PEMFC梯度扩散层内两相传输特性的孔隙网络模拟

Pore Network Simulation of Two-phase Transport Characteristics in Gradient Diffusion Layer of PEMFC

为了探究孔隙率的梯度化对气体扩散层内气液两相传输特性的影响,本文采用三维孔隙网络模型计算了不同孔隙率梯度值下扩散层内液相饱和度分布、气液相界面和氧气有效扩散率随液相饱和度的变化曲线,并从孔隙尺度水平对孔隙率梯度的作用机制进行探究。研究结果表明:引入孔隙率梯度能够显著地抑制液相水侵入气体扩散层,有利于气体的传输,且随着梯度化程度的增大,抑制能力增强。同时,随着梯度化的提高微孔层自身的干燥气体扩散率下降。因此,综合上述两者的作用,本文给出了最佳的孔隙率梯度值。

To investigate the effect of graded porosity on gas-liquid two-phase transmission characteristics in gas diffusion layer,three-dimensional pore network models are employed to represent the gas diffusion layers with varied graded porosity value,and the liquid saturation distribution, gas-liquid interface and the oxygen effective diffusivity as a function of liquid saturation are calculated. Additionally,the mechanism of graded porosity is expounded from the viewpoint at the pore level. The results demonstrate that the introduction of graded porosity can obviously inhibit the invasion of liquid water in gas diffusion layer,which is conducive to the transmission of gas.Moreover,with the increase of gradient,the inhibition ability is enhanced.Simultaneously,the diffusivity of the dry gas in the microporous layer decreases with the increase of the gradient.Therefore,the optimal graded porosity value is obtained by considering the above two factors.