MASS TRANSFER IN THE ENTRANCE REGION OF A CIRCULAR TUBE.

A solution in the form of an asymptotic expansion is obtained for the problem of mass transfer in the entrance region of a circular tube or flat channel for arbitrary hydrodynamically-developed velocity profile and arbitrary dependence of the diffusion coefficient on the coordinate perpendicular to the flow. Boundary conditions of the first, second and third kind are considered. The results of the analysis are compared with known approximate and numerical solutions of similar problems.