| Summary: | 碩士 === 國立交通大學 === 機械工程系 === 90 === The primary concern of this study deals with the prediction of fuel cell performance with variable porosity of gas diffuser layer owing to the presence of liquid water in the gas diffuser layer. The half-cell model comprising expressions for the oxygen mass fraction distribution in the gas channel, gas diffuser, and catalyst layer, and current density and membrane phase potential in the catalyst layer and membrane derived from oxygen transport equations and Ohm’s law for proton migration is investigated with the finite-difference scheme numerically.
First, the gas diffuser layer was divided into four, five, and six parallel layers defined by different porosity coefficients to investigate that whether the cell performance would become if we increase the number of parallel layers of gas diffuser layers. The results reveal that the increase of parallel layers of gas diffuser layers has insignificant effects on cell performance. The limiting current density increases as the porosity of gas diffuser layer is increased.
Second, five different continuous models of porosity distribution are demonstrated. It is found that the differences of oxygen mass fraction among of five models become significant as the surface overpotential increases. At = 0.36, the difference between the highest and lowest current density can reach 16 of the highest one and the difference between the highest and lowest membrane phase potential is 24 of the lowest one. The limiting current density increases as the porosity of gas diffuser layer is increased. The peak power density occurs at larger current density as the porosity of gas diffuser layer is increased. The higher the porosity of gas diffuser layer is, the better cell performance can be obtained.
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