表面親疏水性與毛細效應對Y 字型微流道中流體流動與包覆氣泡現象影響之研究

Abstract

本研究針對一Y 字型微流道之流體流動，透過數值模擬與實驗觀察來探討流體慣性力、表面張力、流道壁面附著力與流道幾何參數對流體流動與流體新月形波前包覆氣泡現象之影響。我們利用微機電系統之概念和製程技術，設計出幾何參數不同的Y 字型微流道裝置，藉由觀測及分析液體於不同流動條件下，在精心設計之流道內流動之現象。 為了歸納出流體新月形波前包覆氣泡現象之主要影響因素，本研究我們選取的參數有：入口流體流量、流道壁面親疏水性、流道深寬比與流道夾角。數值模擬部分我們採用商業化計算流體力學軟體CFD-ACE+來進行；透過邊界條件給予液固接觸角以模擬不同親疏水性，再利用流體體積-片段線性界面重建法來做液氣界面的時變追蹤，並以連續表面力法來考慮表面張力的效應。 研究結果顯示，主要影響氣泡包覆現象之參數為夾角及接觸角。其夾角越大越會產生氣泡包覆，且體積越大。接觸角越大越容易產生氣泡包覆，氣泡體積也越大。深寬比越大造成波前之法線夾角的改變與速度加快，使親水性案例氣泡體積增加。速度快會造成波前之動態接觸角稍微增加，使親水性案例氣泡體積增加。降低速度可以使波前快速達到穩態，並且消除壁面角落因速度太快而造成的小氣泡。

This research purposes to study the physical phenomenon and fluid dynamics of microfluid having encapsulated air bubbles at advancing meniscus in the microchannel with Y type. The varying physical parameters include inlet mass flow rate, wetting conditions of microchannel walls, aspect ratio of microchannels, and angle formed by microchannels. The numerical simulation tool used in this study is the CFD-ACE+ commercial software produced by CFD Research Corporation. A VOF-PLIC interface tracking method is adapted to represent the fluid domain and to track the evolution of its free boundaries while CSF mode is choosed to model interfacial physics. According to the research result, the main parameters that affect the formation of encapsulated air bubble include inlet angle of micro-channels and wetting condation. The increase in the inlet angle will produce encapsulated air bubble with lager volume. The lager contact angle will easily come out with encapsulated air bubble with having lager volume. The lager aspect ratio will result in the change angle of meniscus normal line, faster the speed, and increase volume of air bubble for hydrophilic cases. Faster speed will step up dynamic wetting angle of meniscus slightly and volume of air bubble for hydrophilic cases. lower speed can make meniscus attain to steady state and eliminate the small air bubble on wall corner due to fast speed.