Water Management in PEM Fuel Cells : The Effects of Gravity on Vertically Positioned Flow Channels

Abstract

A unique device is used to emulate water droplet emergence from a porous electrode and slug formation in the gas flow channel of a polymer electrolyte membrane fuel cell. Liquid water emerges from a pore forming a droplet, which grows to span the cross-sectional area of the channel and transitions to a slug that then detaches and travels towards the channel exit. Droplet growth, slug formation, detachment, and motion are analyzed using pressure-time traces and MATLAB. Slug volume is controlled primarily by channel geometry, interfacial forces, and the effects of gravity. A physics-based model is presented to predict slug volumes and pressure drops for slug motion. From these results, the amount of power required to remove water from a flow channel is calculated. Results showed that the vertically positioned flow channel studied in this experiment is less power efficient than the previous, and currently, studied horizontal positioned flow channels.