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Effects of baffle position in serpentine flow channel on the performance of proton exchange membrane fuel cells

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Chinese Journal of Chemical Engineering 2024年第5期69卷 250-262页

作者： Guodong Xia Xiaoya Zhang Dandan Ma MOE Key laboratory of Enhanced heat transfer and Energy Conservation Beijing Key Laboratory of Heat Transfer and Energy ConversionBeijing University of TechnologyBeijing 100124China

This study used a three-dimensional numerical model of a proton exchange membrane fuel cell with five types of channels:a smooth channel(Case 1);eight rectangular baffles were arranged in the upstream(Case 2),midstream(Case 3),downstream(Case 4),and the entire cathode flow channel(Case 5)to study the effects of baffle position on mass transport,power density,net power,***,the effects of back pressure and humidity on the voltage were *** showed that compared to smooth channels,the oxygen and water transport facilitation at the diffusion layer-channel interface were added 11.53%-20.60%and 7.81%-9.80%at 1.68 A·cm^(-2)by adding *** closer the baffles were to upstream,the higher the total oxygen flux,but the lower the flux uniformity the worse the water *** oxygen flux of upstream baffles was 8.14%higher than that of downstream baffles,but oxygen flux uniformity decreased by 18.96%at 1.68 A·cm^(-2).The order of water removal and voltage improvement was Case 4>Case 5>Case 3>Case 2>Case *** power of Case 4 was 9.87%higher than that of the smooth *** the Case 4,when the cell worked under low back pressure or high humidity,the voltage increments were *** potential increment for the back pressure of 0 atm was 0.9%higher than that of 2 atm(1 atm=101.325 kPa).The potential increment for the humidity of 100%was 7.89%higher than that of 50%.

关键词： Proton exchange membrane fuel cell Baffle position mass transfer Net power Uniformity Voltage increment

Numerical Study on heat transfer and Frictional Resistance of Two Types of Molten Salts in Straight Channels and Supercritical Carbon Dioxide in Airfoil Channels

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Journal of Thermal Science 2024年第4期33卷 1443-1457页

作者： WANG Yanquan LU Yuanwei GAO Qi LI Feng MA Yancheng WANG Yuanyuan WU Yuting MOE Key laboratory of Enhanced heat transfer and Energy Conservation Beijing Key Laboratory of Heat Transfer and Energy ConversionBeijing University of TechnologyBeijing100124China

Molten salt and supercritical carbon dioxide(sCO_(2))are considered to be one of the most promising combined heat transfer refrigerants for third-generation solar thermal power *** evaluate the potential of chloride salts and carbonates in third-generation solar thermal power generation,this paper uses molten salts and sCO_(2)as the working media of printed circuit board heat exchangers(PCHE),and uses numerical simulation to study the heat transfer and friction of PCHE channels with different molten salts and sCO_(2),and establishes predictive correlations respectively.A local heat transfer and friction study was conducted on the sCO_(2)side of the airfoil channel,and it was found that the inlet mass flow rate has a significant impact on it,while the inlet temperature has a relatively small impact.A comprehensive comparison was made between the heat transfer and friction of two molten salts,and the comprehensive performance of chloride salts was 70%-80%higher than that of *** results indicate that the potential of chloride salts in third-generation solar thermal power generation is much greater than that of carbonates.

关键词： third generation solar thermal power generation sCO_(2) PCHE molten salt

On the spreading behavior of a droplet on a circular cylinder using the lattice Boltzmann method

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Chinese Physics B 2024年第6期33卷 434-443页

作者：杨帆金虎戴梦瑶 School of Energy and Power Engineering University of Shanghai for Science and TechnologyShanghai 200093China Shanghai Key laboratory of Multiphase Flow and heat transfer in Power Engineering Shanghai 200093China

The study of a droplet spreading on a circular cylinder under gravity was carried out using the pseudo-potential lattice Boltzmann high-density ratios multiphase model with a non-ideal Peng–Robinson equation of state. The calculation results indicate that the motion of the droplet on the cylinder can be divided into three stages: spreading, sliding, and *** contact length and contact time of a droplet on a cylindrical surface can be affected by factors such as the wettability gradient of the cylindrical wall, the Bond number, and droplet size. Furthermore, phase diagrams showing the relationship between Bond number, cylinder wall wettability gradient, and contact time as well as maximum contact length for three different droplet sizes are given. A theoretical foundation for additional research into the heat and mass transfer process between the droplet and the cylinder can be established by comprehending the variable rules of maximum contact length and contact time.

