Modelling of Internal Manifold Flow Distribution in PEMFC 2021-26-0340

In a Polymer Electrolyte Membrane Fuel Cell (PEMFC) uniform reaction rate is very crucial to obtain maximum performance and to maintain the life of the cells. In PEMFC stack manifold plays an important role in maintaining uniform flow distribution of reactants (hydrogen, air and coolant) to the cells. Many studies have been carried out for examining the effect of manifold on flow distribution and pressure drop. Most studies are limited to small scale level (5 to 10 kW stack). This paper describes large scale fuel cell stack manifold design, flow distribution and pressured contours which is suitable for automotive vehicles (30 to 50 kW). The design consists of simplified scaled up fuel cell stack with cells connected in the series. Modelled the effect of internal manifold geometry of the fuel cell stack on pressure and flow distribution to the cells. Hydrogen and air is supplied to the cell using an L-shaped inlet manifold which is integrated in the end-plate of the fuel cell stack assembly. The inlet and outlet manifold flow characteristics are studied by plotting the pressure contours and velocity distribution across the cell entry and exit. The gases entering the end-plate entry has to take two 90⁰ turns to reach the internal manifold. In this design, turbulence and non-uniform gas distribution to the cells was observed. This design was replaced with a straight converging manifold to achieve the uniform flow distribution in the cells. Results confirmed that converging type manifold is very effective for PEMFC stack consisting of more number of cells with serial configuration. The effect of two types of bipolar plate materials (graphite and metallic) was also studied. The graphite bipolar plate has comparatively higher thickness (around 3mm). The thickness of metallic bipolar plate is in the order of 0.6mm with a sheet thickness of 0.1mm due to higher strength and formability. The height of the metallic fuel cell stack is comparatively lesser than the graphite stack, which resulted in more uniform flow distribution of reactants to the cells. Two fuel cell stack made of graphite and metallic bipolar plate consisting of 120 cells were modelled for comparison. Since the metallic stack consumed 50% less space compared to the graphite stack, another metallic fuel cell stack with 180 cells were modelled which can deliver 50% more power compared to the 120 cell stack.