本研究使用冪次流體為工作流體，探討一個具迴流之非對稱固定壁溫度二行程平板式熱交換器，改變其上下板溫度比例、格拉茲數與隔板位置以獲得最有效率之熱傳效果。此熱傳系統之統制方程式屬於共軛格拉茲問題 (conjugated Graetz problem)，本研究應用分離變數法、重疊原理 (superposition)及正交展開法(orthogonal expansion technique)求其解析解，求得於壁固定溫度比例下，兩平板間流體的溫度分佈與平均納塞數 (average Nusselt number)。此外，亦探討改變冪次定律指數、不同壁溫度比例、迴流比值、隔板位置和迴流型式等參數下的熱傳現象之改善效率，並與單行程熱交換器作比較。結果顯示，本研究之實驗數據與理論模擬結果趨勢相符合，且可發現預混效應與滯留時間為影響熱傳效率之主要因素，並可發現冪次指數愈小的流體所獲得出口溫度較低。 The conjugated Graetz problem of a double-pass parallel-plate heat exchanger under asymmetric wall temperatures improvement is investigated theoretically and experimentally to enhance the device performace improvement. The theoretical mathematical model is solved analytically using the separation of variables, superposition principle and an orthogonal expansion technique in extended power series. The analytical predictions show that the power-law fluids in such a double-pass operation results in the significant heat-transfer efficiency improvement as compared with those in an open conduit (without an impermeable resistless sheet inserted), especially when the double-pass device was operated in a larger Graetz number. The results show that the good agreement between the experimental results and theoretical prediction is obtained. The effects of the ratio of top and bottom wall temperatures, impermeable-sheet position, recycle ratio and power consumption increment for power-law fluids have also been presented.
