Thermal gradient tube species

Consider a system which is made up of two bulbs connected by a long, narrow tube into this system ia placed a mixture of A and B. If one bulb is maintained at a low temperature Ti and the other at a high temperature T%, there will be a tendency for A to move toward the cold region and B to the hot region (if kr is positive). This tendency for the two species to separate from one another creates concentration gradients, which in turn cause ordinary diffusion, which opposes the process of thermal diffusion. A steady state condition is ultimately established, characterized by the fact that there is no average relative motion of A and B (that is (va — vB) — 0). Hence from Eq. (59) one obtains for diffusion in the z direction only... 

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