| The Proton Exchange Membrane Fuel Cell (PEMFC), also called as the Solid Polymer Fuel Cell(SPFC), is used in the fields of the aviation, aerospace, transportation, medicine and so on, because of the lower noises, the less pollution, the lower temperature start-up and the higher power conversion density. With the energy crisis and environmental problems exacerbated in the world, the PEMFC's importance has become increasingly obvious. The main direction of development is for the civilian power, small-scale power plants and other power supply, the output performance is an important indicator of research. The purpose and significance for this paper is to identify the impact of the fuel cell output characteristics of the relationship between factors and to improve the output performance of PEMFC, to provide gists for optimal design.Firstly, the influential parameters are divided into two categories through the analysis of PEMFC output performance:one is the control parameters, including temperature, humidity, pressure, the flux of reactant gas, and so on; the others are the non-control parameters that involved with the model factors, material factors, the structural factors and mass transfer factors etc. An evaluation of output indicators for PEMFC was put forward under the guidance of my instructor:the range of current density D (the less, the better) and the output voltage static slip S (the bigger, the better), at the same time, an example was used to verify the evaluation's validity.Secondly, the know ledges on the chemical kinetics and electrode thermodynamics were used to set up the relationship and model between the output performances of PEMFC and the major impact factors, such as the area of the proton exchange membrane, the proton exchange membrane thickness, the fuel cell operational temperature, and the anode/cathode reaction gas's pressure. The parameters were simulated by using MATLAB, and results showed that the parameters impact on the output were different in different current densities within the region, except the unilateralism.Thirdly, the major influencing factors were changing within a certain time, that according to the mathematical relationships and model between the main impact parameters and the PEMFC output performance, to adapt to environmental changes in the actual conditions. The results of the output performance showed that the best parameters under the constant current should be as follows:water content is 18.17, temperature is 368.14K, hydrogen pressure is 1.819 atm, oxygen pressure is 1.279 atm, and the best values of influencing factors should be:water content 14.12, the operation temperature 366.41K, the hydrogen pressure 1.655 atm, and the oxygen pressure 1.592 atm.Finally, a three-dimensional numerical model with direct channels have been built according to the PEMFC in the reality, and the model must include the electrochemistrical model, liquid model, mass transfer model and heat transfer model to meet the needs of PEMFC's simulation. Based on the needs used for the studying about the sizes parameters impacting on the output of PEMFC, a series of numerical models, with different ratios between channels width and shoulder, or the different depths of the channel, were established. Some different porous catalyst layers model were set up under the optimal flow channel to study the porosity impact on the output performance of PEMFC. The results obtained from the study for the simulation with PEM module in FLUENT shows:the optimal ratable value for the channel width and the shoulder width is 1:1, the porosity in catalyst layer is 50%, and the optimal value for channel depth is 0.4 mm. |
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