薄膜蒸餾(Membrane Distillation, MD)是利用一多孔性疏水薄膜，在薄膜兩側提供溫度之差異，藉以因水之蒸汽壓差產生水之傳輸，達到將水純化之目的。本論文針對兩種適合應用於海水淡化之薄膜蒸餾單元進行模擬分析研究，包括直接接觸式(Direct Contact Membrane Distillation, DCMD)與氣隔式(Air Gap Membrane Distillation, AGMD)。本研究使用之模式建立於Aspen Plus®並 附加程式，探討模組內部特性分佈，包括溫度、質傳通量，以及改變操作參數與熱質傳係數對性能之影響，最後利用反應表面法建立直接接觸式與氣隔式薄膜蒸餾系統之性能模式，並探討其最佳化設計。 針對直接接觸式與氣隔式系統之分析結果顯示，影響薄膜蒸餾性能之主要條件為熱液體進口溫度、熱液體進口流量、冷液體進口流量與氣隔層壓力。在利用反應表面法建立了含熱回收設計系統之性能預測二階模式後，進行最佳化分析之結果顯示，直接接觸式應採用最低熱液體流量、最高熱液體溫度、最高冷液體流量與最小膜厚，系統效率值為8.2%；氣隔式應採用最低熱液體流量與最高熱液體溫度之設計，系統效率值為5.8%。 Membrane distillation is a separation operation employing porous hydrophobic membrane and utilizing the vapor pressure difference across the membrane due to temperature difference. This thesis investigates the application for desalination via simulation. Direct contact membrane distillation (DCMD) and air gap membrane distillation (AGMD) are studied. Simulation model is built on Aspen Plus® with a user defined unit operation written for the two types of membrane distillation, respectively. The model is different from reported in that the bulk phase mass resistances are included. Large scale modules for practical industrial applications are simulated and studied for the effects of design and operation variables, as well as the importance of heat and mass transfers of each phase. Response surface method is adopted to establish the performance-variable quadratic model and optimization is further accomplished. Analysis results indicate that the most significant variables are hot liquid inlet temperature, hot liquid inlet flow rate, cold liquid inlet flow rate and the membrane thickness or pressure of the air gap. The optimal operation should use minimum hot liquid flow rate, maximum hot liquid temperature, maximum cold liquid flow rate and minimum membrane thickness for DCMD with efficiency of 8.2% can be obtained and use minimum hot liquid flow rate and maximum hot liquid temperature for AGMD with efficiency of 5.8% can be obtained.
