Numerical Investigation On Liquid Water Transport And Effective Transport Coefficents In GDL Of PEMFC

In response to global climate change,many countries have pledged to reduce carbon emissions.One of the key factors is to replace polluting fossil energy with clean energy.Proton exchange membrane fuel cell(PEMFC)with its high energy conversion efficiency,is regarded as one of the important means of hydrogen energy utilization.However,the working temperature of PEMFC is low,and the condensation of water is almost inevitable.The large accumulation of liquid water in the porous electrode will form water flooding,which seriously hinders the diffusion of reaction gas to the reaction site and greatly reduces the performance of the PEMFC.This paper firstly reconstructs the microstructure model of the gas diffusion layer(GDL)based on the "stochastic" method.Based on this pore-scale model,the volume of fluid method is used to study the liquid water transport in GDL.According to the phenomenon of water transport in macro-cracks at the interface of microporous layer and GDL,the effects of two ways of introducing water without crack and with crack on saturation and spatial distribution of liquid water in GDL are investigated.The transport process of water in GDL under different permeable pressures and contact angles shows that hydrophobic treatment increases the permeable pressure required for water to break through GDL.The existence of liquid water will affect the effective transport coefficients of GDL.Based on the spatial distribution of liquid water obtained in water transport simulation,the variation law of effective thermal conductivity and effective gas diffusivity when GDL contains water is studied.Compared with the simulation results of GDL without water,it is found that the existence of liquid water significantly increases the resistance of oxygen diffusion,but the improvement of thermal conductivity is very limited.Finally,with saturation as a variable,the effective thermal conductivity and effective gas diffusivity of GDL are fitted to linear equation and exponential equation(Bruggeman relational form),respectively.Then,the correction formulas of effective thermal conductivity and effective gas diffusivity are applied to the three-dimensional two-phase computational fluid dynamics model of PEMFC,and it is found that the correction of gas effective diffusivity has a great influence on the results of PEMFC simulation,while the effect of saturation on thermal conductivity of GDL and simulation results of PEMFC is negligible.