Transient numerical fluid analysis on gas distribution to anode cells of a fuel cell stack under start-up condition

Abstract

Catalyst degradation on both the anode and cathode sides is one of the most critical problems caused by lack of hydrogen in each channel in the active area of a polymer electrolyte fuel cell. Especially when a fuel cell stack is in a start-up sequence for an automotive fuel-cell system consisting of hundreds of fuel cells, the initial air filling all the anode flow fields should be exchanged with hydrogen as soon as possible to avoid forming a hydrogen-air front on the cell surface, as this front can create a “local cell” within a single cell causing carbon corrosion and platinum dissolution on the catalyst layer in a membrane electrode assembly. This local cell should thus be prevented from forming in any cells of a fuel cell stack. Just as importantly, to avoid the hydrogen-air front in any cell, hydrogen should be distributed between the cells equally even if this gas distribution process is for a transient manifold. Gas distribution in a gas and coolant manifold has been well reported, but usually for the steady state. In this study, to comprehend the flow condition in the anode flow field, especially in a distribution manifold, we performed transient three dimensional numerical analysis on the anode flow field of a fuel cell stack. Without any simplification such as using an equivalent pressure drop model like porous material, the full geometry was directly calculated for flow simulation in the all channels of 200 cells of a fuel cell stack. It was clarified that (1)the flow pattern in the manifold causes a maldistribution between the cells in a transient state, (2)this maldistribution grows arrogant with the increase of initial Re_in,0 number and (3)the initial maldistribution in the transient process persists during the start-up process and is never fully obliterated.