The enrichment performances of heavy water in various concentric-tube thermal diffusion columns, such as open, wired and rotated wired devices, have been compared with different flow-rate range operations. It was found that the operation with a wire spiral inserted in the annular spacing and with tubes rotated in opposite directions will reduce the remixing effect and enhance the cascading effect, respectively, resulting in improved the separation. (C) 2004 Elsevier B.V. All rights reserved.