本文以平板型Frazier熱擴散塔裝置為基礎，在塔高總和固定下，塔高以等差遞變與等塔高之裝置對分離效果之影響加以分析討論。本文中所討論的進料質量濃度分率在全濃度範圍下的三種範例系統分別為，苯-正庚烷二成份系統、重水系統與重水中回收重氫系統。等塔高與等差遞變塔高之Frazier裝置的分離度公式已於本文中推導出，利用先前文獻之實驗數據並依照各系統作適當之計算處理，可得各系統於等塔高與等差遞變塔高Frazier裝置之分離度值，並篩選最佳分離度之值，再加以整理成最佳裝置設計之經驗式，且在最佳等差係數 值大於零時，即等差遞增之塔高裝置，具有最佳之分離度值；至於 小於零時所呈現之分離效果雖然比等塔高裝置佳，但仍比 大於零時的分離效果差。三種範例系統所得之計算數據皆為等差遞變塔高之裝置具有最大之分離度值，其結果令人相當滿意；且藉由範例系統之計算可加以印證本文中熱擴散塔的分離理論可適用於任何具有平衡關係之液態混合物系統。 First, the effect of the number of columns (or the uniform column height) on the separation efficiency in thermal diffusion columns of the Frazier scheme at fixed sum of column height has been investigated. The equations for predicting the optimum number of columns and corresponding maximum separation were derived. The numerical examples for the separation of benzene-n-heptane system and water-isotopes mixture, as well as the recovery of deuterium from water-isotopes mixture, have been illustrated. Considerable enrichment in separation is obtainable if the number of columns (or the uniform column height) in a Frazier scheme is properly assigned for a certain flow-rate operation. Next, in addition to the device of optimal number of columns, the modified Frazier scheme, in which the column heights are also varied at a constant increment, has been further investigated. The equations of the optimal column number, optimal difference of column height and the corresponding maximum degree of separation in the modified Frazier scheme were derived by employing the method of variable univaniant. The numerical examples given before were also employed and calculated. It is found that as the flow rate increases, the optimal column number increases, while the optimal increment of column height decreases. Considerable improvement in separation can be achieved by employing the modified Frazier scheme rather than using the classic Frazier scheme, as well as even using the one only with the optimal column number.