Turbulence in Convection in Gases Between Concentric Vertical Cylinders

In a thermal diffusion apparatus consisting of two concentric vertical metal cylinders the temperature of the inner hot cylinder is measured for constant power input in the heater as a function of the pressure of the contained gas (${\mathrm{N}}_2$ or C${\mathrm{O}}_2$). The change from lamellar convection flow to turbulence produces sharply at a certain pressure a cooling which increases with further rise in the gas density. For this critical density the ratio of the remixing by convection to that by diffusion as well as the Reynolds numbers are computed. The latter are around 150; i.e., about $\frac{1}{10}$ the values found for flow through pipes. With increasing temperature difference a minimum value of the pressure for onset of turbulence is found. In order to insure lamellar convection flow in isotope separation by thermal diffusion, conditions should be adjusted so that the ratio of the two remixing effects is not more than $\frac{1}{10}$ these critical values.