Lattice Boltzmann Simulations of $CO2$ Bubble Dynamics at the Anode of a $μDMFC$

This paper presents the bubble transport phenomenon at the anode of a micro-direct methanol fuel cell $(μDMFC)$ from a mesoscopic viewpoint. Carbon dioxide bubbles generated at the anode may block part of the catalyst/diffusion layer and also the flow channels that cause the $μDMFC$ malfunction. Lattice-Boltzmann simulations were performed in this paper to simulate the two-phase flow in a microchannel with an orifice which emulates the bubble dynamics in a simplified porous diffusion layer and in the flow channel. A two-dimensional, nine-velocity model was established. The buoyancy force, the liquid-gas surface tension, and the fluid-solid wall interaction force were considered and they were treated as source terms in the momentum equation. Simulation results and parametric studies show that the pore size, the fluid stream flow rate, the bubble surface tension, and the hydrophilic effect between the fluid and the solid wall play the major roles in the bubble dynamics. Larger pore size, higher methanol stream flow rate, and greater hydrophilicity are preferred for bubble removal at the anode diffusion layer and also the flow channels of the $μDMFC$⁠.