Rotating the tubes oppositely in a transverse-flow concentric-tube thermal diffusion column inserted as a spacer in the annular region with a wire spiral, having a diameter equal to the annular spacing, was investigated. Equations of the optimal tube speed of rotation for maximum separation and maximum output have been derived. Instead of using the stationary column without wire spiral, considerable improvements in performance are obtainable if a rotated wired column is employed operating at the optimal tube speed of rotation to create the desirable cascading effect while still suitably suppressing the undesirable remixing effect. (c) 2006 Elsevier B.V. All rights reserved.