Heat transfer simulation of a single channel air-cooled Polymer Electrolyte Membrane fuel cell stack with extended cooling surface

摘要

A Polymer Electrolyte Membrane (PEM) fuel cell is an electrical power generator utilizing a hydrogen-based fuel reactant and oxygen in a reversed electrolysis reaction, with byproducts of water and heat. The application is sensitive to temperature; more power is generated at elevated operating temperatures, but excessive cell temperature causes dehydration to the membrane electrolyte and subsequent power decline as well as cell deterioration. The power-to-weight ratio and reduced parasitic load, which are the main advantages of an air-cooled system, pushes the research tendency to replace water cooling with air cooling. This work analyzes the heat transfer characteristics, using analytical and Computational Fluid Dynamics (CFD) tools, of a 3 kW PEM fuel cell stack which is equipped with a single cooling channel on each bipolar plate. The base stack design consisting of 73 bipolar plates refers to an industrial water-cooled PEM fuel cell stack available at the Faculty of Mechanical Engineering, University of Technology MARA. From the results of the coolant flow over the base stack design, extended surfaces (fins) was added at an optimized geometry to enhance the heat transfer. Both designs were subjected to a heat flux magnitude of 1.6 times greater than theoretically required, and showed excellent simulated cooling capability of 100% cooling effectiveness when subjected to flows at Reynolds number of 800 and above. Addition of extended cooling surfaces further improves the thermal gradient reduction within the plate by 30%. Though still requires practical evidence, the simulation analysis has provided the groundwork of air cooling applicability in replacing water cooling for a 3 kW PEM fuel cell stack.