薄膜蒸餾是以疏水性微孔膜做為分離膜，膜兩側分別為熱流之進料水溶液及促使水蒸氣凝結之冷流，利用熱流與冷流間之溫度差為驅動力，經由疏水性微孔，水蒸氣從熱流側傳送至冷流側，因此只需加熱進料溶液(海水)便可藉由薄膜蒸餾製造出純水。以薄膜蒸餾進行海水淡化時，除了因海水中多種雜質成分及高濃度鹽分引發之結垢問題，還有因溫度差驅動力引起之濃度極化與溫度極化等效應，濃度極化會使水溶液蒸氣壓降低，溫度極化會抵銷部份之驅動力，因此降低薄膜模組內薄膜結垢與極化等問題，可提升薄膜蒸餾之操作效能，有助於海水淡化薄膜蒸餾系統的開發及應用。真空式薄膜蒸餾應用於海水淡化具有高通量之優勢，但濾液側需抽真空，耗費較多電能。本整合計畫中子計畫一為太陽熱能產電之研究，子計畫二為太陽熱儲熱之研究，在電能及熱能供應無慮下，並配合優良之薄膜模組設計，將使真空式薄膜蒸餾更具有競爭性。本子計畫將對真空式薄膜蒸餾模組之最佳化設計進行探討，第一年進行平板型模組真空式薄膜蒸餾，討論通道型式改變及流動流態等對蒸餾通量提升之影響，並與前期計畫之直接接觸式薄膜蒸餾做一綜合性比較；第二年則以第一年成果為基礎，進行改良型卷式(spiral-wound)模組之研究，討論支撐層、流動方式、及氣-液操作等對真空式薄膜蒸餾通量促進之影響；第三年進行改良型卷式模組與中空纖維模組性能之比較，探討在不同操作變數下蒸餾通量之行為表現。本研究計畫之成果，可做為子計畫四及子計畫五系統化設計之依據，使薄膜蒸餾海水淡化系統更具有競爭性及經濟效益。 Membrane distillation (MD) is a thermally-driven separation process in which a hydrophobic micro-porous membrane separates a hot feed stream and a cold permeate stream. This process can be applied in seawater desalination while circulating the hot seawater through the membrane module and collecting the desalination water at the cold side. However, in addition to the membrane fouling caused by the salts and impurities in seawater, both the phenomena of concentration polarization and temperature polarization affect the performance the MD process. Research on the methods in reducing the effects of those phenomena is essential and benefit to the application of membrane distillation in seawater desalination. Vacuum membrane distillation (VMD) is the one of the MD processes that has the advantage of high distillate flux, but high electric energy is consumed for vacuuming. In present group proposal, electricity production by concentrated solar powered Stirling engine will be investigated in sub-proposal 1, and solar thermal heat storage is studied in sub-proposal 2. Therefore, an efficient VMD membrane module with fully supply of electricity and heat will become more powerful in seawater desalination. This sub-proposal aims to the research and development of optimal membrane module design for membrane distillation. In first year, the study focuses on the optimal module channel design and fluid flow pattern in the flat-plate VMD module, and performance comparison between VMD and DCMD; In second year, the results of year one will be applied to the development of modified spiral-wound module with consideration of spacer design, flow type or gas-liquid two-phase flow in distillate flux enhancement. And, in third year, the performance comparison between the modified spiral-wound module and the commercial hollow-fiber module will be studied under various operating parameters. The outcome of this proposal can provide the basic information for economic systematical MD design by sub-proposals 4 and 5.