In some other mass 在其它一些诸如 transfer operations such浸取和吸咐操作 as leaching and 中发生的是不稳 adsorption, unsteady- 定扩散,随着过 state diffusion takes 程趋于平衡,扩 lace, and the gradients pl and fluxes decrease with散组分的浓度梯 time as equilibrium is度和通量随时间 approached. 而降低
In some other masstransfer operations such as leaching and adsorption, unsteadystate diffusion takes place, and the gradients and fluxes decrease with time as equilibrium is approached. 在其它一些诸如 浸取和吸咐操作 中发生的是不稳 定扩散，随着过 程趋于平衡，扩 散组分的浓度梯 度和通量随时间 而降低
Although the usual cause of 虽然扩散的一般 diffusion is a concentration 原因是浓度梯度,但 gradient, diffusion can also be 能动梯度也能引起扩 caused by an activity gradient. as in reverse osmosis, by a 散如反渗透过程,压 pressure gradient, by a 力梯度、温度梯度和 temperature gradient,orby外场力都可引起扩散, the application of an external如离心分离。 force field, as in a centrifuge
Although the usual cause of diffusion is a concentration gradient, diffusion can also be caused by an activity gradient, as in reverse osmosis, by a pressure gradient, by a temperature gradient, or by the application of an external force field, as in a centrifuge. 虽然扩散的一般 原因是浓度梯度，但 能动梯度也能引起扩 散如反渗透过程，压 力梯度、温度梯度和 外场力都可引起扩散， 如离心分离
Molecular diffusion induced由温度引起的分子 by temperature is thermal 扩散称为热扩散, diffusion, and that from an 由外场力引起的扩 external field is forced 散称为强制扩散。 diffusion. Both are 这两种扩散方式在 uncommon in chemical 化学工程中并不常 见。本章仅讨论由 engineering. Only diffusion 浓度梯度引起的质 under a concentration 量扩散。 gradient is considered in this chapter
Molecular diffusion induced by temperature is thermal diffusion, and that from an external field is forced diffusion. Both are uncommon in chemical engineering. Only diffusion under a concentration gradient is considered in this chapter. 由温度引起的分子 扩散称为热扩散， 由外场力引起的扩 散称为强制扩散。 这两种扩散方式在 化学工程中并不常 见。本章仅讨论由 浓度梯度引起的质 量扩散
Diffusion is not restricted 扩散并不局 to molecular transfer限于分子通过固 through stagnant layers体或液体停滯膜 of solid or fluid. t also的传递。当不同 takes place when fluids组成的流体相混 of different compositions合时也会发生扩 are mixed 散
Diffusion is not restricted to molecular transfer through stagnant layers of solid or fluid. It also takes place when fluids of different compositions are mixed. 扩散并不局 限于分子通过固 体或液体停滞膜 的传递。当不同 组成的流体相混 合时也会发生扩 散