© 1959 by Oxford University Press
ON THE SEPARATION OF GAS MIXTURES BY SUCTION OF THE THERMAL-DIFFUSION BOUNDARY LAYER
( (The University of Michigan Ann Arbor, Michigan) )
This paper discusses the formation and characteristics of the boundary layer of thermal diffusion existing along the surface of a heated wall over which flows a mixture of gases of unequal molecular weights. Due to the existence of a temperature gradient in the boundary layer, a thermal-diffusion flux is set up such that the lighter gas tends to move to the hotter region and the heavier gas to the colder region. When the temperature of the surface is maintained at a much higher level than that of the free stream, the concentration of the lighter gas increases monotonically from its free-stream value at the outer edge of the boundary layer to a maximum value at the plate.
The existence of an extremely high temperature gradient makes it possible to obtain significant diffusive separation of gas mixtures in the boundary layer of a laminar flow. From this consideration a new method of separating gas mixtures by suction of the thermal-diffusion boundary layer was conceived. An analysis of the thermal-diffusion boundary layer is made, using a flat plate with constant suction as a model and assuming that the concentration of the lighter gas is much smaller than unity. The strong stabilizing effect of suction on the laminar flow is discussed briefly. A limiting ratio of suction against free-stream velocity for the maintenance of laminar flow is derived. An estimation of the rate of attaining the equilibrium-concentration profile is also made.