燃料电池气体扩散层的分形模型研究

Study on Fractal Model of Fuel Cell Gas Diffusion Layer

气体扩散层(GDL)是燃料电池的重要组成部分,一般是以碳纸为材料的一种多孔介质,其内部结构在一定尺度范围内表现出分形特征。本工作基于分形理论、菲克定律、气体扩散层表面特性和气液两相流动规律建立了关于气体扩散系数的分形模型。研究结果表明:有效扩散系数与面积分形维数、孔隙率成正比,与迂曲度分形维数、液相饱和度成反比。通过比较模型预测的气体有效扩散系数与已有实验数据发现,气体扩散层的表面特性即亲水性和疏水性对扩散系数的影响较大,在较低液相饱和度情况下,经过疏水处理的扩散层的气体扩散性能明显优于亲水扩散层。新建立的气体扩散系数模型可准确描述气体扩散层中的扩散规律,对气体扩散层的设计具有一定的指导意义。

G as diffusion layer(GDL)is an important part of fuel cell.It is a porous medium made of carbon paper.Its internal structure shows fractal characteristics in a certain scale.Based on the fractal theory,Fick's law,the surface characteristics of gas diffusion layer and the law of gas-liquid two-phase flow,a mathematical model of gas diffusion coefficient was established.The results show that the effective diffusion coefficient is directly proportional to area fractal dimension and porosity,and inversely proportional to tortuosity fractal dimension and liquid saturation.By comparing the effective diffusion coefficient predicted by the mathematical model with the existing experimental data,it is found that the surface characteristics of the gas diffusion layer,i.e.hydrophilicity and hydrophobicity,have a great influence on the diffusion coefficient.In the case of low liquid saturation,the gas diffusion performance of the hydrophobic-treated diffusion layer is obviously better than that of the hydrophilic diffusion layer.The new mathematical model of gas diffusion coefficient can accurately describe the diffusion law in the gas diffusion layer,which has a certain guiding significance for the design of gas diffusion layer.