Predictions of flow regimes in proton exchange membrane fuel cells: An analytical approach

Water management in proton exchange membrane (PEM) fuel cells still remains a topic of much investigation in order to maintain satisfactory cell performance. One specific water management issue relates to the gas-liquid flows that occur when water enters the reactant flow field channels, which are typically microchannels or minichannels. The emergence of liquid water to the flow channel is very unique, starting with a form of liquid droplet. The liquid droplet grows and becomes unstable at high gas velocities. Detachment of unstable droplets leads to various flow regimes possibly observed in active fuel cells, including droplet, slug, film, and pseudo-single-phase flows. In this work, a force balance analysis was conducted to determine stability of a liquid droplet under different operating conditions of great relevance to fuel cell operation. After droplet detachment, a theoretical approach was developed to define which flow regime will form. The force balance analysis considered different wetting scenarios in the channels, and a range of superficial velocities of importance to PEM fuel cells was taken into account.