Diffusion and dispersion in steady counterflow: a method for the separation of gases using enhanced mass transport in oscillatory flow

Diffusional separation of molecules or isotopes of different molecular weights is markedly enhanced if the diffusion takes place against a continuous, low-velocity current of the carrier fluid. Theoretically, the separation may become infinite; the mass transport, however, is markedly reduced. The reduction of mass transport can be effectively counteracted by enhancing the rate of diffusion using tuned, axial oscillations of the carrier fluid. Mass transport is enhanced by as much as 4 to 6 orders when diffusion takes place in an oscillating medium. Combining counterflow with tuned, axial oscillations generates a mass transfer that has promising features. (1) It can be applied to gases or liquids; only gaseous separation is discussed in some detail in this paper. (2) It may be used to enrich either the lighter or the heavier of a mixture of molecules. (3) The yield and separation ratio can be controlled over a wide range by adjusting the operational settings of the controlled variables, such as rate of feed input, rate of carrier input, and rate of counterflow. (4) The separation ratio is fairly high even when the ratio of the molecular weights of the gases or isotopes is close to unity. Particular emphasis is put on enhancing the performance by testing the maximal enhancement of mass transport that can be achieved in a particular pipe configuration and by reducing the expected operational costs.