本論文主要在於研究微流體混合器。分別使用被動式與主動式混合方案以改善微流體混合器的混合效率。主要的研究重點共分為三項：
首先，在被動式混合方案的研究上，分析電驅動流在不同波形表面結構的流道內之混合特性。在這個混合技巧中，因為波形表面的影響，使流體能沿著彎曲狀的流動路徑通過流道，藉此可增加界面接觸面積，並改善混合效率。模擬結果顯示，增加流道內波形表面的振幅或波形表面區段之長度均能改進混合效率。此外，藉由在波形表面上使用異質性的表面電荷，可進一步地加強混合效率。分析結果指示，在異質性表面附近能產生局部的迴流現象，並能顯著地提高混合效率。
其次，在主動式混合方案的研究上，分析電驅動流受混沌（chaotic）電場作用下，流道內的流體流動特性及其混合效果。在這個混合方法中，使用杜芬（Duffing）系統取得混沌的振盪電位，並將此混沌的振盪電位應用到混合室壁面的四個電極上，以擾動流體。分析結果顯示，在混沌振盪電位的作用下，能在混合室內產生複雜且不規則的流動行為，藉此可有效的混合流體。此外，經由逐步地變動杜芬系統的參數，可獲得振盪週期為1Tp、2Tp、4Tp及8Tp的諧波（harmonic）電位與混沌電位，並將這些振盪電位應用到混合室壁面的四個電極上，以進一步地研究諧波與混沌振盪電場對流體流動特性及混合效率之影響。分析結果顯示，在電極上應用諧波振盪電位，可在混合室內產生週期的擾動效果，且隨著諧波電位振盪週期的增加，其擾動效果變的越來越複雜；若在電極上運用混沌振盪電位，則能在混合室內激起無週期的擾動效果。在這些週期性與非週期性的擾動行為作用下，能產生強烈的擾動效果，可有效的混合流體。
最後，結合主、被動式混合方案，以改善壓力驅動流之混合效率。在這個方法中，應用週期的擾動速度使流體在流道內產生類似波浪狀的摺疊效果，藉此可增加界面接觸面積；另外藉由在流道內加入波形結構，可進一步地增加界面接觸面積。分析結果顯示，延伸波形表面區段的長度與增加波形表面的幾何振幅及應用合適的Strouhal數，均能提高混合效率。

This dissertation focuses on the investigation of microfluidic mixers. Passive or/and active mixing schemes are used to improve the mixing efficiency in microfluidic mixers. The research consists of three main parts:
First, the mixing characteristics of electrokinetically-driven flow in microchannels with different wavy surface configurations are investigated for passive mixing schemes. In this mixing technique, wavy surfaces in the microchannels increase the interfacial contact area of the two species due to the two fluid streams traveling a contorted route while passing through the microchannel, hence improving the mixing efficiency. Numerical simulation results show that mixing efficiency can be improved by increasing the wave amplitude and/or the length of the wavy-wall section of the microchannel. Mixing efficiency is further enhanced by application of a heterogeneous surface charge pattern on the wavy surfaces. Results indicate that a heterogeneous surface charge pattern generates local flow circulation near the microchannel walls, significantly enhancing mixing efficiency.
Second, the effects of chaotic electric fields on the fluid flow characteristics within the microchannel and the consequent mixing effects in electrokinetically-driven flow are studied for active mixing schemes. In the proposed active mixing approach, chaotic oscillating electric potentials are applied to four electrodes mounted on the walls of the mixing chamber to perturb the fluid streams. The chaotic oscillating electric potentials are derived using the Duffing system. Results show that the chaotic oscillating electric potentials generate complex irregular flow behavior within the mixing chamber, resulting in efficient mixing of two species streams. Fluid flow characteristics within the microchannel and the corresponding mixing efficiency are further studied by applying harmonic and chaotic oscillating electric fields to the four wall-mounted electrodes in the mixing chamber. During simulation, harmonic electric potentials with oscillatory periods of 1Tp, 2Tp, 4Tp and 8Tp and chaotic electric potentials are derived via gradual variation of the parameters in the Duffing system. The results show that periodic perturbation effects within the mixing chamber are generated by applying harmonic oscillating electric potentials to the four electrodes. The perturbation effects become more and more complex as the oscillatory period of the harmonic electric potential increases. Aperiodic perturbation effects within the mixing chamber are created by applying chaotic oscillating electric potentials to these electrodes. These periodic and aperiodic perturbation behaviors generate strong perturbation effects which induce efficient species mixing.
Finally, a combined active and passive mixing scheme is used to improve the mixing efficiency of pressure-driven flows in microchannels. In the presented approach, periodic perturbations are applied to the velocity of the species streams at the microchannel inlets in order to introduce a wave-like folding effect within the microchannel, thereby increasing the interfacial contact area between the two species. Interfacial contact area is further increased by introducing a wavy-wall section within the downstream region of the microchannel. Results reveal that mixing efficiency can be enhanced by extending the length of the wavy-wall section, by increasing the geometric amplitude of the wavy surface, and also by applying a suitable Strouhal number to the periodic velocity perturbations.

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