The purpose of this work is to use computation fluid dynamics using mesh simulations to model the flow through gas diffusion layers (GDLs), in order to calculate the fundamental properties of the GDL. The study of porosity, tortuosity, liquid and gas permeability, and pore size distribution for GDL’s are the primary focus points in this work. The GDL model geometries seen in this investigation were obtained through three dimensional reconstructed micro-structures from micro X-ray computed tomography (CT). Figure 1 shows the microstructure and streamlines to model the movement of fluid through the GDL. The simulated GDL’s consist of: EP40T, Sigracet 25BA, Sigracet 25BC, GDS3250, and GDS3260.

The tortuosity calculated from simulations is taken at multiple points on the GDL to obtain an averaged value for the sample. The average value is used because the GDL structure is a matrix of random carbon fibers. The liquid and gas phase permeability is important to the calculation of tortuosity because it is a measure of the willingness of a porous media to flow through it. In addition, the simulated results are compared to experimental data through the calculation of the MacMullin number. The MacMullin number is a relationship defined by porosity divided by tortuosity. This number describes the ionic resistance, or resistance to current flow, through the GDL.

References:

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2. Martínez Michael J., Shimpalee, S., Van Zee, J.W., 2009. Measurement of MacMullin Numbers for PEMFC Gas-Diffusion Media. Journal of The Electrochemical Society 156. doi:10.1149/1.3005564
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Figure 1: Model geometry (EP40T) obtained from Micro X-ray CT with streamlines to show the flow.