本論文提出三種構造簡單，容易製作，且能產生多方向渦流以有效促進混合的微結構設計。在彎曲微流道上設置擋板，或是橢圓壁面的彎曲流道設計，都能因為離心力作用產生的橫向對流，以及流道寬度變化時所形成水平方向的擴張型渦流的共同作用，達到促進混合的目的。同時亦利用側流道注入流體的設計，使流體注入微混合器後即形成流層的三明治結構以加速混合的完成。此外，本研究也比較去離子水溶液與羧甲基纖維素水溶液在具C形蜿蜒流道微混合器中的流動與混合。
本研究以聚二甲基矽氧烷，利用光微影技術製造微混合器，並使用雷射共軛焦顯微鏡觀察溶液在微混合器中的流動與混合。同時亦以數值軟體模擬流體在微混合器中的三維流動與混合現象，並與實驗結果相比較。所得的結果顯示，本研究的數值模擬與實驗結果具有足夠的一致性。
研究的結果顯示，在彎曲流道上設置擋板能產生多方向渦流並促進混合，可觀察到下列現象: (1)將第一塊擋板連接於流道內側壁，並將第二塊擋板連接於外側壁的C形微混合器，也稱為典型C形微混合器，其混合度會優於將擋板位置設置相反的C形微混合器。(2)當雷諾數足夠大時，典型C形微混合器在第二塊擋板後側的下游處，會形成另一個分離型渦流，並更進一步地促進混合。(3)可利用直流道連接數個典型C形微混合器達更均勻的混合，在高雷諾數的流動條件尤其顯著。
為瞭解流體經由側注入流道注入的位置，對混合器內流體混合的影響，本研究比較三種具側注入流道的彎直型微混合器，包括將兩側注入流道皆設置在流體匯合處的全三層流(FTS)彎直型微混合器，將一側注入流道連接於第一與第二擋板間內側壁的(ISI)彎直型微混合器，以及將一側注入流道連接於第一與第二擋板間外側壁的(ESI)彎直型微混合器。研究的結果顯示，側注入流道的設計可使流體形成流層的三明治結構，在不需增加太多壓力輸入的操作條件下，能更有效地提升混合的效率。同時，三種具側注入流的微混合器中，全三層流(FTS)彎直型微混合器有較好的混合效率。
本研究也將蜿蜒流道的側壁面設計成兩相鄰長軸相互垂直的橢圓形壁面，使之成為具有漸縮漸擴彎曲流道的微混合器。結果顯示，當彎曲流道的曲率半徑越小且流道最寬與最窄的比值越大時，通常會有較好的混合效率，在高流率的流動條件下尤其顯著。此外，因為本設計的平順流道側壁，故僅需的較小壓力輸入即可有效地達成混合，且避免對易碎檢測樣本造成非故意的損壞。
此外，本研究也發現去離子水溶液或羧甲基纖維素水溶液在具C形蜿蜒流道微混合器中流動時，流體的雷諾數與迪恩數，會因流體的平均黏度減少而提高。因此在本研究所考慮的流動條件，去離子水因為平均黏度最低，所以流動時的雷諾數，對流的效應以及混合度都是最高的。另外，當對流效應開始能有效促進混合時，500 ppm濃度的羧甲基纖維素水溶液的平均黏度會小於100 ppm濃度的羧甲基纖維素水溶液，因此其雷諾數與混合度會高於100 ppm濃度的羧甲基纖維素水溶液。

To achieve efficient micromixing based on multidirectional vortices, we propose three simple and easily fabricated planar micromixers whose curvature is larger and channel width is varying radially. The designs are proposed to harness the Dean vortices that arise on the vertical plane of the curved channels due to the continuous action of centrifugal force and the expansion vortices that arise on the horizontal plane caused by baffles or semi-elliptical side walls. Furthermore, the designs taking the advantage of the geometric sandwiched structure of fluid streams are also adopted. Finally, we compare the flow and the mixing behaviors of the deionized (DI) water and the carboxymethyl cellulose (CMC) solutions in a C-shaped serpentine micromixer.
The micromixers are fabricated by a micro-lithography process and the mixing behaviors are observed by using a confocal spectral microscope imaging system. Numerical simulation is performed to investigate the effects of mean flow speeds, fluid properties and geometry parameters on fluids mixing. The simulation results are in reasonable agreement with the experimental results.
First, we propose the micromixers based on multidirectional vortices due to baffles and channel curvature. The concentration distributions and flow patterns obtained reveal the following trends. (i) The mixing efficiency of the C-shaped micromixer with the first baffle attached to the internal cylinder and the second attached to the external cylinder (basic C-shaped micromixer) is better than that of the C-shaped micromixer with inverted arrangement of baffles. (ii) While the Reynolds number is large enough, the basic C-shaped micromixer can generate an extra separation vortex in the downstream of the second baffle and that enhance fluid mixing future. (iii) A micromixer consisting of a few basic C-shaped micromixers connected by straight channels may generate a high degree of mixing for the case with a large Re.
Next, we compare three types of three-stream curved-straight-curved (CSC) micromixers, including the full three-stream (FTS) CSC micromixer, the CSC microchannel with internal side-wall injection (ISI) and the CSC microchannel with external side-wall injection (ESI). The present results show that the mixing efficiency increases without increasing the pressure applied much by the channel structure forming the sandwiched structure of streams. Besides, it is found that the FTS CSC micromixer is the preferable one among the three micromixers considered.
Besides, we evaluate the fluid mixing in a meandering microchannel formed by two repeated sequences of semi-elliptical side walls with the major axes of adjacent semi-elliptical side walls perpendicular to each other. The results show that the mixing efficiency of the present micromixer with a large expansion ratio defined as the width of the exit straight channel divided by the minimum width of the curved channel is generally better than that of the meander-channel micromixer with constant cross section for the case with a large flow rate and a small radius of curvature. Besides, the present micromixer has smooth side walls, and so generates less pressure drop and avoids unintentional effects on fragile speciments.
We also investigate the flow and mixing behaviors of the CMC solutions and the DI water in a C-shaped serpentine micromixer. It is well known that the Reynolds number and the Dean number increase with the decrease of the average viscosity. Since the average viscosity of the DI water is less than that of the CMC solutions in those mean flow speeds considered, the effect of the Dean vortices and the degree of mixing of the DI water are larger than that of the CMC solutions. Furthermore, while the effect of convection is significant on the fluid mixing, the Reynolds number, the effect of the Dean vortices and the degree of mixing of the 500 ppm CMC solution are large than those of the 100 ppm CMC solution, since the 500 ppm CMC solution has less average viscosity at the same mean flow speed.

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