Study On Operation Characteristics Of Air-cooled Proton Exchange Membrane Fuel Cell

Fuel cells can convert chemical energy into electrical energy directly.It has the characteristics of low noise and no pollution reaction products.It is a new type of power generation technology,which helps to overcome the dependence on primary energy such as petroleum.At the same time,it is not limited by Carnot cycle and has high energy efficiency,so it is one of the most promising energy conversion devices.As the altitude increases,the output power of proton exchange membrane fuel cell（PEMFC）is limited by environmental factors,which affects its application in practice.Therefore,it is of great significance to study the operation characteristics of air-cooled PEMFC and its operation mechanism at high altitude.By establishing a three-dimensional simulation model of an air-cooled PEMFC,the internal physical field distribution characteristics of the PEMFC were analyzed from four aspects:oxygen concentration distribution,current density distribution,water concentration distribution and temperature distribution.After that,the dynamic response characteristics of the PEMFC were analyzed.The results show that increasing the cathode stoichiometry and operating pressure can effectively reduce the dynamic response time and improve the dynamic performance of the PEMFC.On this basis,the operation characteristics of air-cooled PEMFC at different altitudes were studied in detail,and the effects of inlet temperature,operating pressure and cathode stoichiometry on the performance of PEMFC were analyzed.The results show that the output performence decreases by 10.0%at the same inlet temperature when the altitude increases from 0 m to 4000 m,and it decreases by 25.5%when the inlet temperature decreases simultaneously with the increase of altitude.Increasing the cathode stoichiometry can increase the concentration of reactants,thus it can improve the performance and reduce the internal temperature difference of PEMFC.Finally,the temperature distribution characteristics of air-cooled PEMFC were studied from the perspective of heat transfer.A simplified three-dimensional simulation model of air-cooled PEMFC stack was established.The heat transfer capacity of three different heat transfer modes under steady-state conditions was calculated and compared.The temperature distribution characteristics of the stack were analyzed by introducing a temperature uniformity index（TUI）.The natural convection heat transfer and radiation heat transfer are much smaller than the forced convection heat transfer,which means that forced convection heat transfer is dominant.The stack temperature is increasing with the increase of current density,resulting in the worse uniformity of temperature distribution.The TUI of the central region of the stack decreases by 65.4%when the cathode stoichiometry increases from 60 to180 at 635 m A·cm^-2.Increasing the cathode stoichiometry can reduce the stack temperature effectively and improve the temperature uniformity of the air-cooled PEMFC stack.