Numerical analysis of flow of binary gas mixture with large mass difference in rotating cylinder.

Abstract

A numerical analysis is presented of the flow of a binary gas mixture of UF6 and N2 in a rotating cylinder. The equations for flow and the diffusion equation are solved simultaneously for the binary mixture in static state, taking account of viscosity and compressibility, using a modified version of the Newton method, commonly applied to rotating fluid flow. An appropriate model is assumed for a centrifuge provided with scoop and baffle plate. Computations are carried out with the N2 to UF6 mixing ratio adopted as parameter. At small values of mixing ratio, the pressure distribution of UFC in the radial direction is little influenced by the presence of N2. The N2 pressure distribution is close to that at equilibrium of N2 itself in zones inside cylinder of relatively slow gas travel. In the zones of faster gas travel, conversely, the N2 pressure distribution deviates from that of its equilibrium and approaches that of UF6. The pressure distribution of UF6, on the other hand, is strongly influenced by the presence of N2 when the mixing ratio is above 0.2. The resulting radial distribution along a section close to the exit scoop presents a peculiar concave configulation with a shallow valley appearing in the intermediate zone, and this significantly lowers the concentration of UF6 extracted through the scoop. The separation efficiency obtained between the two gases is extremely low, but this is due to the mass flow rate having been chosen to optimize the separation efficiency between UF6 isotopes.