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siximeiwen铜虫 (正式写手)
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[求助]
有没有人可以解释下扩散和弥散的区别？ 已有1人参与
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2楼2011-12-12 22:16:19
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3楼2011-12-13 09:14:03
静水四叶草
金虫 (小有名气)
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4楼2011-12-13 10:46:12
【答案】应助回帖
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扩散diffusion，弥散dispersion Diffusion and dispersion are different modes of mass transfer in that the mechanisms behind them are different. Diffusion is the spreading out of material that occurs due to the random thermal motion of molecules, and is characterized by molecules behaving as "random walkers". In order to understand dispersion, consider a convective flow superposed over the diffusion. If the flow velocity is uniform everywhere (i.e. "plug flow"  , then molecules at different places in the flow will move with the same convective velocity, and it is only diffusion rate which will differentiate between them. However, now consider a flow in which gradients exist, for example fully developed pipe flow. The fluid at the center of the pipe is moving much faster than the fluid close to the walls. If there is diffusion in the radial direction, then molecules can hop over from one streamline to the next, and thereby will be transported over different distances due to the difference in velocities. This smearing out (or being transported over different distances) caused indirectly by diffusion (in the radial direction) is the physical interpretation of dispersion. Surprisingly, the amount of dispersion reduces with increasing diffusion coefficient. This is because, then, the molecules will just be hopping from one streamline to another constantly and will not get "enough" time to be transported far from each other. The above physical model of dispersion is explained beautifully in the book "Analysis of Transport Phenomena" by William M. Deen. You should have a look, if possible!——QUORA http://www.zhihu.com/question/23914350/answer/55768081 来源：知乎 |
5楼2016-03-25 09:08:55