Development of two-phase flow regime specific pressure drop models for proton exchange membrane fuel cells

Abstract

Water is an inevitable byproduct in proton exchange membrane fuel cells that can lead to complex two-phase flow throughout the cell's components, including the flow field channels utilized for gas delivery. A modified Lockhart–Martinelli (LM) approach based on unique water introduction through the gas diffusion layer is used here to predict the gas–liquid pressure drop in these channels by modifying the Chisholm parameter C. This paper exclusively uses experimental data of two-phase flow multipliers from four sources in the literature, all of which are obtained from active fuel cell operation. C does not appear to change strongly as a function of temperature, relative humidity, or air stoichiometry, but does vary significantly with the current density. This is especially true at low current densities (<500 mA cm−2). To capture this behavior, C is defined as a flow regime dependent parameter based on a flow regime map from the active fuel cell data. In addition to the traditionally used slug, film, and single-phase regimes, an ‘accumulating’ flow regime is proposed to capture the behavior of C and two-phase flow multipliers at low current densities. The proposed accumulating flow regime is consistent with visual observation reported in the literature. In addition, the developed LM approach can be employed to optimize fuel cell flow field design and operation.