No abstract

A three-dimensional, multi-species, multi-phase 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 favour 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.

It is the objective of this study to present the 3-dimensional comprehensive computational fuel cell dynamics (CFCD) model of a scaled-down single PEM cell featuring a nominal active surface of 0.0004 m2 for both conventional and serpentine flow field designs. The performance of these two designs are then analysed and compared keeping both anode and cathode inlet gases fully humidified. Then the parallel flow field was modelled under different inlet gas relative humidities (RHa/RHc) representing saturated, moderate, and dry conditions to observe the gain in cell performance. The higher pressure drop of the serpentine flow-field was demonstrated and the magnitude of which might seem to be negligible in the range of 100 Pascal. The simulation results show that a parallel flow-field design with appropriate humidity level can compete with the serpentine counterpart and gives considerably lower pressure drop across the cell. With a grid-independency analysis, it is suggested for the computational power available, the percentage error of important variables (species concentration and averaged current density) between the reference and finer mesh is negligible (< 3%) and the solution time is considerably less.

Abstract. Typical PEM fuel cell models usually involve more than 10 6 mesh elements making the computation very intense. This necessitates an effective way to mesh the computational domain with a minimum number of mesh points while, at the same time, maintaining good accuracy. The meshing strategy in each flow direction is investigated systematically in the current study and it has been found that mesh resolution in different directions has a different degree of influence on the accuracy of solutions. The proposed meshing strategy is capable of greatly reducing the number of mesh elements, hence computation time, while preserving the characteristics of important flow-field variables.