本研究是將非牛頓流體中具有剪稀薄現象之液體作為工作流體使用於二行程套管加熱器中，而加熱器設計為圓形管加裝一可忽略熱阻之隔板，使之成為一組固定外壁溫度具有迴流裝置之圓柱同心套管熱交換器，此系統所推導出的數學模型是屬於共軛格拉茲問題(conjugated Graetz problem)，以分離變數法並利用正交展開方法(orthogonal expansion technique)，探討不同的剪稀薄係數與迴流效應於二行程套管間的熱傳效率之影響，其結果與單行程系統比較效率上的改善，也與實驗結果做比較了解理論的準確性。 結果顯示，出口溫度與納塞數隨剪稀薄係數降低而變小，在格拉茲數大時，其熱傳效率有明顯改善。而預混效應及滯留時間效應亦是影響熱傳效率的兩個因素，並討論兩者對系統的影響。不同的剪稀薄係數及迴流比值而改變的能源消耗率也將與單行程系統作比較，以探討二行程套管之加熱系統在低能源消耗率時，熱傳效率改善之最佳操作設計。 Conjugated Graetz problems by considering the heat transfer behavior in power-law fluids flowing through a double-pass concentric circular tube with uniform wall temperature are studied theoretically and solved analytically using an orthogonal expansion technique. The mathematical formulation of such a heat transfer flow problem is developed by assuming fully developed laminar velocity distribution in both inner and annular channels with ignoring axial conduction. The theoretical predictions show that the outlet temperature and Nusselt number decrease with decreasing power-law index. Comparisons between the results obtained from the concentric circular heat exchange and those of a single pass (open conduit) were presented graphically. The effect of power-law index on the heat-transfer efficiency enhancement on the double-pass device has also been discussed.
