A comprehensive three-dimensional model coupling channel multi-phase flow and electrochemical reactions in proton exchange membrane fuel cell

Abstract

As a clean electrochemical energy conversion device, proton exchange membrane (PEM) fuel cell will play great effect in the carbon neutral society. It is widely recognized as a challenge to couple the multi-phase flow in gas flow channel and the electrochemical activities in the electrodes in PEM fuel cell modeling. In this study, a two-fluid model is developed to describe the multi-phase flow in the whole cell, in conjunction with the transport phenomena and electrochemical reaction kinetics. We assume the analogy between micro channel and porous media, and derive the gas/liquid velocity ratio for multi-phase flow in channel through Darcy's law for two-phase flow, which is expressed as a function of gas/liquid viscosity ratio and liquid saturation. Integration of the two-fluid model makes it able to predict the two-phase pressure drop and local liquid saturation in gas flow channels in an operating fuel cell. A sub-model of liquid water coverage at the GDL (gas diffusion layer) surface is also developed and incorporated into the model to study the impact of various contact angles at GDL surface on cell performance. The liquid saturation profiles along the flow direction are compared with literature data with reasonable agreement achieved. The model is employed to study a flow field of five parallel channels connected with an inlet/outlet manifold. It shows that multi-phase flow in the gas flow channel leads to more non-uniform flow and oxygen distributions, and hence a larger concentration loss under high current densities than the single-phase channel flow model.

Keywords

• PEM fuel cell
• two-fluid model
• gas/liquid velocity ratio
• surface coverage
• surface contact angle