Full-scale modelling and thermal analysis of an air-cooled proton exchange membrane fuel cell stack with U-shape gas architecture and close cathode mode

Air-cooled proton exchange membrane fuel cells (ACFCs) typically employ an open-cathode structure but suffer from heat accumulation and low oxidant partial pressure, limiting performance and durability. To address these challenges, a full-scale U-shaped intake ACFC stack model with close cathode was developed, incorporating electrochemical reactions, multicomponent mass transport, Darcy flow, and fluid-solid heat transfer. The model was used to evaluate thermal and output characteristics under varying coolant flow rates. Results indicate that thermal non-uniformity is most pronounced at the end of the flow path. Increasing coolant velocity enhances forced convection and reduces reactant-driven thermal gradients; however, this effect diminishes at higher velocities. A coolant velocity of 5 m/s was found to achieve optimal thermal management and stack performance with minimal auxiliary power consumption. Specifically, increasing coolant velocity from 3 m/s to 5 m/s reduced the stack temperature difference from 17.12 °C to 10.92 °C, while a further increase to 7 m/s only reduced it to 8.32 °C. In-plane temperature uniformity is primarily controlled by coolant flow, with minor influence from reactant distribution, whereas axial thermal gradients are largely independent of reactant flow. Thermal uniformity progressively declines along the flow direction, with upstream cells showing better heat dissipation due to proximity to reactant inlets/outlets. This contributes to localized thermal homogenization and reduced hot spots. These findings provide insights into improving ACFC thermal design for enhanced stability and efficiency.