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求翻译以下文章 The diffusion coefficient obtained by the present study is 6.2 9 10-7 cm2s-1 for Nafion 117 with the water molecules per sulfonate (k = 2–6 (H2O/SO3H)) under temperatures of 293–303 K. Yeo et al. [4] measured the diffusion coefficient of water in Nafion 115 with k = 22 and gave the following equation. D ¼ 6:0  103  exp 20:2  103=ðRTgÞ  ðcm2 s1Þ ð32Þ This equation gives 1.9 9 10-6 cm2s-1 at Tg = 303 K. Zawodzinski et al. [5] also show water diffusion coefficients in Nafion 117 as a function of k and give coefficients of 0.6 9 10-6 to 3.7 9 10-6 cm2 s-1 for k from 2 to 6 at 303 K. Nguyen et al. [6] investigated the diffusion coefficients of water in Nafion of different thicknesses under different temperatures. Nguyen et al. [6] showed that the diffusion coefficient for Nafion 117 with a water content of 2–6% of dry membrane weight is 1.5 9 10-7– 6.0 9 10-7 cm2 s-1 at 333 K. According to these reports, the diffusion coefficient depends on temperature and water content. The authors did not show a temperature dependence of the diffusion coefficient because they did not have sufficient data for the determination of this dependence. However, the author’s opinion is that the diffusion coefficient in the membrane depend on temperature as reported by those papers. Our simulation by the two-layer model can be improved by introducing a dependence on temperature and water content. The number of water molecules a carried by a proton moving toward the cathode is referred to as the electroosmotic drag coefficient [5]. We obtained 1.3 from the experiment under temperatures of 293–303 K and relative humidities of 40–80%. Zawodzinski et al. [5] reported that the electro-osmotic drag coefficient for Nafion 117 exposed to liquid water at 303 K is 2.5–2.9 with k = 22 and they suggest a substantial decrease in the electroosmotic drag coefficient as the water content is lowered. The difference in our result from theirs may result from the difference in the water contents in our element from that of Zawodzinski et al. Typical values of our results under steady state and transient conditions in the environment of 303 K, 60% are shown in Table 5. Under the steady state condition, water transported by both current and electroosmotic drag is cancelled by back diffusion. As a result, the dehumidifying capability at the steady state condition is zero. The dehumidifying capability under the transient condition shown in Table 5 is calculated to be 4.1 9 10-4 g s-1. From our estimation by simulation, the amount of water transported by electroosmotic drag is nearly cancelled by that from back diffusion. The electrolytic membrane of the element is covered by porous electrodes on both of its surfaces. Therefore, the actual area to transport water across the surfaces may be less than the area S of the membrane itself. We assume in this paper that the water transportation area across the
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