| A comprehensive, multi-component, multi-phase numerical model is developed to study methanol crossover, water crossover, transient start-up, and bubbly flow in the anode channel of a direct methanol fuel cell (DMFC). The model is capable of predicting the performance characteristics for passive and semi-passive DMFCs supplied by methanol in liquid or vapor phase. It is found that the most effective method to control methanol crossover is to manage the water crossover through the membrane. A decrease in water crossover results in a significant reduction in methanol crossover. The transient response time of a vapor-feed DMFC fed with pure methanol is reported to be primarily a function of the cell load. Depending on the current density, either mass consumption in the catalyst layers or diffusive liquid transport in the anode is the dominant factor on the transient response time. Finally, significant changes in the gas volume fraction of the bubbly flow in the anode channel of passive and active DMFCs are explained. |
