【作者】 刘坤；

【导师】 肖金生； 明平顺；

【作者基本信息】 武汉理工大学 ， 动力机械及工程， 2008， 博士

【摘要】 质子交换膜燃料电池是一个多物理场、多相、多尺度的动态复杂系统。工作中,反应气体从流道到反应区经历了电堆(米级)、流道(毫米级)、扩散层(微米级)和催化层及膜(纳米级)的多尺度变化,而目前的研究并没有充分揭示质子交换膜燃料电池中的传递现象及其机理。通过对燃料电池进行计算机模拟,能最大限度的揭示燃料电池内部的工作机理及工作状态,进而对燃料电池结构进行优化设计,以降低实验成本,提高电池性能。本文研究了流道结构对电池性能的影响。考虑电池的综合性能,流道尺寸存在一个最优值,在本设计中深度为0.5mm时最好;电池运行时低电流密度下,流道宽与岸宽比越小,电池性能越好,高电流密度时情况正好相反;流道宽度与岸宽之比为1:1时,电池的综合性能最好。在综合考虑电池性能和结构强度时,半圆形的截面流道最好;随着壁面接触角增大(疏水性的增强),排水时间减小,但在壁面接触角到达90°后,减小的幅度减小。对PEM燃料电池扩散层的孔隙率变化、亲疏水性以及厚度进行了深入研究。结果表明:对于均一孔隙率结构的扩散层,增加孔隙率和接触角,减少厚度时,有利于扩散层内的排水和导气;孔隙率梯度变化的扩散层更有利于液态水的排出;平面内孔隙率间隔分布的扩散层有利于气、水的传输,能提高电池的性能。研究了PEM燃料电池膜中水传递的主要影响因素。结果表明:提高运行温度,减小质子交换膜厚度,加大阴极侧空气的过量系数,增大阴阳极气体的相对湿度、操作压力和电流密度,膜中的水含量都会增加,有助于提高电池性能。分析了影响电堆气体分配均匀性的主要因素。结果表明:减小进气的速度,增加进气的压力,可以提高电堆气体分配的均匀性。但同时小的进气的速度会带来水管理的问题,大的进气压力会增加电池的寄生功率;电堆阴极单进口进气时,U形进气方案要优于Z形进气方案;电堆阴极双入口进气时采用两端双入口进气最佳;增大电堆总管截面积或采用变截面总管可以有效的提高电堆中各单电池气体分配的均匀性;回收反应中的汽化水产生的废热能提高电堆的性能。综上所述,本文从多尺度角度,通过对电池中水气的传输以及堆中反应气的分配模拟,对PEMFC进行了从微观到介观,再到宏观的系统分析,从而得出有意义的成果,以加强对电池原理的深入研究,从而促进燃料电池性能的提高。更多还原

【Abstract】 PEMFC(Proton Exchange Membrane Fuel Cell) is a complex dynamic system of multi-physics fields,multi-phase and multi-scale.Reaction gas flows from channel to reaction zone in operation condition,and scales change from stack(meter class),to channel(millimeter class),GDL(Gas Diffusion Layer)(micron class) and catalyst layer(nano-meter class).Phenomenon and mechanism of transportation in PEMFC have not been studied thoroughly in recent research.Modeling of PEMFC using software can show the working conditions inside the PEMFC and reveal the mechanism.With structure optimization,the performance of PEMFC can be improved and the cost can be reduced.Influence of channel structure on performance of PEMFC has been studied. PEMFC operates at the best performance when the depth of channel is 0.5mm.Under low current density condition,performance improves with the decrease of ratio of width of channel to the width of shore.Road to the structure of the convection cell performance impact was studied.Condition under high current density is quite the contrary.The total performance reach peak when the width of channel equals the width of shore.As for the cross-section of channel,PEMFC has the best performance and structural intensity with cross-section of semicircle.Time of water drain out of the channel decreases with the increase of contact angle(improvement of hydropholic characteristic),and decreases little when contact angle reaches 90°.Porosity,hydrophilic and hydropholic characteristics and thickness of GDL are studied.Results show that it’s better for the transfer of gas and water with the increase of porosity and decrease of contact angle and thickness when the porosity is uniform.And the gradient change in porosity is better for the transfer of liquid water. GDL with porosity spacing distribution in plane is better for the transfer of gas and water,so can improve the performance of PEMFC.The main factors influence the water transfer in the membrane of PEMFC is studied.Water content in membrane and performance of PEMFC increase with the increase of temperature,stoichiometry of air,relative humidity of react gas,operation pressure and current density,decrease of thickness of membrane.Main factors affect gas distribution in stack is studied.Results show that gas distributes even with low inlet velocity and high inlet pressure.At the meanwhile,low inlet velocity will cause problem of water drainage and high inlet pressure will cause problem of more accessory power.U-type is better than Z-type under condition of single inlet in cathode.And two inlets at the ends of cathode have the best PEMFC performance.Gas distributes even with increase of area of cross-section of main inlet or using variable cross-section.Reuse of the waste heat produce in water can also improve the performance of PEMFC.In summarization,study of PEMFC is made from micro scale to macro scale. Transfer of water in channel and gas distribution in stack is studied with the combination of micro structure of channel and macro structure of stack,which is the coupling of multi-scale.Results of study are useful for insight understanding of mechanism of PEMFC and improving of performance of PEMFC.更多还原