Improving the gas flow distribution in a PEMFC stack by removing liquid water from the manifold

This paper studied the oxygen flow distribution in a PEM fuel cell stack numerically. At first, the flow in the stack was simulated as a single phase, and the effect of gradual reduction of manifold height (tapered manifold) on improving the flow distribution between fuel cells was investigated. Standard deviation and non-uniformity coefficient have been used to measure the flow maldistribution. Gradual reduction of manifold height up to 70% in the tapered manifold improved standard deviation and non-uniformity coefficient by 6.9% and 8.4%, respectively. The results of the two-phase simulation showed that the condensation of water vapor in the saturated oxygen could cause the accumulation of liquid water at the end of the manifold. As the smaller droplets merged, the droplet radius formed at the end of the manifold increased until it detached from the manifold wall and entered the last cells. Less liquid water entered the last cell at shorter intervals in the tapered manifold. It was suggested that by creating a water chamber at the end of the manifold, condensed water be collected from the manifold and discharged from the stack. Increasing the mass flow at the manifold inlet and discharging the excess gas through the water collection chamber can push the liquid water into the chamber without causing significant changes in pressure drop.