Study of Liquid-Cooled Fuel Cell Stack Uniformity considering Global and Local Characteristics under Air Starvation Conditions

Gas starvation significantly affects the uniformity of stack. To reduce this phenomenon, a three-dimensional, nonisothermal, and two-phase full-size liquid-cooled stack model was developed, and the characteristics of the global and local nonuniformities of oxygen and liquid water in the flow field, membrane temperature, and current density were analyzed under sufficient oxygen supply and three different degrees of gas shortage. Advanced uniformity evaluation criteria (AUEC) were proposed to evaluate the overall uniformity of the stack, which can effectively characterize the local high nonuniformity of the cell units and the differences between edge and intermediate cell units. The results showed that with a decrease in cathode stoichiometric ratio, the AUEC of oxygen, liquid water, membrane temperature, and current density all decreased. The increase in the cooling liquid velocity increased the AUEC of the membrane temperature and current density in the stack, and the AUEC increased further when the oxygen supply was sufficient. In addition, the improvement scheme of GDL gradient porosity was proposed, which can effectively improve the uniformity of each parameter in the stack.