Advanced design of a central manifolding device mitigating massive flow resistance in a polymer electrolyte fuel cell stack

Abstract

In a typical reactant supplying system of fuel cells, flow patterns can be classified as U-or Z-shape by the overall flow paths from the inlet to outlet manifolds. For a high power application of fuel cells, simple U- or Z-shape manifold design with single inlet and outlet may cause flow starvation near the reactant feed-stream inlet and flow mal-distribution along the manifold flow path which have negative effects on both life-time and system performance. In this study, two types of central manifold designs are presented to overcome the flow imbalance and to minimize the manifold size for a large-scale fuel cell system. For effective and reliable prediction on the thermo-flow characteristics of the reactant flow over the entire fuel cell stack domain, a numerical model was developed using a simplified flow resistance model with an empirical porous concept. A number of case studies were performed to figure out the strong time-dependent flow behaviour and the flow distribution along the manifold. The heat generation effect inside fuel cells on the primary manifold flow patterns was also investigated by applying a volume averaging heat transfer model to the multi-cells fuel cell stack, which enables us to estimate the effect of the temperature-dependent physical properties on the mass flow uniformity. The results showed that the stable and load-independent flow uniformity is very design specific, which is closely associated with the design of central manifolding devices in order to achieve the enhanced volumetric power density and the reliable long-lasting operation of fuel cells.