Abstract
A three-dimensional two-phase lattice Boltzmann model (LBM) is implemented and validated for qualitative study of the fundamental phenomena of liquid water transport in the porous layer of a proton exchange membrane fuel cell (PEMFC). In the present study, the three-dimensional microstructures of a porous layer are numerically reconstructed by a random generation method. The LBM simulations focus on the effects of the porous layer porosity and boundary liquid saturation on liquid water transport in porous materials. Numerical results confirm that liquid water transport is strongly affected by the microstructures in a porous layer, and the transport process prefers the large pores as its main pathway. The preferential transport phenomenon is more profound with a decreased porous layer porosity and/or boundary liquid saturation. In the transport process, the breakup of a liquid water stream can occur under certain conditions, leading to the formation of liquid droplets inside the porous layer. This phenomenon is related to the connecting bridge or neck resistance dictated by the surface tension, and happens more frequently with a smaller porous layer porosity. Results indicate that an optimized design of porous layer porosity and the combination of various pore sizes may improve both the liquid water removal and gaseous reactant transport in the porous layer of a PEMFC.
Highlights
The proton exchange membrane fuel cell (PEMFC) is considered one of the most promising energy conversion devices for future transportation applications, due to its high energy efficiency, high power density, and environment-friendly operations
During PEMFC operations, water is produced by the electrochemical reactions in the cathode catalyst layer (CCL)
Numerical studies of liquid water transport in the porous layer of a PEMFC are conducted focusing mainly on the effects of the porous layer porosity and boundary liquid saturation on the transport behaviors
Summary
The proton exchange membrane fuel cell (PEMFC) is considered one of the most promising energy conversion devices for future transportation applications, due to its high energy efficiency, high power density, and environment-friendly operations. Many experimental and numerical studies have been conducted to investigate the complex transport phenomena in the porous media of PEMFCs [3–14]. These studies, focused mainly on the macro-scale transport processes. Mukherjee et al [31] conducted LBM simulation to examine the two-phase transport process and liquid water flooding phenomena in the porous media of a PEMFC. Effects of several important parameters, including the gas flow velocity, surface contact angle, and gas channel shape, on the liquid water transport characteristics were investigated These early studies prove that LBM simulations are suitable for numerical study of the micro-scale two-phase transport in the complex porous media of a PEMFC.
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