The Study Of Water Management For Straight-parallel Flow Field Of Proton Exchange Membrane Fuel Cell

Water management is a persistent challenge for polymer electrolyte membrane(PEM)fuel cells with perfluorosulfonic acid(PFSA)type membranes,which require high water activity for suitable ionic conductivity.Humidification of reactant gases ensures proper humidification of the membrane.Consequently,much of the water produced by the oxygen reduction reaction at the cathode is generated in liquid form.Liquid water invades the pores of the catalyst layer and gas diffusion layer and restricts diffusion of oxygen to the catalyst.The liquid water emerges from the GDL via capillary action,accumulates in gas channels,covers the GDL surface,increases the pressure differentials along flow field channels,and creates flow maldistribution and instability in flow field with multiple parallel channels,then the output performance of fuel cells degrade.So it is necessary to study the water management on flow field.As one of traditional PEMFC flow fields,Straight-parallel flow field have many advantages,such as simple structure,easy fabrication,and create the lowest pressure drop between the traditional the gas-distributor plane of proton exchange membrane fuel cells(PEMFC),but it also gives rise to the problem of severe flow distribution in the flow field.As a consequence,the mass transfer and electrochemistry reaction for the PEMFCs flow field in insufficient process significantly influence the output power of fuel cells,and it is necessary to optimize the geometric construction of parallel flow field to obtain a better flow distribution.In this dissertation,an analytical method based on mass and momentum conservation is proposed to numerical optimization for the flow field of fuel cells,and the results release from this solution is validated by computing from the three-dimensional computational fluid dynamics simulations,CFD.the optimization results can eliminate the misdistribution,and an even flow distribution can be achieved.Then reasearching the effect of various velocity and wall wettabillty on liquid droplet moving in the gas channel via CFD code base on VOF numerical model.Finally,Proton exchange membrane fuel cells(PEMFCs)with transparent windows are used for visualizing the two-phase flow in the channels,and the effect of different operations and liquid droplet on the output performance of fuel cell will be studied in this experiment.The main research results as follow.1.This dissertation obtained by analyzing the flow field numerical study of the total import and export flow channel and side channel depth and width smaller increase the export total circulation of the flow channel cross section and side of the flow channel cross section larger than,the pressure drop causes the flow field,the flow channel uniformity and more uniform distribution of mass.And by analytical method optimized with CFD flow field numerical simulation results of this momentum and mass conservation equations based on the analytical method for parallel flow field structure size optimization is effective.2.The liquid flow channel the flow characteristics and the external operating conditions are closely related,the reaction gas flow passage bigger and more conducive to the flow path of the liquid water exclusion,and vice versa when the flow channel flow is not only smaller but also not conducive to the flow channel drain plug flow Road thereby affecting the flow channel during the reaction mass and performance output.While the hydrophilic and hydrophobic flow channel favor drain diffusion layer.3.Reaction gas flow rate,the operating pressure of the reaction gas in the reaction gas humidification temperature increase under certain conditions the performance of the battery is increased role in promoting.Reaction conditions of the humidifying gas from the top of the battery discharge through the fashionable performance of the battery improved effect.In the battery is not humidified,the reaction gas from the bottom of the battery through the battery have a fashionable humidification effect,while the battery discharge performance is also improved to some extent.Fuel cell performance under moist conditions as better than non-humidified conditions.4.Through experimental study found that the battery cover battery liquid flow channel flow reaction gas diffusion layer can cause the battery performance will decrease quickly.At the same time a certain amount of reaction gas flow rate of liquid drainage is advantageous,but also to promote the improvement of fuel cell performance.At the same time is also found that when the battery temperature is 60?,the cathode side air flow 600ml/min,hydrogen flow to the anode side of the battery drainage effect 800ml/min best to achieve the best performance of the battery.