薄膜模組間隔網內輸送 機制之微觀流力解析

Microhydrodynamic Analyses of Transport Phenomena in Spacer-filled Membrane Module

李雨霖(Yu-Ling Li)

指導教授 ： 童國倫

中原大學/工學院/化學工程研究所/博士(2007年)

https://doi.org/10.6840/cycu200600889

摘要

本研究以計算流力、影像拍攝法、壓降和透過量之實驗量測法，進行薄膜模組間隔網（spacer）內輸送機制之微觀流力解析。過去文獻對膜組間隔網進行理論與實驗分析時，皆以平板系統流來進行理論分析，而真實螺捲式膜組（spiral-wound module）內的渠道是具有彎曲度的，因此理論預測結果常與實驗值具有相當程度的差異。
本文內容針對不同薄膜模組渠道之彎曲度、膜組間隔網之類型、膜組間隔網纖維直徑之大小排列、薄膜透過率和掃流速度探討對內置間隔網膜組渠道之壓降、剪應力和粒子沉積之影響。結果顯示當膜組渠道彎曲度增加時，內外膜層剪應力和透過量之差異值將隨之增加，進而造成螺捲式膜組內外膜層不同之剪應力與透過量；而這種現象將會導致螺捲式膜組渠道內外膜層產生不同的堵塞特性，進而對整個膜組的分離效能造成影響，因此，本研究透過理論與實驗分析，提出調整纖維直徑大小的方法來改善：內外層剪應力分佈不均、透過量和粒子沉積率（deposition ratios）不同，並獲得最適化之設計參數。
此外，就二維簡化系統的階梯型膜組間隔網渠道而言，流體通過壁面上的膜組間隔網纖維時，會在纖維前後形成迴流區；但是在不同位置下所產生的迴流區，卻有不同的效應：纖維後方之迴流區是會把粒子帶走，但是纖維前方的迴流區卻會把粒子帶入膜面沉積。
另外，從三維系統的鑽石型膜組間隔網渠道研究發現：粗直徑的膜組間隔網纖維可增加其對面膜面區域之剪應力和透過量，卻造成纖維與膜面之間的渠道縮小，導致粒子在通過纖維與膜面時，受到垂直膜面之拖曳力增加，而沉積於膜面上；而從剪應力分佈結果是無法完全說明粒子之沉積行為，還需藉由流場分佈才可以解釋其粒子之沉積機制。
最後，基於以上多相流之計算流力研究及實驗技術，本研究建立了一基礎的膜組間隔網渠道之研究平台，並提供了有助於了解其他薄膜模組設計之方法。

關鍵字

螺捲式膜組 ； 膜組設計 ； 彎曲度 ； 計算流力 ； 間隔網

並列摘要

Effect of spacer design on fluid flow and separation efficiency in a spacer-filled channel was conducted using computational fluid dynamic (CFD) and experimental techniques. The spacer serves both as mechanical stabilizer for channel geometry and turbulence promoters for reducing polarization phenomena near the membrane surface. Previously, several factors affect the pressure drop and mass transfer in a spacer-filled spiral-wound module have been studied based upon flat channel module. However, the curvature of the spacer varies along the spiral flow path. No any effort has been placed on the effects of curvature of the spacer in the spiral-wound modules on the pressure drop, shear stress and filtrate rate through the curved module.
Purposes of this study were emphasized on the effects of curvature of the spacer-filled channel, filament arrangement, feed velocity and membrane resistance in the spiral-wound modules on the pressure drop, shear stress and particles deposition through the modules by CFD, experimental equipment and direct observation through the membrane. Results showed that increase of the curvature of the spacer-filled channel will result in increases the shear stress ratio and variations in inner and outer filtrate. On the other hand, the spacer-filled curved channel in a spiral wound module causes unequal shear stress at inner and outer membrane surfaces. Such unequal shear stress at the inner and outer surfaces would be expected to have an adverse impact on the membrane module performance because of different fouling characteristics for adjacent membrane leaves. Results showed that decreasing of the diameter of outer filament and increasing of the diameter of inner filament can improve this adverse impact.
Furthermore, particle deposition in spacer-filled membrane modules is investigated using a computational fluid dynamic (CFD) technique. The flow field and particle transport in the channels with permeable membrane surfaces are calculated using the commercial available CFD software FLUENT®. A scheme similar to the Eulerian–Lagrangian numerical method is adopted for the two-phase flow simulation. Particle transport in spacer-filled channel is analyzed by considering fluid drag, body force, lift force and interaction forces exerted on the colloids. Feed velocity, permeation flux, and spacer arrangement effects on particle deposition are discussed comprehensively. Based on conclusive preliminary study results, multi-phase flow simulation can provide microscopic understanding of the fouling mechanism in the spacer-filled channel and prove to be a powerful tool to aid in membrane module design.
Finally, a platform was constructed based on multi-phase CFD approach and experimental techniques for fundamental study of membrane module design.

並列關鍵字

spacer ； curvature ； spiral-wound module ； computational fluid dynamics (CFD)

參考文獻

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