The equation for predicting the degrees of separation for deuterium recovery from the H2–HD–D2 system using thermal diffusion in single-column, double-column and triple-column devices are derived. The column number effect on separation efficiency with a fixed total sum of column heights is then investigated. Considerable improvement in recovery can be achieved in multi-column devices, instead of a single-column device with the column height equal to the same total sum of column heights, especially for the cases of higher flow-rate operation and larger total sum of column heights.
