本研究是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。本研究乃是於平板中平行加裝一可忽略厚度熱阻之隔板並加入迴流裝置，此熱傳系統是屬於共軛格拉茲問題，利用分離變數法(separation of variables)、層疊定理(superposition method)和正交展開法(orthogonal expansion technique)，求其溫度分佈及納塞數，並探討上下板溫度比例、格拉茲數與隔板位置對二行程平板型熱交換器熱傳效率之影響。 結果顯示，本系統上下板溫度比例、中間隔板位置與格拉茲數改變時，皆會對熱傳效率及平均納塞數產生影響。熱傳效率主要是受到預混效應與滯留時間這兩種效應相互影響，因不同的隔板位置，格拉茲數與迴流比之大小，皆會影響流體在通道內的滯留時間，並且非對稱系統中上板溫度較高，以上操作條件之迴流方式與上通道滯留時間對熱傳效率有相當的影響，將結果與單行程熱交換系統作比較，藉此找出非對稱固定壁溫度二行程平板式熱交換器之最佳操作設計。 The study on the new device of double-pass parallel-plate heat exchangers under asymmetric wall temperatures which adjusting the ratio of top and bottom wall temperatures has been developed theoretically, the recycle effect is also the important issue. The analytical solutions to the resultant mathematical formulations for such conjugated Graetz problems were achieved by using the separation of variables, superposition principle and an orthogonal expansion technique in extended power series. The results of heat transfer efficiency are represented graphically and compared with those in single-pass devices of the same working dimension. Analytical predictions show that adjusting the ratio of top and bottom wall temperatures, recycle effect and residence-time can affect the heat transfer efficiency in designing double-pass parallel-plate heat exchangers under asymmetric wall temperatures.
