Gas−Liquid Two-Phase Flow in Minichannels with Liquid Side Introduction

Abstract

In the present work, computational fluid dynamics (CFD) modeling with a volume of fluid (VOF) method was used to understand gas-liquid two-phase flow in PEM fuel cell flow channels under typical fuel cell flow conditions. Simulations with different liquid water introduction manners to flow channels were discussed to resemble liquid water transport in flow channels in active fuel cells. Those introduction methods included side liquid introduction through a number of ports, continuous liquid introduction along the channel with uniform and nonuniform flow rates, and liquid water introduction from the inlet together with the gas phase. The simulated results showed that the side introduction of water increases the water accumulation near the end of the channel and the gas slugs are significantly elongated, compared to the cases with water introduction from the inlet. When water was introduced nonuniformly along the channel with more near the outlet of the channel, there appears to be less probability of slug formation in the channel. With low liquid to gas volumetric flow ratios as encountered in fuel cells, the flow pattern changed between slug flow and stratified flow, depending on different liquid introduction manners. When water was introduced into the channel from ports on the bottom wall, it emerged and accumulated near the port region before slugs formed, detached, and purged out of the channel, causing high pressure drop and pressure drop fluctuations. When the wettability, or contact angle, of the channel walls varied, liquid water tended to attach to the wall surface with low contact angles, namely, more hydrophilic surface. In addition, the change in surface contact angle can also lead to the change in flow patterns. The slug frequency decreased with an increase in the port size. With increasing of the port number, more liquid tended to accumulate in the channel.