本研究旨在探討於成本固定下，順流式Frazier型平板熱擴散塔裝置中三項設計條件(傾斜角、板間距及長寬比)對分離效率之影響。結果發現三項設計條件無法同時存在，甚至沒有同時存在兩個最佳之設計條件。至於每一單獨項的最佳設計條件計算公式，以及其對應的最大分離度的計算公式，可順利推導而出，而以其他兩項設計條件為參數。文中並列舉兩個範例，利用其結果來比較三項最佳設計條件下的分離效率。結果發現：對分離苯-正庚烷混合物以及分離水同位素混合物而言，組立一順流式Frazier型平板熱擴散塔得最佳方法為，採取最佳的板間隙，並令傾斜角、長寬比以及塔數在不違反常態之下盡量加大。 The effect of three design conditions ( angle of inclination, plate spacing and plate aspect ratio) on thermal diffusion performances in the cocurrent-flow Frazier scheme at fixed expense have been investigated. The equations for predicting each optimal design condition for the corresponding maximum separation have been derived with other two design conditions as parameters. However, there are no two optimal design conditions existing simultaneously for the best performance. The limitations of practical applications were also delineated. Two numerical examples were presented for illustration, and the performances obtained at each optimal design condition were compared. It was found that the best way to construct a cocurrent-flow Frazier scheme is designed at the optimal plate spacing with larger inclination, larger plate aspect ratio and smaller number of columns.