本研究的目的為探討在非固定管壁濃度的狀態下，改變上下板壁濃度之比例對二行程平板型質量交換器的質傳之影響。本研究的二行程數學模型所推導的偏微分方程組屬於共軛格拉茲系統，利用分離變數法(separation of variables)、層疊法(superposition method)和正交展開方法(orthogonal expansion technique)，可求得通道內之濃度分佈及平均謝塢數(sherwood number)，並探討上下板壁濃度的不同比例對質傳效率提昇百分比之影響。 結果顯示，上下壁濃度的比例不同，其質傳效率也隨之改變，且隨著質傳格拉茲數的增加，平均謝塢數也會提升而導致質傳效率增加，此外，中間薄膜位置的不同及薄膜的孔隙度也會對質傳效率造成一定的影響。同時因為迴流裝置的不同所造成的預混效應、流體滯留時間及能源消耗也會有所改變。將以上條件所得結果與單行程質量交換系統相互比較，以獲得最佳操作條件與設計參數。 A new device of double-pass mass exchanger under asymmetric wall concentrations is to divide a parallel-plate channel by inserting a permeable barrier into two subchannels. The adjustment of the ratio of wall concentrations and the recycle effect was introduced to analyze the improvement of mass transfer efficiency in double-pass devices under asymmetric wall concentrations. The theoretical formulation of such conjugated Graetz problems were developed and the analytical solutions were obtained by using the separation of variables and superposition method. The theoretical predictions of the double-pass mass exchanger with external recycle were compared with those in single-pass devices under the same working dimensions. The average outlet concentration distribution and mass-transfer efficiency improvement were represented graphically with mass-transfer Graetz number and permeable membrane location as parameters. The effects of the membrane parameter and recycle ratio are also discussed in this study.
