第17章相际扩散与传质原理 概 Diffusion is the: movement 扩散是一种 under the influence of a 在物理驱动下单 physical: stimulus, of an 组分通过混合物 individual component through 的运动。扩散最 a mixture. The most common cause of diffusion is a 通常的原因是扩 concentration gradient of the散组分浓度梯度 diffusing: component 的存在
第17章 相际扩散与传质原理 概 述 扩散是一种 在物理驱动下单 组分通过混合物 的运动。扩散最 通常的原因是扩 散组分浓度梯度 的存在。 Diffusion is the movement, under the influence of a physical stimulus, of an individual component through a mixture. The most common cause of diffusion is a concentration gradient of the diffusing component
concentration浓度梯度驱使扩 gradient tends to move散组分朝着使浓 the component in such a 度均匀化的方向 direction as to equalize 扩散,从而使浓 concentrations and destroy the gradient. 度梯度趋于消失
A concentration gradient tends to move the component in such a direction as to equalize concentrations and destroy the gradient. 浓度梯度驱使扩 散组分朝着使浓 度均匀化的方向 扩散，从而使浓 度梯度趋于消失
B::When: the gradient: is 当不断地向 maintained: by constantly supplying the: diffusing 高浓度一端提供 component: to: the high 扩散组分,从低 concentration: end::of the 浓度一端除去扩 gradient and: removing: it at the: ow: concentration 散组分时,扩散 end, there: is: a: steady-state组分便具有稳定 flux: of the diffusing 的传质通量。这 component:: This is 就是许多传质操 characteristic: of many mass-transfer: operations 作的特点
❖ When the gradient is maintained by constantly supplying the diffusing component to the highconcentration end of the gradient and removing it at the low concentration end, there is a steady-state flux of the diffusing component. This is characteristic of many mass-transfer operations. 当不断地向 高浓度一端提供 扩散组分，从低 浓度一端除去扩 散组分时，扩散 组分便具有稳定 的传质通量。这 就是许多传质操 作的特点
For example, when ammonia is例如,当在填料塔 removed from a gas b 中用水吸收气体中 absorption in water in a packed的NH3时,在塔内 column, at each point in the 的任意一点上,在 column a concentration gradient气相浓度梯度的驱 in the gas phase causes ammonia使下,NH3由气相 to diffuse to the gas-liquid 主体扩散至气~液 interface, where it dissolves,and界面,在界面上溶 a gradient in the liquid phase 解,然后,在液相 causes it to diffuse into the bulk浓度梯度驱使下, liquid 扩散至液相主体
例如，当在填料塔 中用水吸收气体中 的NH3时，在塔内 的任意一点上，在 气相浓度梯度的驱 使下，NH3由气相 主体扩散至气～液 界面，在界面上溶 解，然后，在液相 浓度梯度驱使下， 扩散至液相主体。 For example, when ammonia is removed from a gas by absorption in water in a packed column, at each point in the column a concentration gradient in the gas phase causes ammonia to diffuse to the gas-liquid interface, where it dissolves, and a gradient in the liquid phase causes it to diffuse into the bulk liquid
In stripping a solute from a 当从吸收液中 解吸溶质时, liquid the gradients are 浓度梯度与吸 reversed: here diffusion 收过程相反 brings solute from the bulk在此,扩散作 liquid to the interface and 用使溶质从液 相主体移至界 from there into the gas 面,再从界面 phase. 移至气相
In stripping a solute from a liquid the gradients are reversed; here diffusion brings solute from the bulk liquid to the interface and from there into the gas phase. 当从吸收液中 解吸溶质时， 浓度梯度与吸 收过程相反。 在此，扩散作 用使溶质从液 相主体移至界 面，再从界面 移至气相