本研究針對於質傳問題發生在固定質量通量且具有迴流效應之平板型質量交換器的共軛格拉茲系統，並建立數學模型及求得其解析解。此系統以分離變數法(separation of variables)及重疊理論(superposition method)，且利用正交展開法(orthogonal expansion technique)，求其濃度分佈及平均謝塢數(Sherwood number)，同時亦探討迴流效應對平板式質量交換器之質傳效率的影響，並將其質量傳送效率之改善與單行程系統作比較。 在本文中，主要探討設計參數(即迴流型式、薄膜位置及薄膜穿透度)與操作參數(即迴流量及體積流速)對平板型質量交換器之影響。結果顯示，本系統在質傳格拉茲數較大時，管壁上的濃度降低及兩端濃度變化量較小，將有利於材料的選擇，而不同的薄膜位置及薄膜的穿透率亦對質傳效率有顯著影響。再者，對不同迴流型式與迴流比值在不同薄膜位置的能源消耗也將與單行程系統作一番比較，以探討平板型質量交換器之最佳設計與操作條件。 A new device of the double-pass mass exchanger is to divide a parallel flat-plate channel by inserting a permeable barrier into two subchannels with external refluxes under uniform wall mass fluxes. The resultant mathematical formulation of such a double-pass device, referred to conjugated Graetz problems, was developed theoretically. The analytical solution was obtained by using the superposition principle and an orthogonal expansion technique in power series. The concentration distribution and mass transfer efficiency were represented graphically, and compared with those in single-pass devices (without a permeable barrier inserted) of the same working dimension. The results show that the concentration gradient on the wall can be significantly reducing by introducing recycle operations for double-pass mass-exchangers. The effects of permeable-barrier position and recycle ratio on the mass transfer efficiency as well as on the increment of power consumption have also been discussed.
