Effect of bipolar-plates design on corrosion,mass and heat transfer in proton-exchange membrane fuel cells and water electrolyzers:A review

Attaining a decarbonized and sustainable energy system,which is the core solution to global energy issues,is accessible through the development of hydrogen energy.Proton-exchange membrane water electrolyzers(PEMWEs)are promising devices for hydrogen production,given their high efficiency,rapid responsiveness,and compactness.Bipolar plates account for a relatively high percentage of the total cost and weight compared with other components of PEMWEs.Thus,optimization of their design may accelerate the promotion of PEMWEs.This paper reviews the advances in materials and flow-field design for bipolar plates.First,the working conditions of proton-exchange membrane fuel cells(PEMFCs)and PEMWEs are compared,including reaction direction,operating temperature,pressure,input/output,and potential.Then,the current research status of bipolar-plate substrates and surface coatings is summarized,and some typical channel-rib flow fields and porous flow fields are presented.Furthermore,the effects of materials on mass and heat transfer and the possibility of reducing corrosion by improving the flow field structure are explored.Finally,this review discusses the potential directions of the development of bipolar-plate design,including material fabrication,flow-field geometry optimization using threedimensional printing,and surface-coating composition optimization based on computational materials science.

Convective heat transfer of water flow in intersected rock fractures for enhanced geothermal extraction

Numerous intersected rock fractures constitute the fracture network in enhanced geothermal systems.The complicated convective heat transfer behavior in intersected fractures is critical to the heat recovery in fractured geothermal reservoirs.A series of three-dimensional intersected fracture models is constructed to perform the flow-through heat transfer simulations.The geometry effects of dead-end fractures(DEFs)on the heat transfer are evaluated in terms of intersected angles,apertures,lengths,and the connectivity.The results indicate that annular streamlines appear in the rough DEF and cause an ellipse distribution of the cold front.Compared to plate DEFs,the fluid flow in the rough DEF enhances the heat transfer.Both the increment of outlet water temperatureΔToutand the ratio of heat production Qrpresent the largest at the intersected angle of 90°while decline with the decrease of the intersected angle between the main flow fracture(MFF)and the DEFs.The extension of the length of intersected DEFs is beneficial to heat production while enhancing its aperture is not needed.Solely increasing the number of intersected DEFs induces a little increase of heat extraction,and more significant heat production can be obtained through connecting these DEFs with the MFF forming the flow network.

Forced Convection Boiling Heat Transfer and Dryout Characteristics in Helical Coiled Tubes with Various Axial Angles

对水和水蒸汽汽液两相流体在螺旋轴呈各种倾角放置的螺旋管内强制对流沸腾传热与烧毁特性进行了系统地试验研究，试验中系统及结构参数范围如下：压力：Ｐ＝０．４～３．０ＭＰａ质量流速：Ｇ＝１００～２４００ｋｇ／ｍ２·ｓ进口水温：Ｔ＝３０～８０℃出口干度：ｘ＝－０．０５～１．２管内壁面热负荷：ｑ＝０～５４０ｋＥ／ｍ２试验段结构参数：总长Ｌ＝６４４８ｍｍ，管内径ｄ＝１１ｍｍ，螺旋直径Ｄ＝２５６ｍｍ，螺旋升角β＝４．２７°螺旋管轴向放置倾角：水平位置（０°）、向上倾斜４５°（＋４５°）、垂直向上（＋９０°）、向下倾斜４５°（－４５°）．共进行了１０５０个工况的试验．试验结果表明，螺旋管内汽液两相流强制对流沸腾传热可以划分为核态沸腾区、两相流强制对流区、烧毁及烧毁后传热区等３种区域．通过数据处理和分析总结，给出了３区域间转变的边界方程，和３个区域内两相流传热系数的计算公式．根据试验观察和数据结果，对烧毁现象及烧毁点或区域发生的条件及机理进行了深入的分析研究，发现一系列有关现象的规律和特点，指出了其主要影响因素，并给出了烧毁点临界质量干度的预报公式．

Experiments and sensitivity analyses for heat transfer in a meter-scale regularly fractured granite model with water flow

