Flow control of under-rib convection enhancing the performance of proton exchange membrane fuel cell

Abstract

Flow-field design is one of the most important issues in the performance of proton exchange membrane fuel cells (PEMFCs). This paper proposes a numerical analysis-based design of the serpentine flow-field patterns equipped with sub-channels and by-passes to control the under-rib convection and thus improve the PEMFC performance. The experimental results show that addition of sub-channels and by-passes between the conventional channels changes the direction of under-rib convection. If reacting gases flow in the same direction as the neighboring main channels, the under-rib convection shows a flow from the main channels to the sub-channels which not only reduces pressure drop but also enhances uniform gas supply and water diffusion. On the other hand, if in the direction opposite to that of the neighboring main channels, the under-rib convection shows a flow from the inlet side towards the outlet side across the sub-channel as in the conventional serpentine channels. Analyses of the local transport phenomena in the cell suggest that the inlet by-pass supplies the reacting gases uniformly from the entrance into the sub-channels and the outlet by-pass enhances water removal. Novel serpentine flow-field pattern employing sub-channels and by-passes shows uniform current density and temperature distribution by uniformly supplying the reacting gas. Furthermore, performance improvement of around 20% is observed from the experimental performance evaluation. As a result, longer battery life is expected by reducing the mechanical stress of membrane electrode assembly (MEA).