One-dimensional comparison of numerical approaches on two-phase flow in the membrane electrode assembly of PEMFC

Numerical simulation of two-phase flow is important for the performance evaluation of proton exchange membrane fuel cell (PEMFC). Exchange of water between vapor and liquid phases in the gas diffusion layer (GDL) was considered by Nguyen and co-workers (2000) using the evaporation and condensation rate constants. Hsuen and Yin (2011), in which a pseudo-phase-equilibrium function approximates the vapor/liquid phase equilibrium, proposed another two-phase flow approach. Both methods are capable of predicting the cell performance and the species concentration profiles in the membrane electrode assembly (MEA) without the need to track liquid water front in the GDL explicitly. The present study compares the numerical results of these two approaches in detail. In addition, one-dimensional simplified semi analytical solution based on the instantaneous phase equilibrium assumption is used to validate the numerical calculations. The evaporation/condensation approach allows the existence of super-saturated vapor near the interface of cathode GDL and membrane. Thus, membrane can be better hydrated near the interface once liquid water emerges in the GDL as compared to the pseudo-phase equilibrium method. Consequently, smaller ohmic resistance and hence better cell performance are observed with Nguyen's prediction once liquid water appears in the GDL. (c) 2016 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.