A non-isothermal PEM fuel cell model including two water transport mechanisms in the membrane

A dynamic two-phase flow model for proton exchange membrane (PEM) fuel cells is presented. The two dimensional model includes the two-phase flow of water (gaseous and liquid) in the gas diffusion layers (GDLs) and in the catalyst layers (CLs), as well as the transport of the species in the gas phase. The membrane model describes water transport in a perfluorinated sulfonated acid ionomer (PFSA) based membrane. Two transport modes of water in the membrane are considered, and appropriate coupling conditions to the porous catalyst layers are formulated. Water transport through the membrane in the vapor equilibrated transport mode describes a Grotthus-Mechanism. This is included as a macroscopic diffusion process. The driving force for water in the liquid equilibrated mode is due to a gradient in the hydraulic water pressure. Moreover, electroosmotic drag of water is accounted for. The discretisation of the resulting flow equations is done by a mixed finite element approach. Based on this the transport equations for the species in each phase are discretised by a finite volume scheme. The coupled mixed finite element/finite volume approach gives the spatially resolved water and gas saturation and the species concentrations. In order to describe the charge transport in the fuel cell the Poisson equations for the electrons and protons are solved by using Galerkin finite element schemes. The electrochemical reactions in the catalyst layers is modeled with a simple Tafel approach via source/sink terms in the Poisson eqations, and of the mass balance equations. The heat transport is modelled in the GDLs, and in the CLs. Heat transport through the GDLs in the solid phase, the gas phase and the liquid water phase is included. Heat transport through the membrane is described in two phases, that is, in the solid phase and in the liquid phase. Two heat transport mechanisms are accounted for, heat conduction and heat convection