Heat transfer in polymer electrolyte fuel cells

Abstract

A three dimensional computational fluid dynamics (CFD) model of a polymer electrolyte membrane fuel cell (PEMFC) stack has been developed in order to study heat transfer in single-cell and two-cell stacks. In order to simplify the computational model, the electrochemical and water transport aspects of fuel cell operation were decoupled from those of heat transfer; the PEMFC fuel cell membrane electrode assembly (MEA), which comprises the electrode and electrolyte functional layers, was substituted with an electrically heated-plate to simulate the heat generated by an MEA. A fuel cell stack was manufactured and instrumented with calibrated thermocouples to measure the temperature distribution. The effect of reactant gas flow rate and cell thermal power density on the temperature distribution within the stack was studied with a view to validating the CFD model over a broad range of operating conditions. Also, in order to study the effects of natural and forced convection on the temperature distribution in the stack, an infra-red imaging camera was used. The predicted temperature distribution showed good agreement with the experiment over a wide range of gas flow rates, both in terms of local temperature distribution and overall energy balance. Results show that increasing the number of cells in a stack from one to two causes in a larger temperature variation, and therefore heat management in the stack becomes increasingly critical. The validated computational model was used as a modelling framework to design and test different cooling plates for stacks in order to overcome this issue. As a result, the bipolar plate in the two-cell stack was replaced with an air-cooled cooling plate in order to minimise temperature variation and to improve overall stack performance.