Mass transfer through a stationary second component

Mass transfer through a stationary second component 

In several important processes, one component in a gaseous mixture will be transported relative to a fixed plane, such as a liquid interface, for example, and the other will undergo no net movement. In gas absorption a soluble gas A is transferred to the liquid surface where it dissolves, whereas the insoluble gas B undergoes no net movement with respect to the interface. Similarly, in evaporation from a free surface, the vapour moves away from the surface but the air has no net movement. The mass transfer process therefore differs from that described in Section 10.2.2. 

The concept of a stationary component may be envisaged by considering the effect of moving the box, discussed in Section 10.1, in the opposite direction to that in which B is diffusing, at a velocity equal to its diffusion velocity, so that to the external oh iver B appears to be stationary. The total velocity at which A is transfeired will then be incfeased to its diffusion velocity plus the velocity of the box. 

For the absoiption of a soluble gas A from a mixture with an insoluble gas B. the respective diffusion rates are given by  

The corresponding bulk flow of A must be C /C times tiiat of B, si that the gas moves en masse. 

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For mass transfer through a stationary second component ... 

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