Experiments of saturated water flow and heat transfer were conducted for a meter-scale model of regularly fractured granite. The fractured rock model （height 1502.5 ram, width 904 mm, and thickness 300 mm）, embedded with two vertical and two horizontal fractures of pre-set apertures, was constructed using 18 pieces of intact granite. The granite was taken from a site currently being investigated for a high-level nuclear waste repository in China. The experiments involved different heat source temperatures and vertical water fluxes in the embedded fractures either open or filled with sand. A finite difference scheme and computer code for calculation of water flow and heat transfer in regularly fractured rocks was developed, verified against both the experimental data and calculations from the TOUGH2 code, and employed for parametric sensitivity analyses. The experiments revealed that, among other things, the temperature distribution was influenced by water flow in the fractures, especially the water flow in the vertical fracture adjacent to the heat source, and that the heat conduction between the neighboring rock blocks in the model with sand-filled fractures was enhanced by the sand, with larger range of influence of the heat source and longer time for approaching asymptotic steady-state than those of the model with open fractures. The temperatures from the experiments were in general slightly smaller than those from the numerical calculations, probably due to the fact that a certain amount of outward heat transfer at the model perimeter was unavoidable in the experiments. The parametric sensitivity analyses indicated that the tem- perature distribution was highly sensitive to water flow in the fractures, and the water temperature in the vertical fracture adjacent to the heat source was rather insensitive to water flow in other fractures.

Numerical Study on Application of CuO-Water Nanofluid in Automotive Diesel Engine Radiator

Application of CuO-water nanofluid with size of the nanoparticles of 20 nm and volume concentrations up 2% is numerically investigated in a radiator of Chevrolet Suburban diesel engine under turbulent flow conditions. The heat transfer relations between airflow and nanofluid coolant have been obtained to evaluate local convective and overall heat transfer coefficients and also pumping power for nanofluid flowing in the radiator with a given heat exchange capacity. In the present study, the effects of the automotive speed and Reynolds number of the nanofluid in the different volume concentrations on the radiator performance are also investigated. The results show that for CuO-water nanofluid at 2% volume concentration circulating through the flat tubes with Renf = 6000 while the automotive speed is 70 km/hr, the overall heat transfer coefficient and pumping power are approximately 10% and 23.8% more than that of base fluid for given conditions, respectively.

Natural Convective Heat and Mass Transfer on a Vertical Heated Plate for Water Flow Containing Metal Corrosion Particles

Corrosion products of structural materials when contained in water usually are in two states:soluble state and colloidal particles with diameter about 10^(-3)—10^(-1)μm.Deposits of such corrosion products on tube surfaces under high pressure will jeopardize the operating economy of power plant equipment and even result in accidents. A numerical study is reported in this paper of the natural convective heat and mass transfer on a vertical heated plate subject to the first or mixed kind of boundary conditions for high-pressure water(P=17MPa)containing metal corrosion products with consideration of variable thermophysical properties.

考虑流体相变效应的粗糙裂隙非线性渗流换热机理

三维粗糙裂隙渗流换热机理的研究,对提升地下热储层的热提取率意义重大。当前,热开采过程中的多场耦合问题已取得了丰富的成果,但热开采过程中流体的相变作用对裂隙渗流特性及传热变化的影响却鲜有涉及。为剖析流体相变作用下的非线性渗流换热机理,以三维粗糙裂隙为研究对象,基于Fluent软件建立单相与多相流-热耦合模型,对比是否考虑相变作用的不同入口流速、入口温度和壁面温度时的局部换热系数分布特征。结果表明未考虑相变作用时,壁面局部粗糙程度控制局部换热系数的分布特征;基于Forchheimer公式,得知流体传热过程中非线性渗流特性显著。考虑相变作用后,流体呈现类似剪切稀释流体的特征,而气相体积分数则对系统换热过程起主导作用。因此,考虑流体的相变效应可以更准确地揭示热开采过程中的渗流特征和热提取效率的演化机理。

