los Angeles CA 90089 USA

Thermo-osmosis driven by temperature gradients generally requires two liquid reservoirs at different temperatures connected by porous bodies or capillaries. We demonstrate, by molecular dynamics simulation, a new phenomenon toward nanoscale thermo-osmosis. Upon heating at a certain region of a nanochannel, multiple nanoscale convective layers are formed and can be manipulated to generate a net fluid transport from one reservoir to another, even without a temperature difference between them. A net unidirectional fluid transport with different rates can be achieved by precisely controlling location of the heated region. The net fluid transport can be enhanced further by tuning liquid-wall interactions. The demonstrated phenomenon provides a strategy for enhancing fluid mixing, which is often inefficient in nanoscale flows. Our finding is promising for chip-level cooling. The heat generated by chips can be employed to produce asymmetric temperature gradients in channels through proper configuration. Coolant liquids can thus be circulated without extra pumps.

关键词： thereto-osmosis interfacial flow nanofluidics molecular dynamics

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Two dimensional temperature measurement characteristics in pulverized coal combustion field by computed tomography-tunable diode laser absorption spectroscopy

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APPLIED THERMAL engineering 2020年 171卷

作者： Wang, Zhenzhen Kamimoto, Takahiro Deguchi, Yoshihiro Zhou, Wangzheng Yan, Junjie Tainaka, Kazuki Tanno, Kenji Watanabe, Hiroaki Kurose, Ryoichi Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Peoples R China Tokushima Univ Grad Sch Adv Technol & Sci 2-1 Minamijyosanjima Tokushima 7708501 Japan Cent Res Inst Elect Power Ind Yokosuka Kanagawa 2400196 Japan Kyushu Univ Fukuoka 8190395 Japan Kyoto Univ Kyoto 6158540 Japan

Two dimensional temperature and concentration distributions are important parameters for pulverized coal combustion used for power plant to understand the combustion field and develop the high efficient combustion technologies. However, it is difficult to measure two dimensional temperature and concentration in pulverized coal combustion field using conventional measurement technologies because pulverized coal combustion produces lots of dust and strong emission from its flame. This paper focused on the application of two dimensional temperature measurement method based on the combination of computed tomography and tunable diode laser absorption spectroscopy using absorption spectra of water vapor at 1388 nm and 1343 nm for each laser scanning using direct absorption spectroscopy, which show the better characteristics of spatial-temporal resolution, fast response, high sensitivity, self-calibration and optical accessibility. Accuracy of temperature measurement using tunable diode laser absorption spectroscopy was improved by applying the corrected spectroscopic database. Computed tomography reconstruction accuracy of 16 laser-paths configuration was evaluated using sum of squared difference (0.001) and zero-mean normalized cross-correlation (over 0.991), which presented the consistent temperature between assumed and reconstructed distributions. This developed computed tomography-tunable diode laser absorption spectroscopy was successfully applied to pulverized coal flame for two dimensional temperature measurement with 1 ms temporal resolution for time-series two dimensional temperature measurement in the range of 300-2500 K. The rationality was demonstrated by comparison of pulverized coal flame and Methane-Air flame temperature distributions due to the main heat release produced by methane fuel. Its applicability to pulverized coal combustion field will be benefit for optimal operation control and combustion efficiency improvement by combustion organization or new

关键词： Pulverized coal combustion power plant Two dimensional temperature measurement Tunable diode laser absorption spectroscopy (TDLAS) Computed tomography (CT)

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Thermal and film dynamics of multi-nozzle flash spray cooling towards large area and non-uniform heat source

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THERMAL SCIENCE AND engineering PROGRESS 2025年 63卷

作者： Lin, Xiang-Wei Wang, Xu-Dong Zhou, Zhi-Fu Zhu, Dong-Qing Xu, Wen-Wei Zhu, Hai Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Peoples R China Huawei Technol Co Ltd Shenzhen Peoples R China

Thermal management poses a crucial challenge to the operational reliability of high-power devices which characterized by large area and uneven heat sources. Flash spray, as one of the start-of-the-art technologies, satisfies the requirements of rapid heat removal and superior droplet breakup effects. This study aims to investigate the liquid dynamics and heat transfer characteristics of multi-nozzle flash spray on a non-uniform heat flux surface. Here, the Euler-Lagrangian method is coupled to account for the gas-droplet interactions, and the Lagrangian wall-film is applied to describe the liquid film evolution. The effects of spray height and nozzle number are systematically discussed in terms of velocity, liquid film thickness, average surface temperature, and temperature non-uniformity. Results reveal that the enhanced spray-to-spray interaction can greatly alter liquid film distribution, which in turn affects the heat transfer efficiency. Notably, while increasing spray coverage improves thermal contact area, it exhibits a non-linear relationship with temperature reduction, showing an optimal spray height and nozzle number for minimizing average temperature and temperature nonuniformity. The main contribution of present work lies in its in-depth analysis of multi-nozzle flash spray on large area and uneven heating surface, which is prevalent in industrial applications buy underexplored in prior works. These findings are expected to offer actionable guidelines for understanding complex spray cooling mechanisms and designing efficient thermal management systems.

关键词： Flash spray cooling Multi-nozzle array Liquid film dynamics Heat transfer characteristics Surface temperature uniformity

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Ultra-small TiO₂ nanoparticles embedded in carbon nanosheets for high-performance sodium storage

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CHEMICAL engineering JOURNAL 2021年 417卷

作者： Diao, Zhidan Wang, Yiqing Zhao, Daming Zhang, Xiaoping Mao, Samuel S. Shen, Shaohua Xi An Jiao Tong Univ Int Res Ctr Renewable Energy State Key Lab Multiphase Flow Power Engn Xian 710049 Shaanxi Peoples R China Univ Calif Berkeley Dept Mech Engn Berkeley CA 94720 USA

With the properties of high theoretical capacity and excellent structural stability, TiO2 has been widely studied as anode material for sodium-ion batteries (SIBs). In this work, a composite structure of ultra-small TiO2 nanoparticles embedded in carbon nanosheets (TCNS) is obtained by annealing polyvinylpyrrolidone coated Zn-Ti layered double hydroxide under inert atmosphere, with zinc species removed by hydrochloric acid. As sodium-ion battery anode, the resultant TCNS shows a high reversible capacity of 271.2 mAh g(-1) at 50 mA g(-1) and considerable cycling stability (maintaining 196.7 mAh g(-1) after 2000 cycles at 2 A g(-1)). Ex-situ XRD and TEM investigations clearly illustrate the structure changes of anatase during the sodium storage process. Specifically, ultra-small TiO2 nanoparticles in TCNS show obvious crystal distortion as triggered by the initial insertion of sodium ions, with the reversible sodium storage happening at the (101) active plane of anatase. As experimentally and theoretically evidenced, the twisted crystal structure is maintained in the subsequent cycles, which can effectively promote the sodium diffusion rate in anatase, resulting in the excellent rate and cycle performances of TCNS anode. This study provides informative guidance to explore high-performance TiO2 anodes for SIBs, with novel insights into the sodium ion insertion/extraction mechanism comprehensively elucidated during reversible sodium storage process.

关键词： TiO2 nanoparticles Anatase Sodium storage Crystal distortion Sodium diffusion kinetics

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