A Computational Fluid Dynamics Analysis of Heat Transfer in an Air-Cooled Proton Exchange Membrane Fuel Cell with Transient Boundary Conditions

Abstract

In recent studies, it was found that the current density and power density in air-cooled proton exchange membrane fuel cells is limited by heat transfer. The air that serves as both reactant and coolant has a low thermal conductivity which leads to an early onset of membrane overheating at current densities that are typically in the range of 0.3 - 0.4 A/cm^2. In addition, the stoichiometric air flow ratios are in the regime that lead to laminar flow while it is known that turbulent flow leads to higher heat transfer rates and more efficient cooling. It has therefore been suggested to place a turbulence grid before the entrance of such an air-cooled fuel cell, and first experiments have shown that both the current density and power density can be increased while keeping the fan power constant.In order to further improve the heat transfer, it has been suggested to induce pulsating flow to the air stream by sinusoidally varying the fan power as function of time. In this numerical study, a turbulence grid was placed before the entrance of a single air-cooled fuel cell channel with varying distances, and the velocity inlet of the air was varied periodically as function of time. One finding is that the choice of the numerical turbulence model is crucial in this analysis. Results indicate that the best distance between the grid and the cathode inlet is the closest at 2.5 mm which is in good agreement with prior experiments. The transient effects are small but show an additional cooling effect. Figure 1