3-D Numerical Simulation of Gas-Liquid Flow in a Minichannel With a Non-Uniform GDL Surface

Abstract

Gas-liquid two-phase flow in rectangular minichannels of polymer-electrolyte membrane fuel cells (PEMFCs) has a major impact on the fuel cell performance and durability. Different from traditional two-phase flow in other applications, water in the PEMFCs is introduced into the minichannel from the gas diffusion layers (GDLs) through random pores of different sizes. Meanwhile, the four channel surfaces may have different wettabilities due to the different materials used. Thus, the microstructure of GDLs and the surface wettability should be considered in investigating the two-phase flow in PEMFC channels. One challenge in simulating PEMFCs is that, full consideration of detailed microstructure of GDL needs extremely large computational time. In this work, we simplified the microstructure of GDL to a number of representative pores on the 2D GDL surface. A 3-D minichannel with 1.0 mm × 1.0 mm square cross section and 100 mm long was used in the simulation. Operating conditions and material properties were selected according to realistic fuel cell operating conditions. Volume of fluid (VOF) method was employed to explicitly track the droplet surfaces emerging from the non-uniform GDLs. Simulation results show that, as the flow develops along the channel, the flow pattern evolves from corner flow on the bottom and side wall to corner flow on the top wall, annular flow and slug flow. The effects of liquid injection rates were studied, and it is found that the high liquid flow rate would accelerate the flow pattern development. The effect of wall surface material wettability was also studied by changing the hydrophobicity of GDL surface and side walls, separately. Simulation results show that the material wettability has a strong impact on the two-phase flow pattern, with a more hydrophilic side walls and/or a more hydrophobic GDL surface being more beneficial for expelling water out of the channel.