An integrated modeling approach for temperature driven water transport in a polymer electrolyte fuel cell stack after shutdown

The concept of using controlled temperature gradients to non-parasitically remove excess water from porous media during PEFC stack shutdown has been numerically investigated. An integrated modeling approach focusing both at stack and single cell level is presented. The stack thermal model is developed to obtain detailed temperature distribution across the PEFC stack. The two-phase unit fuel cell model is developed to investigate the detailed water and thermal transport in the PEFC components after shutdown, which for the first time includes thermo-osmotic flow in the membrane. The model accounts for capillary and phase-change induced flow in the porous media, and thermo-osmotic and diffusive flow in the polymer membrane. The single cell model is used to estimate the local water distribution with land or channel boundary condition, and the experimentally validated stack thermal model provided the transient temperature boundary conditions. Two different stack designs are compared to quantify the residual water in the stack. Model results indicate that a favorable temperature gradient can be formed in the stack to enhance the water drainage rate, esp. at anode end cell locations, where freeze/thaw damage has been observed to occur.