三維交錯微管道具有許多應用可能如流體轉換、混合等，其在微流體系統中逐漸變成一重要的元件。此研究主要目的為詳細探討三維交錯管道中的流體行為並將此管道應用於微混合器中。研究中利用數值模擬、理論分析與實驗方法來確認此三維結構中的流場與混合特性。
研究顯示兩道流體在經過三維交錯處時會互相交換並轉彎到另一層管道中；我們發現一個表面積體積比的無因次參數（SV）可以有效的用來了解此一流體行為，在大部分的案例中，流體的轉彎比率會與適當範圍內的SV成線性關係。此外，我們也有系統的探討其他參數如雷諾數、擴散率、交錯角度、流速比和流阻比對流體交換比率的影響。相信經過這些參數測試後，能對相關元件中的流體控制提供一有用的參考。
接著本文研究了五種以三維交錯微管道為基準而設計的混合器，這些混合器分別在交錯與轉角處做一些改變。我們利用粒子散佈、龐加萊截面、李盼諾夫指數和混合指數來評斷各混合器中混沌的情形與混合的效能；另外也探討了雷諾數與管道深寬比對混合效能的影響。結果顯示TDCM-RU型的混合器具備了分離合併（SAR）的多層板與混沌的混合機制，展現了相當優異的混合效能，未來具有延伸應用的可能。經這些探討後，相信能對相關的三維微混合器提供一有效的設計指引。

Microchannel with three-dimensional crossing structure has a variety of applications in flow switching, mixing and so on, becoming an important component in microfluidic systems. The present study aims at understanding detailed flow behavior through this 3-D crossing of the microchannel and applying the crossing structure as a basic component to micromixer. The numerical simulation technique was chosen as the major tools for the investigation. Some theoretical analysis works and simplified experimental methods were also shown for verifying the 3-D flow and mixing characteristics.
In a 3-D crossing microchannel, the flow will turning and switching to another layer at the junction. A non-dimensional parameter of surface to volume ratio (SV) was useful to understanding the flow behavior. The results showed that in a moderate range, the turning fraction is proportional to the SV for most cases. In addition, the effect of various parameters such as Reynolds number, diffusivity, crossing angle, flow rate ratio and flow resistance on the fraction of flow turning are also systematic investigated. From the comprehensive investigate of these parameters, it is expected to provide useful guidelines for the control of flow in microfluidic devices among others.
Based on the flow features of 3-D crossing microchannel, the mixing can be achieved by an appropriate design. Five different micromixers which have various crossing or bending patterns was designed and investigated. The chaotic behavior and mixing efficiency were identified using four different methods (particle dispersion, Poincar sections, Lyapunov exponent and mixing index) for qualitative and quantitative estimation. The influence of Reynolds number and aspect ratio are also studied. All of the results showed that the new design of TDCM-RU (which combines two mixing mechanisms of split-and-recombine and chaotic advection) has the best mixing efficiency among other designs. The mixing index can achieve to 0.78 after four crossing times at low Reynolds number, while the Xia-B can only to 0.33. Even in high Re, TDCM-RU also reveals an excellent mixing just by adjusting the aspect ratio of channel. The results provide useful design guidelines for 3-D micromixers. Also, the TDCM-RU has a great potential for practical use in chemistry, biochemistry and combustion.

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