| Water management in PEMFC is an important problem,flooding significantly affect the performance of fuel cell. To improve the water flooding in the flow channels of PEMFC, a new air distribution method with a secondary inlet is developed to improve the cell performance.Firstly, the effects of humidification temperature of air on the performance are experimental studied. A single PEM fuel cell with active area of 25cm2 of MEA is tested under constant current density, the results showed that compared to humidification temperature of hydrogen, the humidification temperature of air is more important to the stability of PEM fuel cell. Through monitoring the cathode pressure drop, the results showed that cathode pressure drop could be used to judge water content in cathode flow channels, when the humidification temperature is low, there is a positive relation between cathode pressure drop and cell voltage, and when water flooding happens, the cathode pressure drop and cell voltage is negative related.In general, liquid water would appear at the second half of flow fields, it is bad to the cell performance, because the mass transfer loss lower the cell voltage. To solve this problem, a secondary inlet gas distribution method is developed. The whole air flow rate do not change, while one part of air without humidification directly get into the cell through the secondary inlet to improve the flooding at the second half of flow channel, to improve the cell performance.A two-dimensional model is used to study the effect of new gas distribution method, and the results showed that the new method is able to improve cell performance, especially under the higher current density. The effect of position of secondary inlet and the flow rate of dry air are also studied: the best position would at the 30% of whole channel length, when the dry flow rate is 60%~70%, the cell performance is best.A single PEM fuel cell with active area of 90cm2 with secondary inlet is experimental studied, the results showed that the position of secondary inlet is 30%, when the cell performance is the best, as the distance gets long, the secondary inlet can not improve the cell voltage, the best flow rate of dry air is related to current density, at higher current density, the higher flow rate is better, but as the flow rate get high, the voltage is unstable. The experimental results showed that when the position is 30%, the dry air flow rate is 70%, the cell voltage is the best, and this is same with the results of model. |
