| Popis: |
In polymer electrolyte fuel cells (PEFCs), a gas diffusion layer (GDL) is a critical component to prevent flooding and to improve the cell efficiency under high current density operation. To advance the experimental method for evaluation of liquid water transport in GDL, this study proposes a method, termed scale model experiments. In this method, enlarged GDL structures are reproduced by a 3D printer, and simulated water behavior is observed with similarity conditions satisfying the flow in the GDL. The lattice Boltzmann simulation is applied to the enlarged model experiments and identifies dominant forces in the water dynamics. First, simulations are conducted to compare flow patterns at two different scales of GDL, the actual scale and 313 times enlarged structures, with combinations of two immiscible fluids. The results suggest that fluid behavior can be considered similar at the different scales, when the Capillary number is low enough for the flow to be dominated by capillary forces, at Ca = 3.0×10-3, with the additional condition of negligible buoyancy. Next, experiments with two types of 313 times enlarged GDL structures are conducted with silicone oil and water of similar densities, and the flows are compared to the simulation results. These suggest that the water transport in the GDL can be successfully reproduced by the enlarged model experiments. As similarity conditions, the Weber number must be kept below the order of 10-1 to suppress inertial forces as well as the Capillary number must be below the order of 10-3 for smaller viscous forces. Careful attention must be paid to the viscous forces of the two fluids in a relatively-uniform structure GDL. Finally, an experiment of water transport in the GDL with a channel is demonstrated, showing the effectiveness of the proposed experimental approach for designing GDL structures tolerant to flooding. |
