(690d) Lattice-Boltzmann Simulations of Multiphase Flows in Gas-Diffusion-Layer (GDL) of a PEM Fuel Cell

Effective water management is essential for improved power density and freeze-thaw durability in automotive applications of Proton Exchange Membrane Fuel Cells (PEMFCs). This involves efficient removal of excess water from the cathode catalyst by capillary action through a hydrophobic porous gas-diffusion-layer (GDL). Understanding of the two-phase transport of liquid water and gaseous reactants within these porous materials is limited, due primarily to the challenges of in-situ diagnostics for such thin, optically opaque materials. Transport is typically analyzed by fitting Darcy's Law type expressions for permeability, in conjunction with capillary pressure relations based on formulations derived for media such as soils. Therefore, there is significant interest in developing predictive models for transport in GDLs and related porous media. Such models could be applied to analyze and optimize systems based on the interactions between cell design, materials, and operating conditions, and could also be applied to evaluating material design concepts. Recently, the Lattice Boltzmann Method (LBM) has emerged as an effective tool in modeling multiphase flows in general [1,2], and flows through porous media in particular [3,4]. This method is based on the solution of a discrete form of the well-known Boltzmann Transport Equation (BTE) for molecular distribution, tailored to recover the continuum Navier-Stokes flow [5,6]. The kinetic theory basis of the method allows simple implementation of molecular forces responsible for liquid-gas phase separation and capillary effects. The solution advances by a streaming and collision type algorithm that makes it suitable to implement for domains with complex boundaries. We have developed both single and multiphase LB models and applied them to simulate flow through porous GDL materials. We will present an overview of the methods as implemented, verification studies for both microstructure reconstruction and transport simulations, and application to single- and two-phase transport in GDL structures. The application studies are designed to both improve understanding of transport within a given structure, and to investigate possible routes for improving material properties through microstructure design.

References:

1. Mukherjee, S. and Abraham, J. ?Investigations of Drop Impact on Dry Walls with a Lattice-Boltzmann Model?. Journal of Colloid and Interface Science. 312, 341-354 (2007).

2. Mukherjee, S. and Abraham, J. ?Liquid Crown behavior in Drop Impact on Wet Walls?. Physics of Fluids. 19, 052103 (2007).

3. Schulz, V. P., Becker, J., Wiegmann, A., Mukherjee, P., P. and Wang, C., Y., ?Modeling of Two-phase Behavior in the Gas Diffusion Medium of PEFCs via Full Morphology Approach?. Journal of Electrochemical Society. 154, B419-B426 (2007).

4. Niu, X., D., Munekata, T., Hyodo, S., A., Suga, K., ?An Investigation of Water-gas Transport Processes in the Gas-Diffusion-Layer of a PEM Fuel Cell by a Multiphase Multiple-Relaxation-Time Lattice Boltzmann Model?. Journal of Power Sources. 172, 542-552 (2007).

5. Mukherjee, S. and Abraham, J. ?Lattice Boltzmann Simulations of Two-phase Flow with High Density Ratio in Axially Symmetric Geometry?. Physical Review E. 75, 026701 (2007).

6. Mukherjee, S. and Abraham, J. ?A Pressure-evolution-based Multi-relaxation-time High-density-ratio Two-phase Lattice-Boltzmann Model?. Computers and Fluids. 36, 1149-1158 (2007).