阴、阳极加湿程度对PEMFC内部传质的影响

Effects of humidifying level of cathode and anode gas on mass transfer in PEMFC

为了研究常规流场下阴、阳极增湿程度对电池内部水分布、传递、膜性能及水拖曳系数等的影响,对PEMFC进行二维建模,应用控制容积法对控制方程进行离散,然后求解,得到了电池内部水和反应气浓度、速度分布、膜中电流密度、电势分布及膜中水分布,考察了气体不同增湿程度对质子交换膜电导率及电池内部传质的影响.结果表明,PEMFC中水综合拖曳系数随着阳极加湿程度的增加而增大,随阴极增湿程度的增加而减小,但阳极增湿对水综合拖曳系数的影响比同增湿程度下阴极增湿对水综合拖曳系数的影响大得多.同时,随着阳极加湿程度的升高,质子交换膜(PEM)电导率急剧升高,而阴极加湿程度对PEM电导率的影响只是停留在较小的电流范围之内.故PEMFC在小电流密度工作时,应该使阳极气体充分增湿;而在大电流密度工作时,应该适当降低阳极的增湿程度以降低阴极两相流的机会,从而改善阴极的传质状况.

A two-dimensional model of PEMFC with conventional flow field was established and the partial differential equations were solved based on the control-volume method. The effects of humidifying level on membrane conductivity and mass transfer were investigated. The numerical results indicated that total water drag coefficient increased when humidification in anode increased, and membrane conductivity was largely improved when humidification in anode was enhanced. Total water drag coefficient reduced when humidifying level in cathode increased. Humidification in anode was more important than that in cathode where the humidification effect was limited only to relatively low current density. The anode gas should be humidified as much as possible, when PEMFC operated at low current density. It is advisable to decrease the humidifying level of anode gas when operating at high current density to avoid two-phase flow in cathode so as to improve mass transfer.