Equations have been derived for the optimum wire angles of inclination for maximum separation, maximum production rate and minimum column height in the Frazier scheme of concentric-tube thermal diffusion columns with a tight fitting wire spiral, having a. diameter equal to the annular spacing, and wrapped on the entire inner tube. considerable improvement in, performance is obtained when a Frazier scheme Is operated At the optimum corresponding wire angle of inclination, especially for the scheme of high column number.