Numerical Calculation And Optimal Design Of Flow Field In Proton Exchange Membrane Fuel Cell

In terms of cooling methods,fuel cells can be divided into air-cooled fuel cells and water-cooled fuel cells.The air-cooled fuel cell combines the cooling function with the cathode channel,which effectively reduces the weight and complexity of the fuel cell system.In this thesis,the performance and optimization of air-cooled PEMFC are studied.Firstly,the mass transfer phenomenon and mechanism of PEMFC were studied.The factors influencing the performance of PEMFC were analyzed systematically from the aspects of temperature,humidity and oxygen distribution.The following conclusions can be drawn:in the air-cooled PEMFC,the saturation of water increases gradually in the direction of gas flow.The H₂mass fraction under the cathode rib is lower than that under the channel,while the H₂O mass fraction is the opposite.The average temperature under the cathode rib is lower than that under the cathode channel.The lowest temperature appears near the anode outlet.The design of cathode flow field has an effect on the performance of fuel cell.Secondly,the air-cooled flow channel plays an important role in the design of PEMFC.Based on the numerical model,the characteristics of temperature,relative humidity and oxygen concentration distribution were studied,and the effects of different cathode channel parameters on the performance of the battery were systematically discussed.It can be concluded that for air-cooled PEMFC,the relative humidity and temperature under the cathode channel are much lower,and provide oxygen for the reaction of air-cooled fuel cell.When the ratio of channel width to rib width is 1:1,the increase of channel width will lead to the decrease of cell performance and the increase of relative humidity and oxygen concentration distribution.Due to the influence of accumulated water,the relative humidity along the cathode channel increases gradually,and there is a regular fluctuation where the anode hydrogen flows along the vertical direction of the cathode channel.When the ratio is greater than 3,the increase of rib width and the decrease of channel width lead to the increase of drainage and mass transfer resistance.It is an effective way to improve the performance of air-cooled fuel cells by adding wavy features at the bottom of the channel.It enhances the mass transfer from the flow channel to the catalytic layer by providing the vertical velocity component of the gas flow.Finally,the performance of air-cooled PEMFC operating at different altitudes is studied.The models of air-cooled PEMFC at different altitudes were established.The power density,output voltage,output efficiency,oxygen concentration and water distribution of the air-cooled PEMFC were analyzed systematically from the current density and altitude.The following conclusions are drawn:with the increase of altitude,the battery power density,output voltage and output efficiency are getting lower and lower due to the decrease of working environment temperature,air density and atmospheric pressure.At the same altitude,with the increase of the current density of the battery,the reaction rate in the battery becomes faster,the consumption rate of reactants becomes larger,and the oxygen concentration in the cathode becomes lower,which leads to the decrease of the output voltage of the battery.The power density of the battery is decreasing.At the same altitude,the power density of the battery increases with the increase of current density.But with the increase of altitude,the increasing range is smaller and smaller.