关键词： lattice Boltzmann methods droplet circular cylinder wettability gradient

Combustion and Self-Desulfurization Characterization of Blended Low-Rank Coals for Improved Resource Utilization in Fluidized Bed Boilers

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Journal of Thermal Science 2024年第3期33卷 1242-1256页

作者： SU Lipeng ZHANG Cong ZHANG Yongsheng WANG Tao WANG Jiawei Key laboratory of Power Station Energy transfer Conversion and System Ministry of EducationNorth China Electric Power UniversityBeijing102206China

The co-combustion of low-rank coals through fluidized bed boiler(CFB)is an effective approach to enhance the level of resource *** date,there has been a lack of investigation concerning the co-combustion kinetics and self-desulfurization characteristics of coal slime,coal gangue,and raw *** this study,we adopted multiple model-free and model-fitting methods to comparatively analyze co-combustion kinetics of blended coals on the basis of thermogravimetric ***,the sulfur balance and self-desulfurization of blended coals in the co-combustion were intensively investigated using a tube furnace *** results reveal that in the presence of coal gangue in blended coals,the average activation energy(E_(a))falls within the range of 65.7 kJ/mol to 100.4 kJ/mol,as determined by four model-free ***,in the absence of coal gangue,only the Flynn-Wall-Ozawa(FWO)and Friedman(FM)methods are deemed appropriate for calculating the average E_(a),yielding a value of 77.3 kJ/*** first order reaction model is confirmed to be reliable for analyzing the co-combustion kinetics of low-rank blended *** of the specific composition of the blended coal,a significant linear correlation exists between the Ea and the natural logarithm of the pre-exponential factor(lnA)within an extensive range of ***,the addition of coal gangue to the blended coal substantially enhances the self-desulfurization level,resulting in an increase from 25.7%to60.7%at 1073 *** self-desulfurization efficiency exhibits a good linear relationship with both the mass ratio of coal gangue to coal slime and the molar ratio of calcium to *** a practical implementation,the optimal addition ratio of coal gangue is a trade-off between the self-desulfurization efficiency and the ignition capacity.

关键词： coal slime coal gangue fluidized bed boilers self-desulfurization resource utilization

Experimental investigation on the gravity driven discharge of cohesive particles from a silo with two outlets

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Particuology 2024年第6期89卷 11-21页

作者： Li Dai Zhulin Yuan Fengxian Fan Conghui Gu School of Energy and Power Engineering University of Shanghai for Science and TechnologyShanghai 200093China Key laboratory of Energy Thermal Conversion and Control of Ministry of Education School of Energy and EnvironmentSoutheast UniversityNanjing 210096China Shanghai Key laboratory of Multiphase Flow and heat transfer in Power Engineering University of Shanghai for Science and TechnologyShanghai 200093China School of Energy and Power Jiangsu University of Science and TechnologyZhenjiang 212100China

An experimental study on the gravity driven discharge of cohesive particles from a silo with two outlets was *** discharge behaviors under the conditions that a single outlet was open and two outlets were open were investigated by varying the moisture content of the particles and the filling height of the particles in the *** results show that the discharge rate of the cohesive particles increases gradually at the beginning,then almost keeps constant,and finally drops *** discharge rate in case of two openings is around 1.1–1.6 times that in case of a single *** filling height leads to lower discharge rate in case of a single opening but results in higher discharge rate in case of two ***,the avalanche dynamics in case of a single opening was examined,and the mixing behavior of the cohesive particles was *** is observed that the discharge flow is promoted by the avalanche phenomenon in the silo,generating a general trend that the normalized mass of discharge increases with the filling height at higher moisture *** case of a single opening,the transition from mass flow to funnel flow favors the particle mixing,resulting in an increasing mixing index as the moisture content *** general,a better performance of mixing can be achieved in case of a single opening compared with in case of two *** study provides vital information for fundamental understanding of the gravity driven discharge of cohesive particles from the silo with multiple outlets.