地热储层岩体粗糙裂隙的热流耦合效应研究

为了解决地热开采涉及复杂的多物理场耦合问题,提高开采效率,本文针对开采过程中的渗流-传热问题以离散元软件3DEC构建岩体粗糙裂隙热-流耦合数值模型。考虑不同三维形貌特征的岩体裂隙,模拟水力开度为19.17μm在不同流速时的水-岩温度变化规律。结果表明:由于裂隙形貌的阻滞作用,粗糙面出水口温度下降较慢,出水口温度有所上升,模型达到稳态所需的时间随流速和对流换热系数的增大而减小。裂隙形貌对流体和岩体温度分布均有影响,粗糙裂隙面的冷锋形态和裂隙面的形貌密切相关。光滑裂隙热突破快于粗糙裂隙,增加裂隙面的粗糙度有助于延长热突破时间。粗糙裂隙面相对于光滑裂隙面的总热量提取率略有提升,流速和对流换热系数的增加显著提高总热量提取率。通过本文研究可以为地热能系统的设计提供重要参数和指导,能够提高地热能开发利用效率。

汽轮发电机带有交替径向风道的转子流体与传热耦合分析

针对汽轮发电机带有交替径向通风道的转子发热冷却问题,以一台350 MW水氢氢冷汽轮发电机为研究对象,依据流体力学和传热学的基本理论,首先建立计及旋转的电机全域通风网络模型,采用逐次迭代法计算得到各支路流量和节点压力。其次,建立了带有交替径向风道的发电机转子流体-传热三维物理模型和数学模型,给出了基本假设和相应的边界条件,同时将通风网络计算得到的风速和压力作为转子求解域的耦合边界,采用有限体积法进行求解,计算结果与实测值吻合。然后分析了交替径向风道内流量分配和氢气流动情况,研究了转子内部氢气温度分布和槽楔出风口风温变化规律,探明了转子绕组和铁心轴向温度分布特性,讨论了副槽入口流量和槽楔出口直径对转子流体和温度的影响。得出副槽入口流量应控制在0.1~0.16 m^(3)/s范围内,且选择较小的槽楔出口直径,可以提高通风系统的效率与风量分配均匀性,降低转子轴向热不平衡。

INVESTIGATION ON FLOW AND HEAT TRANSFER CHARACTERISTICS OF ANNULAR TWO-PHASE FLOW THROUGH THE VENTURITUBE

A model that incorporates the important phenomena in annular gas-water flow through a Venturi tube has been presented. A series of the experiments were carried out to measure the flow and heat transfer characteristics in cold and hog conditions. The comparison between numerical and experimental results shows good agreement.

Friction factor and heat transfer of nanofluid in the turbulent flow through a 90°bend

Heat transfer and energy performance of Al_(2)O_(3)/water nanofluid in a 90°bend with circular cross-section are investigated in the range of Reynolds number(Re)from 5000 to 30000,particle volume concentration(Φ)from 0.005%to 4%,Schmidt number(Sc)from 9870 to 296100,Dean number(De)from 6636 to 14847.The momentum and energy equations of nanofluid together with the dynamic equation for nanoparticles are solved numerically with the particle convection,diffusion,coagulation and breakage taken into consideration.Some results are validated by comparing with the available experimental or numerical results.The effect of Re,Φ,Sc and De on the friction factor and heat transfer of Al_(2)O_(3)/water nanofluidis discussed.The results showed that the particle number decreases along the pipeline.Increasing De,Sc leads to a decrease and increase ofΦ,respectively.The mean particle diameter and particle polydispersity increase with increasing Debut with decreasing Sc.The friction factor increases with increasingΦ,Sc De and Pr but with decreasing Sc.The ratio of energy performance evaluation criterion(PEC)for the Al_(2)O_(3)/water nanofluid to the base fluid increases with increasing Re,Φand De,but with decreasing Sc.Finally,the expression of ratio of energy PEC for the nanofluid to the base fluid as a function of Re,Φ,Sc and De is derived.

Numerical investigation of flow unsteadiness and heat transfer on suction surface of rotating airfoils within a gas turbine cascade

The effects of the periodical turbulence and pressure fluctuation on suction surface heat transfer over airfoils of a row of rotor blades with a certain type have been investigated numerically in this paper.The calculation is perfomed using v^(2)-f model with the numerical results of pressure fluctuation and heat transfer performance over 4 sample points being analyzed and compared with existing experimental data.It shows that the static pressure change has significant impact on heat transfer performance of the fore suction surface,especially in the active region of the shock waves formed from the trailing edge of upstream nuzzles.While,for the rear suction surface,the flow turbulence contributes more to the heat transfer change over the surface,due to the reduced pressure oscillation through this region.Phase shifted phenomenon across the surface can be observed for both pressure and heat transfer parameters,which should be a result of turbulence migration and wake passing across the airfoil.

