使用計算流體力學設計新型迴轉盤以提升微過濾之分離效率

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 987654321/94361

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题名:	使用計算流體力學設計新型迴轉盤以提升微過濾之分離效率
其它题名:	Novel design of rotating disk for improving separation efficiency of microfiltration by CFD
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碩士班黃國楨
关键词:	微過濾;迴轉盤;過濾;計算流體力學;microfiltration;Rotating disk filter;Filtration;CFD
日期:	2013
上传时间:	2014-01-23 14:27:39 (UTC+8)
摘要:	本研究使用計算流體力學(CFD)的方法來討論迴轉盤結構對速度和剪應力分佈的影響，其中結構的改變包含了迴轉盤葉片的種類與數目。研究選用的模組為內置迴轉盤的單一圓柱形濾室，並且將濾膜固定在靠近濾室底部的多孔性支撐材。本研究利用Fluent計算流體力學軟體來模擬三個維度之模組內部流場，其數值方法為網格有限體積法與紊流中的RNG k-epsilon模式進行連續及動量守恆方程式求解，並且選用不同迴轉盤結構與改變操作條件進行分析探討。迴轉盤的操作轉速設定至3000 rpm並且選用進料流速範圍從1.18 m/s到3.18 m/s。在不同操作條件下之速度、壓力和剪應力的模擬結果與先前文獻和實驗數據相比較。由結果可以得知，迴轉盤的轉速是主導過濾通量的最重要因素，在無葉片迴轉盤系統轉速每增加1000 rpm，提升幅度約20至30 %。最適化的葉片設計可以有效地提升濾膜表面的剪切力，達到更高的過濾通量與更低的薄膜結垢，以加裝雙凹凸狀之迴轉盤效果最佳。另外，在固定的系統轉速下，迴轉盤上的葉片越多會造成濾膜表面上的剪應力更高，每多增加一個葉片會使得剪切力提升約30 Pa。然而，增加葉片的數目亦會導致越大的耗能，造成越高的操作成本；隨著葉片數目的增加會使功率急遽地的提升，但濾速的上升卻是趨緩的情況，四個葉片功率3290 J/s。 Rotating-disk filtration modules have been increasingly used for solid-liquid separation in industrial processes in recent years. The high shear stress generated by rotating disk is believed to effectively reduce the cake formation and concentration polarization on the membrane surface, as a result, to enhance the filtration flux. To evaluate the shear stress and the velocity distributions are therefore the essential steps not only to grasp the filtration performance but also to design high-efficiency modules. In this study, the effects of rotating disk structure, including the blade type and number, on the velocity and shear stress distributions are discussed using computational fluid dynamics (CFD). The module consists of a testing rotating disk installing inside a cylindrical chamber. A circular membrane is fixed on a porous support near the chamber bottom. The 3-dimensional flow fields in the module with different rotating disks under various operating conditions are simulated using the Fluent CFD software. The equations of continuity and momentum balances are solved numerically using a finite volume scheme with the Renormalization-Group k-epsilon model. The disk rotating speeds are set up to 3000 rpm, and the inlet suspension velocity ranges from 1.18 to 3.18 m/s. The simulated results of velocity, pressure and shear stress profiles under various conditions are compared with those in previous study and experimental data. It can be concluded that the disk rotating speed is the most important factor in determining the filtration flux. The optimum disk design for higher permeate fluxes and less membrane fouling can be achieved by increasing the shear stress on the membrane surface. A disk with more blades could generate higher shear stress on the membrane surface under a given rotation speed. However, more power should be supplied to drive the rotating shaft and disk.
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