关键词： Cohesive particles Moisture content Discharge rate Avalanche Mixing

Field synergy principle of heat and mass transfer

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Chinese Science Bulletin 2009年第24期54卷 4604-4609页

作者： WU LiangBo LI Zhen SONG YaoZu Key laboratory of heat transfer and Energy Conversion of Beijing Municipality School of Aerospace Tsinghua University Beijing100084 China

Simultaneous heat and mass transfer widely exists in nature and engineering, and it is of vital importance to enhance heat and mass transfer efficiency. In this paper, field synergy equation of heat and mass transfer is derived from its energy equation. Results show that the total transferred heat (including the conducted heat and the heat transferred by mass diffusion through the heat transfer interface) is determined by the values of fluid velocity and enthalpy gradient as well as the value of synergy angle α of velocity vector and enthalpy gradient field. Decreasing the value of α enhances the heat and mass transfer. This means the higher the synergy of velocity vector and enthalpy gradient field, the higher the total transferred heat. By the synergy principle of heat and mass transfer, some methods may be developed to improve the heat and mass transfer efficiency.

关键词：传热传质增效流体速度协同效应传质效率能量方程梯度场矢量和

heat mass transfer model of fouling process of calcium carbonate on heat transfer surface

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Science China(Technological Sciences) 2008年第7期51卷 882-889页

作者： QUAN ZhenHua CHEN YongChang MA ChongFang Education Ministry Key laboratory of Enhanced heat transfer and Energy Conservation College of Environmental and Energy EngineeringBeijing University of TechnologyBeijing 100022China

A new heat mass transfer model was developed to predict the fouling process of calcium carbonate on heat transfer surface. The model took into account not only the crystallization fouling but also the particle fouling which was formed on the heat transfer surface by the suspension particles of calcium carbonate in the su- persaturated solution. Based on experimental results of the fouling process, the deposition and removal rates of the mixing fouling were expressed. Furthermore, the coupling effect of temperature with the fouling process was considered in the physics model. As a result the fouling resistance varying with time was obtained to describe the fouling process and the prediction was compared with experimental data under same conditions. The results showed that the present model could give a good prediction of fouling process, and the deviation was less than 15% of the experimental data in most cases. The new model is credible to predict the fouling process.

关键词： fouling calcium carbonate heat mass transfer model

Apically guiding electron/mass transfer reaction induced by Ag/FeN_(x)Mott-Schottky effect within a hollow star reactor toward high performance zinc-air batteries

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Journal of Energy Chemistry 2024年第8期95卷 106-116,I0004页

作者： Kaixiang Shi Kaixin Wang Tong Li Junhao Li Jie Ren Xu Li Yonggang Min Zhouguang Lu Wei Tan Quanbing Liu Guangdong Provincial laboratory of Chemistry and Fine Chemical Engineering Jieyang Center(Rongjiang laboratory) Guangdong University of TechnologyJieyang 515200GuangdongChina Guangzhou Key laboratory of Clean Transportation Energy Chemistry Guangdong Provincial Key Laboratory of Plant Resources BiorefinerySchool of Chemical Engineering and Light IndustryGuangdong University of TechnologyGuangzhou 510006GuangdongChina Key laboratory of Electrochemical Energy Storage and Energy Conversion of Hainan Province School of Chemistry and Chemical EngineeringHainan Normal UniversityHaikou 571158HainanChina School of Materials and Energy Guangdong University of TechnologyGuangzhou 510006GuangdongChina Department of Materials Science and Engineering Southern University of Science and TechnologyShenzhen 518055GuangdongChina

