Numerically investigating two-phase reactive transport in multiple gas channels of proton exchange membrane fuel cells

Abstract

Understanding the coupled mechanisms between two-phase flow and reactive transport in proton exchange membrane fuel cells is important for improving cell performance. In this study, a one-dimensional + three-dimensional model is developed to simulate the air–water two-phase flow, mass transport and electrochemical reaction in the cathode side of proton exchange membrane fuel cells. Dynamic water behaviors affected by several forces in three channels are well captured by the volume of fluid method. Effects of liquid water behaviors on pressure drop, mass flow rate, oxygen concentration distribution, current density and especially the distribution characteristics among different channels are discussed. It is found that the current density increases under certain flow patterns such as droplet detachment and water film on the top wall. Compared with single-phase flow, the two-phase flow magnifies the flow maldistribution in different channels, and such maldistribution in turn leads to different water detachment sequence in the three channels. The change of the mass flow rate in the second channel is more sensitive to that in the third channel. Effects of the gas channel wall wettability and channel structures are also investigated. The results show that changing the gas channel as hydrophobic will lead to higher pressure drop, lower current density and poorer flow distribution among different channels, which thus is not desirable in application. Modified structures of rectangle channel and tapered channel are finally explored. Compared with the base case, the tapered channel results in increased flow uniformity and averaged current density by 65.9% and 1.5%, respectively.