Thermal management of fuel-cell stacks using air flow in open-cell metal foam

A new numerical and experimental work investigating the cooling potential of open-cell aluminum foam (using airflow) for fuel cell stacks is described. A model for metal-foam cooling design based on a commercial 500-W proton exchange membrane fuel cell (PEM) stack was simulated and tested experimentally. The new design of the current investigation replaces the existing liquid-cooling channels with compressed aluminum foam having a porosity of 60%. The study considered symmetric and asymmetric heated foam channels subjected to constant heat flux of 1.56 W/cm2, and cooled by airflow at hydraulic-diameter Reynolds numbers in the range 87–657. In the simulations, the thermal energy equations were solved invoking the local thermal non-equilibrium model, which is a more realistic treatment for airflow in metal foam. Local temperatures in the stack, local and length-averaged Nusselt numbers, and friction factors were determined numerically and experimentally. Good agreement between the simulation and experiment was obtained for the local temperatures. The local Nusselt number slightly decreased with distance along the cooling channel, and the length-averaged Nusselt number increased with Reynolds number. As for the friction factors predicted by simulation and obtained experimentally, there was an average difference of about 18.3%. This difference has been attributed to the poor correlation used by the CFD package for pressure drop in metal foam. The new cooling system could remove the 500 W of waste heat of the stack, and would keep the stack within the safe range of operating temperature: 60–90̊ °C.