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Analytical expressions for the non steady separation factor of an isotopic multicomponent mixture in a thermal diffusion column are given. The results, which are appropiate for column operation at total reflux and cover the real case in which small non active end volumes are present, show a simple exponential rising of the logarithm of the reduced separation factor independent of the initial mixture composition. This fact is confirmed by experimental transient data previously reported by Brun et al. and by new experimental work presented here. It is shown that the relative variations of the relaxation time with the hot wire temperature and with the operation pressure are just those predicted by the Furry, Jones and Onsager theory. It is concluded that two experimental operations: steady-separation vs pressure and non-steady separation vs time, and the use of FJO theory will allow us the qualitative prediction of the column operation in the usual temperature and pressure range in laboratory operation more...

A hot wire thermal diffusion column with a variable non-active volume has been constructed, The experimental results for the relaxation time as a function of the non-active volume are compared with the theoretical predictions. The good agreement obtained suggests that-our transient formulation can confidently be used to determine the experimental values of the column coefficients. The relaxation time measurements do not permit to distinguish between the active and non-active parts of a column, and the remixing coefficients K c and K d can be experimentallv obtained without an explicit knowledge of the non-active volumes in the column. more...