直接甲醇燃料电池气、液相流动数值模拟

SIMULATION OF GAS-LIQUID FLOW IN DIRECT METHANOL FUEL CELLS

本文建立了直接甲醇燃料电池(DMFC)的二维两相模型,并重点研究阳极的两相流动和质量传递.模型考虑甲醇串流现象,定量计算了在不同电流密度下甲醇串流量的大小及其对电池工作性能的影响;模型中提出求解气、液单相流速的方法,并分别研究气、液流速对物质传递和电池性能的影响。定量分析发现:由甲醇串流产生的寄生电势导致实际开路电压值远低于理论值;在大电流密度下扩散层和催化层内的气相体积分数非常大,阻碍了液相燃料向催化层扩散,成为制约电池性能的关键因素;扩散层和催化层内存在气、液两相的反向流动,且气、液相速度分别有利于排出生成气体并推动液体燃料到达催化层;减小多孔介质的扩散率将削弱对流,恶化电池性能。

A two-dimensional two-phase model considering methanol crossover has been established and the phenomena of two-phase flow and mass transfer in the anode are paid special attention to in this paper. The model takes measures to calculate gas and liquid velocity separately and investigates the effect of gas and liquid velocity on mass transfer and fuel cell＇s performance. Quantitative investigations show results below： Parasitic voltage resulted from methanol crossover makes the practical open circuit voltage much lower than theoretical value. Since gaseous volume fraction in diffusion layer and catalyst layer is very high under high current density, the generated gas may block the transfer of liquid fuel and become key factor that hinders the performance of fuel cell. The gas-liquid counter flow in diffusion and catalyst layer can help vent the generated CO2 and drive liquid fuel to catalyst layer. Lower permeability of the porous media weakens gas-liquid counter flow and deteriorates the performance of the fuel cell.