Effect of changes in feed rate and cut on circulating flow within thermal diffusion column for isotope separation

A two-dimensional axisymmetric convectional flow field of an isotope separating thermal diffusion column with continuous feed and draw-offs is analyzed through the Newton iterative numerical solution of the equations of change without the Boussinesq approximation. Computations are performed for Ar gas within an inner hot radius of 0.2 mm and an outer cold radius of 5 mm, between which the temperature differs by 300 K. The rate of feed F, supplied into the middle point of the column, is varied from 1 to 5 cm3/s, while the cut θ, or the ratio of the upper drawing-off to feeding rates, from 0.1 to 0.9. Comparison of flow vectors, temperature and density profiles among various sets of (F, θ) makes it clear that the flow fields agree with one another for the same value of the total transport ; that is, θFρc (ρc: feed gas density) in the upper section and -(1-θ) ρc in the lower section of the column. Observations on the mass flow vectors near the feed slit lead to the finding that the multiplicative effect of separation cannot be expected in the column with the inner radius rc of 5 mm at the feed rate F exceeding 2 cm3/s(i.e F/(ΔTrc4) > 0.1 [1/(s · K · cm)]), because the feed flow interrupts the whole-length circulation of the natural convection. (author)