| High efficiency of fuel cell and its environmentally friendly characteristic has brought it a great application prospect in the field of portable power. Compared with portable power, traditional fuel cells are too bulky. In order to simplify traditional fuel cell system, air-cooled fuel cell stack can be a feasible way to solve the problem. Air-cooled stack can simplify the cooling system, air compressor, air pump system, humidification system and etc which make fuel cell more convenient in regard of the application on portable power. The simplification of the system brings about major different operating condition between air-cooled stack and traditional stack., for this reason, discussing heat and mass transfer mechanism to optimize the flow field of the stack and the structure of MEA, simplifying the system while maintaining output of the high performance of stack are very necessary. The main research contents and results are as follows:(1) Analyze the working condition of air-cooled stack. Discuss the heat and mass transfer mechanism. Build the heat and mass transfer balance model.(2) according to the analog computation of the model, within the operating temperature that range from30℃to70℃under the air-cooled stack normal working condition, The heat dissipation primarily vie air forced convection and radiation heat as well as natural convection heat dissipation are far less than the heat capacity of air forced convection. This differs from the description made by the literature.Meanwhile when the stack are working under the condition of constant temperature., within the allowed range of the strength of the stack and contact resistance, appropriately increasing aperture ratio and length-width ratio of the flow field can enhance the heat dissipation efficiency of the air-cooled stack.. When the aperture ratio of the stack between 60% to 70% and the section of flow field between 1.4 to 1.8. Besides the water retaining capacity of GDL is concerned with the thickness and aperture ratio of GDL. When GDL is thicker, its aperture ratio will be lower and its water retaining capacity will improve. On condition that guarantee the transfer of oxygen, the thickness of GDL should be 0.7mm and its aperture ratio is 60% when operating at 500mA/cm2 and 0.6V.(3) Study different types of cell which contains different flow field, structure and MEA. The performance of the cell will improve with the increase of the thickness of GDL, when it increases to its maximum value 0.6mm, then it will degrade with the increase of the thickness of GDL. Water repellent treatment to GDL can not only help to drain off water from conventional cell but also can enhance the capacity of unhumidified air-cooled stack. When hydrophobic degree of GDL reaches to 40%, the performance of the cell can achieve to maximum level. The ability of resistance to dry of WUT composite membrane is much better than that of Nafion membrane. Under the same dry condition, performance of the cell using composite membrane is better than cell using Nafion membrane.(4) Optimization research to operating condition of air-cooled stack draw a conclusion that the optimum operating temperature is 65℃and that the performance of experimental air-cooled will increase along with the increase of air volume., when increasing to 2.68m3/min, the performance of cell is the best, when air volume continue to increase, the performance of the cell will degrade, because cooling air will take excess water from the cell. Anode using dead-end model can increase water content, thereby improving performance of the cell and saving fuel. |
