| Summary: | 碩士 === 華梵大學 === 機電工程研究所 === 91 === The purpose of this research is to determine how the force convection generated by adding baffles affects the effect of efficiency of the fuel gas in the flow channel of a proton exchange membrane fuel cell. In addition, the different numbers of baffles and whether the flow channel is blocked by baffles are well-investigated. In this thesis, the commercial software CFDRC is utilized to simulate the 2-D half-cell in the cathode of PEMFC numerically by using finite volume method. In final, the distributions of the velocity and the concentration of fuel gases in the cathode and the percentage of mass flow rate of fuel gases flow into the diffusion layer are also analyzed in this research.
The results reveal that the max value of the mass flow rate of the fuel gases is noted in the diffusion layer when the baffles completely block the flow channel. The value of mass flow rate decreases with the increase in the gap distance. Because some fuel gases flow in the gap directly and pass the baffles, the force convection effect is attenuated as well. In the different ratios of the gap to the channel height (λ), the max value of velocity in the X direction component occurs when the λ is 0.05. The force reduces efficiently and avoids the breaking of the membrane when the fuel gases flow in the diffusion layer. In addition, in the aspect of the rate of oxygen reaction, the best performance of the oxygen reaction appears near the baffles when the baffles block the flow channel and the porosity (ε) of the diffusion layer is 0.7. The rate of oxygen reaction in the flow channel which blocked by baffle is better than that without baffle. If the baffles could be added in the flow channel, the oxygen flux in the catalyst layer under the baffle would become larger. Moreover, the maximum oxygen flux occurs in the catalyst layer at the first baffle. Besides, the oxygen flux in the diffusion layer under the baffle which at the middle of the flow channel decreases with increasing numbers of baffle.
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