Effect of fiber curvature on gas diffusion layer two-phase dynamics of a proton exchange membrane fuel cell

TL;DR

This study investigates how fiber curvature in gas diffusion layers affects two-phase flow dynamics in proton exchange membrane fuel cells, revealing that fiber shape influences water transport, saturation, and droplet behavior, which can inform better GDL design.

Contribution

It introduces a stochastic reconstruction method for GDLs with varying fiber curvatures and analyzes their impact on two-phase flow dynamics through pore network modeling and simulations.

Findings

Increased fiber curvature enhances pore connectivity and water saturation.

Straight-fiber GDLs show closer resemblance to physical GDLs but with higher uncertainty.

Water saturation and droplet behavior vary significantly with fiber curvature.

Abstract

The dynamics of two-phase flow within the cathode of a proton exchange membrane fuel cell, particularly in Gas Diffusion Layers (GDLs) with varying fiber curvatures, remain underexplored. Using a periodic surface model, we stochastically reconstruct three GDL types with different fiber curvatures, incorporating vital parameters derived from a physical GDL. Considering the randomness in reconstruction, the structure generation process is iterated four times for each GDL type, enabling an ensemble average analysis. Pore network models are adopted to reveal disparities in these GDL porous structures. The subsequent two-phase simulations are conducted to explore liquid transport through these GDLs and interfaces to assembled gas channels. Time-varying GDL total, local water saturation, and capillary pressure are investigated. Results show stochastic reconstructions exhibit similar frequency peak ranges in pore and throat diameters, and coordination numbers, but diverge from the physical GDL. Bigger fiber curvature tends to enhance pore network connectivity by increasing smaller pores, leading to heightened water saturation and capillary pressure. Straight-fiber GDLs, compared to curved-fiber GDLs, show greater potential proximity to the physical GDL in terms of overall water saturation and capillary pressure but are also accompanied by increased uncertainty. Despite similar layer porosity, water saturation in the same layer of all samples differs increasingly from the inlet to the outlet. Water breakthrough and detachment near the GDL can induce significant water saturation instability at the GDL and gas channel interface. Detached droplets in gas channels connected with straight-fiber GDLs exhibit larger sizes and slower movement than those in channels assembled with curved-fiber GDLs. These findings can be utilized in future GDL design and optimization.