浅层地热开采中砂岩单裂隙渗流传热试验研究

浅层地热能的开发利用关系着“双碳”目标的顺利达成,其中目标储层岩石裂隙渗流传热特性的研究对地下水源热泵系统的成效至关重要。但以往的裂隙渗流传热研究多是考虑粗糙面、流速、围压、温度等单一因素对其传热效率的评价,并未系统探究多级流速下浅层地热储层(围压和岩石温度)变化对渗流传热演化规律的认识及其贡献程度的对比。因此,文章基于课题组自主研发的裂隙岩石渗流传热试验系统,开展了多级流速下的砂岩单裂隙渗流传热试验,分析了单裂隙渗流传热在多级流速下的全过程演化特性,探讨了浅层地热中的敏感性参数(围压和岩石温度)对渗流传热的影响规律及其贡献程度。试验结果发现:(1)出口水温和对流换热系数随水流流速的增大,其变化趋势有明显的阶段性转折;(2)围压的增大导致裂隙开度减小,流动边界层变薄,而温度梯度的增大将引起热流密度的上升,都将导致出口水温和对流换热系数呈现上升趋势;(3)岩石温度的贡献程度明显高于围压,特别是从60℃增大至70℃时,对流换热系数有了大幅度增长。

气侧均流装置对冷却三角单元流动传热特性影响的实验研究

对于间接空冷系统冷端基本传热元件−冷却三角单元,通过在其加装及相邻未加装气侧均流装置冷却三角单元内的两侧冷却柱沿散热管束横向布置风速、风温、壁温测点,进一步在左右两侧出水柱布置壁温测点,对比分析两侧冷却柱沿散热管束横向迎风风速、风温、壁温及出水壁温的变化规律,研究气侧均流装置对冷却三角单元流动传热特性及出水壁温分布的影响机制。研究结果表明:加装气侧均流装置后冷却三角单元两侧冷却柱沿散热管束横向迎风风温、壁温分布更加均匀,两侧出水柱壁温均值更低,且降低了两侧出水柱壁温差,气侧均流装置优化了两侧冷却柱的换热均匀性。

液态金属快堆螺旋管蒸汽发生器一、二次侧耦合传热数值研究

螺旋管蒸汽发生器是液态金属快堆中能量传递的核心设备,其运行的稳定性、安全性对核电站的运行有至关重要的影响。为此,本文构建了液态金属快堆螺旋管蒸汽发生器一次侧、二次侧耦合传热的三维数值模型,分别基于经济合作与发展组织核能署(The Organisation for Economic Co-operation and Development,OECD/NEA)物性手册和美国国家标准与技术研究院(National Institute of Standards and Technology,NIST)数据库建立液态金属和水-水蒸气变物性计算关联式,采用Lee相变模型计算二次侧水-水蒸气蒸发过程中两相间的质量传递。基于实验数据,分别对本文模型一次侧传热以及二次侧传热的计算可靠性进行了验证。最后以铅铋快堆为例,研究了不同一次侧进口参数下蒸汽发生器一、二次侧之间的耦合传热特性,并与传统水冷堆进行了对比。结果表明:在同等条件下,相比于传统水冷堆,一次侧采用铅铋液态金属时,一、二次侧之间的壁面热流密度明显提升,热流密度峰值可达1439.97 kW·m^(-2),比水冷堆相应数值提升5~6倍,这导致二次侧管内气相蒸发过程明显加剧,体积含气率急剧上升;同时,一、二次侧之间的沿程热流密度分布更加不均匀,沿程热流密度分布相对偏差值比水冷堆相应数值增大3~4倍。随着一次侧进口铅铋温度从350℃增大到450℃,一、二次侧之间的壁面热流密度随之增大,对应的热流密度峰值从950.7 kW·m^(-2)增大到1439.97 kW·m^(-2),提升约1.5倍,同时一、二次侧之间的沿程热流密度分布更加不均匀,不均匀度增大20%。

