Based on the requirement of water management for a direct methanol fuel cell, this paper analyzes qualitatively the mechanism of occurrence and development of a two-phase countercurrent flow with corresponding transpo...Based on the requirement of water management for a direct methanol fuel cell, this paper analyzes qualitatively the mechanism of occurrence and development of a two-phase countercurrent flow with corresponding transport phenomenon in the PEM. A one-dimensional, steady state quantitative model of heat and mass transfer in internal volumetric ohmic heating porous media saturated by liquid and vapor phases is developed. The effects of capillarity, electro-osmotic drag and phase change are included. Two im-portant formulas to calculate the theoretical length of two-phase zone δ t and determine the critical criterion |?ω /γ |cr for dryout in PEM are deduced. By use of these two dimen-sionless parameters, dryout of PEM can be easily predicted. Theoretical temperature, pressure and saturation profiles within the two-phase region are obtained numerically, which can help to explore the performance of a DMFC operating in its ohmic polarization region. The simulation results can be used to determine the catalyst content of cathode catalyst layer and the corresponding optimal thickness of PEM.展开更多
文摘Based on the requirement of water management for a direct methanol fuel cell, this paper analyzes qualitatively the mechanism of occurrence and development of a two-phase countercurrent flow with corresponding transport phenomenon in the PEM. A one-dimensional, steady state quantitative model of heat and mass transfer in internal volumetric ohmic heating porous media saturated by liquid and vapor phases is developed. The effects of capillarity, electro-osmotic drag and phase change are included. Two im-portant formulas to calculate the theoretical length of two-phase zone δ t and determine the critical criterion |?ω /γ |cr for dryout in PEM are deduced. By use of these two dimen-sionless parameters, dryout of PEM can be easily predicted. Theoretical temperature, pressure and saturation profiles within the two-phase region are obtained numerically, which can help to explore the performance of a DMFC operating in its ohmic polarization region. The simulation results can be used to determine the catalyst content of cathode catalyst layer and the corresponding optimal thickness of PEM.
