本研究是設計加裝一可忽略熱阻之隔板於圓形管中，使之成為一組外管壁熱通量為正弦函數且具有迴流裝置之套管型熱交換器，其工作流體為冪次流體，此熱傳系統之統制方程式屬於共軛格拉茲問題(conjugated Graetz problem)，本研究以近似解(approximation method)並利用弗賓納斯法(Frobenius method)來求解，可求得管內溫度分佈及納塞數(Nusselt number)。此外，亦探討改變冪次指數、不同隔板位置、迴流比值和迴流型式等參數下的熱傳效率，且與單行程無隔板系統作比較。結果顯示，加裝回流裝置後之熱交換器，其效率提昇率有明顯改善，而不同的隔板位置對系統之間的效率亦有顯著影響。同時在本文中，迴流系統因隔板裝置及不同的迴流比值而增加的能源消耗率也將與單行程系統作比較，藉此達到熱傳效率改善之目的。 A new design of heating the power-law fluid with sinusoidal wall fluxes was obtained inserting in parallel an impermeable sheet into a concentric tube to conduct double-pass operations. The mathematical formulation of counterflow double-pass concentric-tube heat exchanger under sinusoidal wall fluxes, as referred to conjugated Graetz problem was achieved by using the Frobenius method. The theoretical predictions show that the improvement of the double-pass device performance with the significant heat-transfer efficiency improvement was represented graphically, and heat transfer enhancement of double-pass concentric circular heat exchangers is generally higher than that in the single-pass operations (without an impermeable sheet inserted). The results show that introducing recycle operation can enhance the heat-transfer efficiency in designing double-pass concentric-tube heat exchangers with sinusoidal wall heat fluxes. The effects of power index, impermeable-sheet position, recycle ratio and power consumption increment for heating power-law fluids in the double-pass concentric tube heat exchanger have also been presented.
