Analysis on hydrodynamics and cake formation of dynamic microfiltration with different rotating-disk designs

淡江大學機構典藏 > 工學院 > 化學工程與材料工程學系暨研究所 > 學位論文 > Item 987654321/114656

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题名:	Analysis on hydrodynamics and cake formation of dynamic microfiltration with different rotating-disk designs
其它题名:	設計不同迴轉盤在動態微過濾中流體力學與濾餅形成之解析
作者:	吳思恩;Wu, Su-En
贡献者:	淡江大學化學工程與材料工程學系博士班鄭東文;Cheng, Tung-Wen
关键词:	微過濾;迴轉盤動態過濾器;計算流體力學;幾何結構設計;海水淡化前處理;微藻濃縮;microfiltration;Rotating-disk dynamic filter;computational fluid dynamics;Structure design;Seawater pretreatment;Microalgae concentration
日期:	2017
上传时间:	2018-08-03 14:59:45 (UTC+8)
摘要:	本研究設計不同迴轉盤並解析在動態微過濾中之流體力學與濾餅形成。微過濾應用中薄膜結垢被視為主要缺點，為了提高過濾性能和降低功耗，在動態過濾中使用迴轉盤所產生之剪切力可減少薄膜結垢。本研究的第一部分是評估局部過濾通量和濾餅之不均勻性。為了瞭解轉速對過濾性能和通量行為之影響，可藉由過濾實驗中分析濾餅形成機制、局部濾餅特性和粒徑分佈。此實驗部分是使用平均孔徑為0.1 μm之醋酸纖維酯膜過濾粒徑分佈為1.5 μm至25 μm之聚甲基丙烯酸甲酯（PMMA）球型微粒，並且使用計算流體動學（CFD）模擬薄膜表面上的速度和剪切力分佈，藉由力平衡方程式結合實驗局部濾餅性質可分析濾餅形成機制。局部過濾通量、臨界粒徑和操作條件之間的關係可推導出非線性方程式。此研究方法可以估計局部濾餅量和過濾通量，找出最佳操作條件，作為設計高效迴轉盤結構或過濾模組支之基礎。本研究的第二部分是在動態微過濾中選擇最佳操作條件與迴轉盤幾何結構以去除海水中之膠體結垢物。此研究使用計算流體力學模擬各種類型的迴轉盤在動態過濾器中的流體流動。藉由剪切力模擬值可建立濾餅質量和過濾通量之經驗方程式，並且基於過濾性能和功耗之間的關係設計出最佳迴轉盤幾何結構。由結果指出，除去海水中微粒可操作於低轉速度且具有兩個圓形通孔葉片的迴轉盤有高過濾通量和相對低的功率消耗。本研究的第三部分為在動態過濾系統中設計九種迴轉盤並評估微藻濃縮和薄膜結構之過濾性能。藉由過去研究所得知的微藻濾餅性質，並選擇適當的模型以估計濾餅質量和過濾通量。從平均薄膜表面剪切力估算可建立濾餅質量和過濾通量的關係經驗式，並且以高過濾通量和低功耗之間的觀點來判定迴轉盤之最佳設計，本研究可提供未來設計迴轉盤動態過濾器和最佳化操作的指引。 This thesis investigated the hydrodynamics and cake formation with different rotating-disk designs in dynamic microfiltration. Membrane fouling is recognized as a major drawback for the application of microfiltration. In order to enhance high filtration performance and low power consumption, the reduction of membrane fouling, which is caused by the shear stress at the membrane, is created by a rotating-disk in dynamic filtration. A local flux behavior and cake properties was evaluated to represent the nonuniformity of cake formation. In order to understand the effect of rotating speed on filtration performance and flux behavior, mechanism of cake formation, local cake properties, and particle size distribution were investigated in the filtration experiment. The mixed cellulose ester membrane with mean pore size of 0.1 μm was used for filtering Polymethyl methacrylate (PMMA) spherical fine particles with the particle size distribution ranged from 1.5 μm to 25 μm. The distributions of velocity and shear stress on the membrane surface were simulated using computational fluid dynamics (CFD). Combined with experimental data concerning local cake properties, the mechanism of cake formation based on a force balance model was analyzed. The relationship between local filtration flux, critical particle size, and operation conditions can be expressed as a nonlinear equation. This method estimates the local cake mass and filtration rate for optimizing operating conditions and designing high-efficiency disk structures or filter modules. The selection of optimum operating conditions and the design of disk structures for removing colloidal foulants from artificial seawater was applied in rotating-disk dynamic microfiltration. The fluid flows in dynamic filer with various types of rotating disks were simulated using computational fluid dynamics. The cake mass and filtration flux were estimated from the shear stress and calculated using empirical equations. The optimal design of rotating-disk was determined from comparing the filtration performances and power consumptions. The results indicated that a rotating-disk with two vanes of circular orifice under low disk rotation speed shows the optimal design and operating condition in removing the particles from seawater with high filtration flux and relatively low power consumption. Nine types of rotating-disk were designed and installed above the filter membrane in a filter chamber to study the filtration performances of microalgae concentration and membrane fouling. The cake property of microalgae was obtained from our previous study, and proper models were chosen to elucidate the cake mass and filtration flux. Once the mean shear stress on the membrane surface was known, the cake mass and filtration flux were estimated based on empirical equations. The optimal design of the rotating-disk was then determined from the viewpoints of high filtration flux and low power consumption. This study provides a guide for the design and optimized operation of rotating-disk dynamic filter.
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