Fundamental Understanding of Water Movement in Gas Diffusion Layer Under Different Arrangements Using Combination of Direct Modeling and Experimental Visualization

Abstract

The purpose of this work is to use direct modeling based Lattice Boltzmann Method (LBM) [1-3] with combination of flow visualization to fundamentally understand the transport of liquid water and air inside the gas diffusion layers (GDLs) used in polymer electrolyte membrane fuel cells (PEMFC). Studies of the water evolution, water saturation, and breakthrough pressure inside GDL under different arrangements are the primary focus in this work. The model geometries of GDLs provided in this study were obtained by three dimensional reconstructed micro-structure from micro X-ray computed tomography (CT) as shown in Figure 1. The experimental setup was similar to that in Ref. 3 with the addition of multiple water injection points and also the compression pressure that can represent the effect of land area of the PEMFC flow-field. The overall predictions of water profile evolution within the GDL agree with the data visualized from the X-ray CT experiment for all cases studied. They also reveal that the water saturation profiles inside the GDL samples and breakthrough pressure are different when the location of water injection point is changed. In addition, the non-compressed GDL provides significantly different mechanism of water transport compared to compressed GDL. Figure 2 shows example of the predictions and experimental data of water evolution inside the SGL10BA GDL with and without compression. The results clearly show that without compression, water spreads to the side of the GDL before it moves up to the top of the GDL. For the compressed GDL, the water transports directly to the top of GDL, where breakthrough pressure is reached. This work will also be extended to include the effect of non-uniform wettability of GDL on water transport and saturation.