Isotope Separation by Single-Stage Sweep Diffusion Process

Abstract

A theoretical treatment of single-stage sweep diffusion process is presented. Several workers have analyzed the sweep diffusion process by assuming a relation governing the diffusion fluxes, or by approximating the boundary conditions of the concentrations. The model adopted in our present theory consists of a horizontal diffusion pipe and two mixing chambers attached to each end of the pipe; these chambers act as the charge and discharge systems of the stage. The boundary conditions of the diffusion equations are given by mass balance considerations around the chambers, so that the separation factor and the diffusion fluxes can be estimated in terms of three flow rates of streams: feed, separating agent, product or waste. In the case of nitrogen isotope separation with CO2 gas as separating agent, the calculated values of fluxes agree very closely with the experimental results. However, the magnitudes of the separation factor minus one obtained experimentally are about 16% smaller than the corresponding theoretical values. This discrepancy would appear attributable to the presence of some convective mixing through the diffusion pipe.