5.7 CHAPTER SUMMARY
This chapter discusses the transport phenomena in PEM fuel cell in the absence of liquid water or ice, more specifically, the transport of the gaseous reactants and water vapor. The key points in this chapter are summarized as follows:
• Diffusion and convection are the two major mechanisms for water vapor and gaseous reactant species transport in PEM fuel cells. Convection dominates in gas flow channels (GDCs), whereas diffusion usually dominates in gas diffusion layers (GDLs) and catalyst layers (CLs); both molecular and Knudsen diffusion are important because of the small pore dimension.
• Two approaches, the constant-flow and variable-flow formulations, are presented and discussed for flow modeling. The constant-flow ...