Experiment And Numerical Simulation Of Temperature On PEM Fuel Cell Performance

As an energy conversion device,proton exchange membrane(PEM)fuel cell due to its unique advantages such as high efficiency,zero pollution,so,has been considered to be an excellent alternative energy sources.Currently,PEM fuel cells have been paid enough attention in the automotive sector,and gradually move towards their rightful place.PEM fuel cells have the ad-vantages of easy water and heat management,which make them get much more attention,but immature technology hinder their application in the market.In this thesis,the effects of temperature on PEM fuel cell performance were studied by experiment,and the temperature and flow reduction reaction characteristics which took place in PEM fuel cell were studied by simulation.The results have some reference values on the design and development of PEM fuel cells.In this thesis,the history of fuel cell development,strengths and weaknesses of fuel cells and its application in practice were summarized.The components of PEM fuel cells,working principle,development and the research progress of PEM fuel cells were introduced.Then the thermodynamic theory,kinetic theory,calculation method of the amount of reactive gas and the efficiency of PEM fuel cells were summarized,and fuel cell test system was described in detail.In the end,the fuel cell systems operating methods and data processing methods were summarized as well.Firstly,the v-i characteristic curve and AC impedances of PEM fuel cell were tested by the fuel cell test system.The equivalent circuit method was used to obtain the equivalent circuit element of PEM fuel cell.The effects of hydrogen flow on PEM fuel cell performance were also analyzed.The results showed that the performance of the fuel cell was improved with the temperature increasing,however,when the optimum reaction temperature was exceeded,too much water existed in the cell whith hindered the proton transfer and resulted in a decline in PEM fuel cell performance.The increase of hydrogen flow could improve the performance of the fuel cell in a certain extent,but it was not obvious.When hydrogen flow reached a certain limit,the performance of fuel cell was almost not changed any more,the optimal value of the hydrogen content was obtained.Secondly,in order to analyze the influence of cell temperature better,three-dimensional simulation was carried out in which the setting of materials,heat exchange between the various parts of the cell and the thermal convection with air were added,then the results of simulation were compared with the test results.The temperature difference due to produced byinternal reaction of various parts of the cell had a great impact on the performance of PEM fuel cell.Based on molecular dynamics and thermodynamics,PEM fuel cell model was built by using COMSOL coupled with physical field.Based on the analysis of the data obtained in the simulation,it can be concluded that the temperature of floe channel gradually decreased with the gas flow,and the location of highest cell temperature gradually moved close to the cathode.When the cell temperature changed from 313K to 353K,the temperature rise had the same trend amony anode channel,the membrance and cathode channel.Finally,multi-physics fields coupling analysis software was adopted to establish the single cell 3D model of fourchannelsstructure of flow field.when the working voltage is 0.5 V,porosity were 0.2,0.3,0.4 and0.5 respectively,PEM fuel cells were numerical simulated.The simulation results presented the variations of the membrane current density,cathode oxygen concentrationand the center ofcathode flow channel pressure.Analysis showed that the increase of the permeability could,lead to the increase of the membrane current density of PEM fuel cells,and the change trend of membrane current density was parabolic.Improving the gas mass transfer inside the fuel cellsand accelerating the electrochemical reaction rate could improve the output performance of the fuel cells.