薄膜蒸餾為海水淡化技術之一，用來製造純水提供民生及工業使用。其特色為占據體積小、可操作在常壓、低溫熱源與可模組化等優點。本研究主要針對在薄膜蒸餾系統中，薄膜係數為預測理論純水透膜通量之重要參數。因此本研究將以攪拌型直接接觸式薄膜蒸餾系統，藉由改變不同操作條件，求得薄膜兩側膜面溫度，再利用最小平方法建立一薄膜係數經驗公式。進而建立雙效型直接接觸式薄膜蒸餾系統之二維數學模型，對其質量與熱量傳送機制進行研究，並將薄膜係數經驗公式代入，以實驗分析輔以驗證數學模型之正確性。本研究求解是先利用有限差分法將偏微分方程式簡化，再使用四階Runge-Kutta數值方法求解，得到通道內溫度分佈及理論純水透膜通量。研究結果顯示雙效型直接接觸式薄膜蒸餾系統實驗值與理論值平均相對誤差(1)純水：3.97%；(2)鹽水：5.46%。結果顯示，純水透膜通量會因提升攪拌轉速、提升熱側進口流體溫度與提升體積流率而增加。溫度極化係數隨著攪拌轉速的提升與進口體積流率增加而趨近於1。 The direct contact membrane distillation(DCMD) device is a simple design of MD systems in which both the cold stream and hot stream are kept in direct contact with the membrane. The advantages of DCMD lie in its simple configuration, the need for only small temperature differences and nearly 100% salt rejection. In this study, the DCMC process are performed at middle temperature operation (about 40 °C to 70 °C) of hot inlet stream associated with a constant cold stream inlet temperature(about 25 °C). A concurrent flat-plate device was constructed and carried out to verify the theoretical prediction of pure water productivity on saline water desalination. The purposes of this study are (1) to develop a new semi-empirical expression of the membrane coefficient from the results of the pure water production of the experiment and the mathematical modeling; (2) to study a new design of double-effect direct contact membrane distillation system and develop a two-dimensional mathematical model and propose a general numerical method for solving this complex mathematical model in predicting pure water productivity in membrane distillation systems. The numerical results from the mathematical modeling of the resultant partial differential equations were obtained using the finite difference technique of the fourth-order Runge-Kutta method. The influences of the inlet saline water temperature and volumetric flow rate on the pure water productivity as well as the hydraulic dissipated energy are also delineated.
