Numerical investigation on the effect of water vapor phase change on the distribution of the oxygen flow in a PEMFC stack

In a PEMFC, the proton conductivity of the membrane depends on its water content and using saturated reactants can improve the performance of the fuel cell. The heat transfer between saturated reactants and the walls causes condensation of part of the water vapor in the inlet gas. Phase change affects the distribution of gas flow among the cells in the stack. In this paper, CFD is used to study the effect of water vapor phase change on the distribution of oxygen flow in the cathode side of a polymer electrolyte membrane fuel cell stack with 26 cells. For this purpose, a code is developed in OpenFOAM software and validated with experimental data for the single-phase flow distribution. Three different boundary conditions are applied to the walls of the manifold: constant temperature, free and forced heat convection. The results indicate that water generated from condensation on the lower wall of the inlet manifold enters the first cell. Also, the accumulation of water in this area reduces the flow velocity at the entrance of the first cell. The condensed water vapor on the upper wall of the inlet manifold moves to the end of the stack. Part of the water enters into the four last cells, and the other part returns to the manifold due to the vortex. Therefore, the first cell and the last four cells receive less reactant than other cells. The non-uniform flow distribution parameter increases by up to 1425% on using saturated oxygen and under forced convection conditions.