Proton exchange membrane fuel cell modeling with diffusion layer-based and sands-based capillary pressure correlations : Comparative study

Although the Leverett-Udell correlation has been proven inaccurately to describe the capillary pressure-saturation (p_c-s) characteristics of a gas diffusion layer (GDL), this correlation is still extensively applied in the modeling of proton exchange membrane (PEM) fuel cells. The question of how much error is introduced into the determination of the cell current-voltage performance by using Leverett-Udell correlation has not been answered satisfactorily. This study numerically evaluates cell performance using a three-dimensional, two-phase, and non-isothermal fuel cell model, which incorporates the Leverett-Udell correlation and the experimentally measured p_c-s correlation. The performances predicted by the two models were compared for various model parameters - GDL porosity (0.6 and 0.9), GDL tortuosity (1.5 and 2.5), and coefficient of water vapor condensation rate (500s^-1 and 5000s^-1). Numerical results indicate that introducing the cosine of the contact angle into the Leverett-Udell correlation inaccurately represents the effect of wettability on the capillary pressure. The Leverett-Udell correlation with a contact angle far larger than the actual contact angle can nevertheless yield a cell performance that is close to that obtained from the experimentally measured p_c-s correlation. Quantitative modeling using the Leverett-Udell correlation is not recommended. However, qualitatively, the comprehensive PEM fuel cell model with the Leverett-Udell correlation can be used for preliminary screening in cell design and performance estimation. © 2014 Taiwan Institute of Chemical Engineers.