摘要
混合在微流系統中為一重要課題。本論文中藉由數值模擬與實驗方法研究電熱力微混合器。此混合器基本上為一Y型微流道，在其主流道底壁上建置有經過設計的電極作為混合的驅動源。若將兩長條狀電極 (寬度100μm)末端平行相對 (間距30μm)，當施加相位差180度的交流電壓時，我們發現在電極角落上方電解質內共形成四個漩渦。漩渦為三維且兩相鄰漩渦作相反方向旋轉。我們在流道底部以鋸齒狀分佈建置多組上述電極對。由理論研究得知，漩渦乃由電熱力作用所產生；我們將利用此等漩渦對兩股注入Y型流道的流體作主動式混合。我們利用COMSOL軟體作數值分析及以實驗配以PIV量測技術，研究漩渦的流動結構。就懸浮於流場中的微米等級粒子運動，其實驗和計算結果在定性和定量上皆相符合。我們對操作電壓(8Vpp-12Vpp)和流體導電率(0.1-1 S/m)作了參數分析。渦流強度隨著電壓和導電率的增加而增加。模擬中亦進行改變電極末端形狀的計算，結果顯示矩形電極較其他種形狀的電極更能產生較強的漩渦。 在混合效能的實驗中，我們由Y型流道的兩個入口分別注入含有螢光染料及深藍色染料的混合液，入口流道300μm高30μm，兩股流體滙流進寬400μm高30μm的主流道進行混合，其總流量為0.5μl/min(平均速度694μm/s，雷諾數0.039)。實驗結果顯示混合指標和操作電極及流體導電率成正比，且操作電壓的影響更為顯著。混合效應在流體導電率1S/m且操作電壓12V時達到81%。
並列摘要
Mixing is an important topic in micro-fluidic systems. We studied here an electro-thermal micro mixer via both theoretical simulation and experiment. The mixer is essentially a Y-type micro channel with designed electrodes built on the bottom wall of the straight main channel. When two striped electrodes (with width 100μm here) are placed with their ends closed to each other (30μm spacing in the present study), we observed four vortices in the electrolyte above the four corners of the electrodes when they are powered by ac voltages with 180 degree phase difference. The vortices are flat but three dimensional and their senses are counter rotating for any two neighboring vortices. Many pairs of such electrodes are built as arrays and arranged in a saw-tooth manner on the bottom wall of the channel. Those vortices are electro-thermal in origin according to a theoretical study, and were employed to perform active mixing of two different fluid streams entering the Y-type channel. The flow structure was studied quantitatively via numerical calculation with the aid of the COMSOL software, and via experiment using PIV technique. The general feature of the flow according to the image of the motion of the suspended particles agrees qualitatively and fairly quantitatively with the calculation. In particular, we compared the fluid velocity on the vertical mid plane of the electrode gap region obtained from both calculation and PIV measurement. Effects of applied voltages (from 8 to 12 volts peak-to-peak) and electrolyte conductivity (from 0.1 to 1 S/m) were also studied. The strength of the vortices increases rapidly with the applied voltage and electrolyte conductivity. Different electrode shapes were also studied numerically, and it was found that the rectangular shape is more favorable for generating stronger vortices. Mixing experiment were carried out using solutions with fluorescent and dark blue dye feeding separately into the two inlets (with width 300 μm, height 30 μm, flow rate 0.25 μl/min) of the Y-channel. Mixing occurs above the electrode region of the main channel with 400μm in width and 30μm in height at a total flow rate 0.5μl/min (averaged speed is 694μm/s, Reynolds number is 0.039). The mixing indexes increase with the applied voltage and the electrolyte conductivity, and the voltage effect is more significant. Mixing index reaches 81% under 12V for an electrolyte with conductivity 1 S/m.