The disparity in the transfer of carriers(electrons/mass)during the reaction in zinc-air batteries(ZABs)results in sluggish kinetics of the oxygen reduction reaction(ORR)and oxygen evolution reaction(OER),along with elevated overpotentials,thereby imposing additional constraints on its ***,the pre-design and target-development of inexpensive,high-performance,and long-term stable bifunctional catalysts are urgently *** this work,an apically guiding dual-functional electrocatalyst(Ag-FeN_(x)-N-C)was prepared,in which a hierarchical porous nitrogen-doped carbon with three-dimensional(3D)hollow star-shaped structure is used as a substrate and high-conductivity Ag nanoparticles are coupled with iron nitride(FeN_(x))*** calculations indicate that the Mott-Schottky heterojunction as an inherent electric field comes from the two-phase bound of Ag and FeN_(x),of which electron accumulation in the FeN_(x)phase region and electron depletion in the Ag phase region promote orientated-guiding charge *** effective modulation of local electronic structures felicitously reforms the d-band electron-group distribution,and intellectually tunes the masstransfer reaction energy barriers for both ORR/***,the hollow star-s haped hierarchical porous structure provides an apical region for fast mass *** results show that the halfwave potential for ORR is 0.914 V,and the overpotential for OER is only 327 mV at 10 mA cm^(-2).A rechargeable ZAB with Ag-FeN_(x)-N-C as the air cathode demonstrates long-term cycling performance exceeding 1500 cycles(500 h),with a power density of 180 mW cm^(-2).Moreover,when employing AgFeN_(x)-N-C as the air cathode,flexible ZABs demonstrate a notable open-circuit voltage of 1.42 V and achieve a maximum power density of 65.6 mW cm^(-2).Ag-FeN_(x)-N-C shows guiding electron/mass transfer route and apical reaction microenvironment for the electrocatalyst architecture in the explo

关键词： Hollow star structure Mott-Schottky effect Apically guiding effect Bifunctional catalysis Zinc-air batteries

Advances in the kinetics of heat and mass transfer in near-continuous complex flows

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Frontiers of physics 2024年第4期19卷 187-234页

作者：许爱国张德佳甘延标 National Key laboratory of Computational Physics Institute of Applied Physics and Computational MathematicsP.O.Box 8009-26Beijing 100088China State Key laboratory of Explosion Science and Technology Beijing Institute of TechnologyBeijing 100081China HEDPS Center for Applied Physics and Technologyand College of EngineeringPeking UniversityBeijing 100871China State Key laboratory for GeoMechanics and Deep Underground Engineering China University of Mining and TechnologyBeijing 100083China National Key laboratory of Shock Wave and Detonation Physics Mianyang 621999China Hebei Key laboratory of Trans-Media Aerial Underwater Vehicle School of Liberal Arts and SciencesNorth China Institute of Aerospace EngineeringLangfang 065000China

The study of macro continuous flow has a long ***,the exploration of heat and mass transfer in small systems with a particle number of several hundred or less has gained significant interest in the fields of statistical physics and nonlinear ***,due to absence of suitable methods,the understanding of mesoscale behavior situated between the aforementioned two scenarios,which challenges the physical function of traditional continuous fluid theory and exceeds the simulation capability of microscopic molecular dynamics method,remains considerably *** greatly restricts the evaluation of effects of mesoscale behavior and impedes the development of corresponding regulation *** access the mesoscale behaviors,there are two ways:from large to small and from small to *** the necessity to interface with the prevailing macroscopic continuous modeling currently used in the mechanical engineering community,our study of mesoscale behavior begins from the side closer to the macroscopic continuum,that is from large to *** on some fundamental challenges encountered in modeling and analysis of near-continuous flows,we review the research progress of discrete Boltzmann method(DBM).The ideas and schemes of DBM in coarse-grained modeling and complex physical field analysis are *** relationships,particularly the differences,between DBM and traditional fluid modeling as well as other kinetic methods are *** verification and validation of the method,some applied researches including the development of various physical functions associated with discrete and non-equilibrium effects are *** directions of DBM related studies are indicated.

关键词： near-continuous flow non-equilibrium kinetics discrete Boltzmann method complex physical field analysis