A CFD INVESTIGATION OF EFFECTS OF FLOW-FIELD GEOMETRY ON TRANSIENT PERFORMANCE OF AN AUTOMOTIVE POLYMER ELECTROLYTE MEMBRANE FUEL CELL

摘要

A three-dimensional, multispecies, multiphase polymer electrolyte (PEM) fuel cell model was developed in order to investigate the effect of the flow-field geometry on the steady-state and transient performances of the cell under an automotive operation. The two most commonly used designs, parallel and single-serpentine flow fields, were selected as they offer distinctive species transport modes of diffusion-dominant and convection-dominant flows in the porous layers, respectively. It was found that this difference in flow mode significantly effects membrane hydration, the key parameter in determining a successful operation. In a steady run, a serpentine flow field increased the averaged current density under the wet condition due to superior water removal, but this had a negative effect on the cell in the way that it caused membrane dry-out if dry reactant gases were used. The transient operation, on the other hand, seemed to favor the combination of a serpentine flow field and dry reactant gases, as it helped in the removal of product water and speeded up the transport of reacting species to the reactive site to find equilibrium at the new state with minimum time delay and current overshoot or undershoot, which is the most important aspect of a dynamic system.