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標題: 比較流體聚焦與T型微流道生成乳化液滴之數值模擬
Numerical investigation of droplet emulsion in flow-focusing and T-junction microfluidic devices
作者: 劉建伯
Liu, Chien-Po
關鍵字: flow-focusing;流體聚焦;T-junction;microfluidic emulsion;surface energy;pressure work;kinetic energy;VOF;T型;微流體乳化;表面能;壓力功;動能;VOF
出版社: 機械工程學系所
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利用微流道生成微奈米乳化液滴與液滴內快速混合的應用中,流體聚焦與 T 型是經常使用的微流道結構。但是,鮮少有人比較兩流道對微流體乳化現象,以及液滴生成過程中消散相混合現象的差異。本研究利用三維有限體積數值法,搭配 VOF 模組,分別模擬流體聚焦與 T 型微流道生成乳化液滴現象,並導入物質傳遞方程式,比較兩流道對於液滴內混合現象的影響。藉由消散相流體的表面能、壓力功、動能,以及流體界面的變化,分析液滴生成的過程包括成長、拉伸、斷裂與縮回等四階段。成長期消散相排開連續相進入流道,表面能緩緩上升,動能降至最小值;拉伸期流體界面大幅度的彎曲變形,並往下游流道拉伸,表面能與動能迅速上升,壓力功降至極小值;斷裂期消散相斷裂生成液滴,能量變化達最大值;縮回期消散相往上游縮回,表面能與動能往下降,並開始下一次成長期。模擬結果發現在 Squeezing 與 Dripping 型態,流體聚焦比 T 型流道生成的液滴直徑約小 6%,在 Jetting 型態則是約小 19%。除了 Jetting 之外,其他生成型態顯示流體聚焦比 T 型流道的壓力功變化幅度約大 26%。並發現兩流道的消散相動能上升過程非常相近,但是在斷裂期與縮回期,流體聚焦的動能起伏明顯比T型的劇烈。關於液滴內混合現象的差別,雖然流體聚焦的消散相生成一對明顯的渦漩,T 型則呈現單一個明顯的渦漩。但是,流體聚焦生成的液滴的混合效率比 T 型約小 64%,顯示渦漩對 T 型流道的液滴內混合的助益遠大於流體聚焦流道。

In this investigation, the three-dimensional finite volume method (FVM) along with the volume of fluid (VOF) model was employed to simulate droplet formation in flow-focusing and T-junction microfluidics. Oil was taken as the continuous phase fluid and glycerol solution as the dispersed fluid to form water-in-oil droplets. In addition, the species equation was solved for comparison of binary mixing within the droplets generated during the emulsion process for both the flow-focusing and T-junction microfluidics. The mechanism of droplet emulsion is analyzed in terms of variations of energy for the dispersed phase fluid. It is found that the emulsion process can generally be divided into four stages, namely growth, elongation, break-up and shrinkage, according to the variations of kinetic energy, surface energy and pressure work computed for an entire period of forming an individual droplet. Moreover, the images of droplet formation in different types, including squeezing, dripping and jetting, were discussed with the energy variations. It is also found that droplets formed in a T-junction device are larger in size than that in a flow-focusing device, especially in the jetting regime. The simulations for two fluids mixed within the droplets show that the mixing efficiency for those formed in the T-junction always exceeds in the flow-focusing. This is mainly due to the fact that a pair of symmetric vortices developed within the droplets of dispersed phase fluids in the flow-focusing device while only one in the T-junction device that largely helps the advection of the fluids to be mixed.
其他識別: U0005-0911201016324900
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