Abstract
In order to model the liquid water transport in the porous materials used in polymer electrolyte membrane (PEM) fuel cells, the pore network models are often applied. The presented model is a novel approach to further develop these models towards a percolation model that is based on the fiber structure rather than the pore structure. The developed algorithm determines the stable liquid water paths in the gas diffusion layer (GDL) structure and the transitions from the paths to the subsequent paths. The obtained water path network represents the basis for the calculation of the percolation process with low calculation efforts. A good agreement with experimental capillary pressure-saturation curves and synchrotron liquid water visualization data from other literature sources is found. The oxygen diffusivity for the GDL with liquid water saturation at breakthrough reveals that the porosity is not a crucial factor for the limiting current density. An algorithm for condensation is included into the model, which shows that condensing water is redirecting the water path in the GDL, leading to an improved oxygen diffusion by a decreased breakthrough pressure and changed saturation distribution at breakthrough.
Highlights
Water management is very important for the efficiency, stability and durability of polymer electrolyte membrane (PEM) fuel cells
The model follows the assumption that each water filled region in the gas diffusion layer (GDL) is confined by at least two menisci, which are spanning between object pairs, respectively
The experimentally determined properties of the same carbon paper GDL are used as model input parameters (Table 1, Toray TGP-H-060) and as used in the experiments by Flückiger et al For the experimental data, Flückiger et al could extract the local porosity by analyzing the 3D X-ray adsorption data
Summary
Water management is very important for the efficiency, stability and durability of polymer electrolyte membrane (PEM) fuel cells. Pore network models are very helpful for understanding the general dependencies of the liquid water transport phenomena in porous materials for fuel cells [17,18,19,20,21,22,23]. To examine the influence of the GDL structure and local wetting properties, we developed a percolation model using the GDL design parameters as a direct input This includes the distributions of fiber contact angle, fiber size and orientation, as well as spatially varying porosities. It is a novel approach to extend present discrete pore network models towards a more realistic description of the liquid water transport in the void structure of the GDL. We developed and included an algorithm describing the discrete liquid water formation and transport due to phase change for modeling the two-phase water transport when coupling to a whole fuel cell model in future work
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