Predicting Water-Droplet Detachment from GDL/Channel Interfaces in PEM Fuel Cells

Abstract

An analytical model is presented for predicting the critical air-flow velocity at the onset of water-droplet detachment from the GDL/channel interfaces in PEM fuel cells. Our model is based on the force balance between pressure drag that tends to detach the droplet and surface tension that tends to hold the droplet in place. In the present work, we consider the flow regime in which pressure drag, which arises from inertia effects, dominates over viscous shear - this is the flow regime of interest in real-world PEM fuel cell applications, both automotive and stationary. Our analytical model predicts that the critical air-flow velocity varies inversely (to the 2/3 power) with water-droplet size. It further predicts that making the GDL surface more hydrophobic, decreasing contact-angle hysteresis, and shrinking channel height reduce the critical air-flow velocity. Model predictions are compared with experimental data available from the literature and reasonably good agreements are obtained.