Numerical Simulation And Analysis Of Transmission Parameters For Compressed Gas Diffusion Layer Microstructures

The proton exchange membrane fuel cell(PEMFC)has outstanding advantages such as zero emission,low noise and high power density..In PEMFC,the assembly pressure must be carefully designed.Large assembly pressure helps to avoid gas leakage and reduce the contact resistance of the fuel cell,but it also leads to an increase in the flow resistance due to structure deformation,which brings new problems to the PEMFC hydrothermal management and performance.The gas diffusion layer(GDL)plays a major role in supporting the electrode of PEMFC.It is of great significance to study the structure deformation and transport characteristics in the GDL under the i MPact of assembly pressure.In this study,the microstructure of GDL is established by random reconstruction method,and then the finite element method(FEM)is employed to obtain the GDL structure under the compression force.Finally,the single-phase gas transport model is used to study the transport characteristics along the in-plane and through-plane directions in the GDL..The effect of uniform compression on the relative effective oxygen diffusion coefficient,intrinsic permeability,relative effective thermal conductivity and relative effective conductivity in GDL along the two directions,and the effect of non-uniform compression on the oxygen diffusion in the GDL are studied.The GDL material peoperty on the oxygen diffusion is also studied.It is found that under uniform compression,the through-plane has smaller transport coefficients than the in-plane direction when the same compression ratio is applied.As the compression ratio increases,the effective oxygen diffusion coefficient and the intrinsic permeability of the two transport directions decrease,and the effective thermal conductivity and the effective conductivity increase.The anisotropy of the GDL has great influence on the rate of change of the compression-relative effective oxygen diffusion coefficient curve,and has little effect on the rate of change of the compression-inherent permeability curve.When the compression is relatively small,the assembly pressure has less effect on the relative effective thermal conductivity and electrical conductivity.The empirical formulas between the assembly pressure and the four transport coefficients are proposed for the two transport directions.The effect of non-uniform compression on the oxygen diffusion coefficient is then analyzed.The results are as follows: the oxygen diffusion in the GDL is greatly affected by non-uniform compression.In the in-plane direction,when the compression ratio exceeds 30%,the oxygen diffusion capacity of GDL decreases significantly;in the through-plane direction,the increase of the compression ratio has less influence on the oxygen concentration under the flow channel,but causes the oxygen concentration under the rib to decrease.It is especially obvious when it is far away from the channel.Finally,the influence of material property on the oxygen diffusion in the GDL after compression is studied.As the GDL thickness and fiber diameter decrease and the porosity increases,the oxygen diffusion capability in the compressed GDL increases in the in-plane direction;in the through-plane direction,the oxygen concentration under the flow channel and the rib increases simultaneously.Under the rib the oxygen concentration rises more significantly and the oxygen concentration gradient between the channel and the rib increases.The porosity and thickness of the GDL have great influence on the oxygen diffusion in the compressed GDL,and the fiber diameter has little effect on the oxygen diffusion in the compressed GDL.