The improvement in the degree of separation of a continuous-type concentric tube thermal diffusion column by means of a wire spiral, having a diameter equal to the annular spacing and inserted as a spacer in the annular region, was investigated both theoretically and experimentally. It was shown that the undesirable remixing effect could be effectively reduced and controlled by this type of wire and a substanial improvement in separation efficiency attained. Experimental results for the benzene- n-heptane and toluene-isobutyl alcohol systems quantitatively confirm the prediction of theory.