英山地热田区深大断裂的控水控热作用及地热系统成因研究

目前对英山地区深部地温场的分布情况以及构造控热模式尚无系统研究,不利于地热资源科学的开发利用。基于野外裂隙测量、浅层连续测温、钻孔压水试验等成果,建立了英山裂隙岩体地下水渗流-传热三维模型,对深部储层在不同构造组合模式下的压力场、温度场和达西流速场进行分析。研究结果表明:研究区深部温度场和压力场受断裂系统影响较大,在致密基岩及隔水断层处,流体运动微弱,热量运移以热传导为主,导水断层处以热对流为主;在深部导水断层区域温度和水压偏低,与导水断层处相比,隔水断层处水压偏高;在2 000 m深度以深,高温区和水力交换强烈区与导水断层带处完全对应,表明断层是储层中最主要的流体和热量运移通道;区内断层组合模式为复合模式,北东向断层为英山地区主要导水导热构造,热水在沿北东向断层向上运移的过程中,受南北向断层的阻隔,最终在两组断层的交叉复合位置处形成温泉。该研究可为研究区内的地热资源科学勘查和合理开发利用提供参考。

超临界工况下水在换热表面传热特性研究进展

对于超临界水传热特性的研究,自21世纪初以来呈快速增长的态势发展.该文总结了近年来国内外学者对于超临界水换热性能的研究,系统分析了浮升力、壁面热流密度、质量流速、压力等因素对其流动换热特性的影响.众多结果表明:浮升效应引起的剪切应力和径向流速的变化会导致传热恶化;通过减小热流密度,提高质量流速能有效改善传热.目前研究中给出了超临界水一般传热关系式,但其适用精度还需进一步提升.

某发动机冷却水套散热性能分析及优化

为准确评估发动机水套换热性能,基于AVL_FIRE软件对某发动机缸盖、缸体水套的流速、换热系数进行计算流体动力学(computational fluid dynamics,CFD)仿真分析。仿真结果表明:第4缸排气侧流速相对其他缸偏低,部分区域换热系数较小,无法满足评价标准;缸盖集成排气歧管后端法兰处冷却液流速较低,下层水套基本没有冷却液流动,为流动死区,容易使热负荷集中;冷却液体积流量为136 L/min时,发动机水套流阻为42 kPa,相对匹配功率为450 W的电子水泵,水套流阻较大。将第4缸气缸垫的一个水孔截面积增大80%,增设1个气缸垫水孔,另外一个水孔截面积减小10%,同时将堵棒流通长度增加150%,通过碗形塞优化排气歧管后端水套上、下层的连通,对优化水套进行CFD分析及流-固耦合分析,结果表明:冷却液体积流量为136 L/min时,水套流阻为35 kPa,满足匹配的电子水泵功率要求;优化后第4缸缸体下层水套冷却液流动明显改善,第2、3缸进排气门鼻梁区后端换热系数偏低,但缸盖水套关键区域温度满足限值要求。

EXPERIMENTAL STUDY OF ENHANCED HEAT TRANSFER BY FLOW-INDUCED VIBRATION OF ELASTIC TUBE BUNDLES

New concept of heat transfer enhancement by flow-induced vibration was put forward, and a novel heat transfer element called elastic tube bundles was designed. The experimental investigation was performed on its characteristics of flow-induced vibration in out-tube or in-tube flow. Under the conditions of fixed heat flux and steam-water heat transfer, the regularity of heat transfer enhancement by flow-induced vibration was examined.

Numerical Simulation of an Airfoil Electrothermal-Deicing-System in the Framework of a Coupled Moving-Boundary Method

A numerical method for the analysis of the electrothermal deicing system for an airfoil is developed taking into account mass and heat exchange at the moving boundary that separates the water film created due to droplet impingement and the ice accretion region.The method relies on a Eulerian approach(used to capture droplet dynamics)and an unsteady heat transfer model(specifically conceived for a multilayer electrothermal problem on the basis of the enthalpy theory and a phase-change correction approach).Through application of the continuous boundary condition for temperature and heat flux at the coupled movingboundary,several simulations of ice accretion,melting and shedding,runback water flow and refreezing phenomena during the electrothermal deicing process are conducted.Finally,the results are verified via comparison with experimental data.A rich set of data concerning the dynamic evolution of the distribution of surface temperature,water film height and ice shape is presented and critically discussed.