新型半主動式微型混合器之研發

Abstract

本實驗研究目的在於提出新型微型混合器：混合器本身首先具有一般被動式微型混合器結構簡單的特性，其次因為本實驗工質乃具有磁化特性之奈米磁性流體，其具有可控制性，所以只要外加磁場作用，將可期待類似磁棒轉動或者互拉推擠的效果產生，這些現象都是主動式微型混合器特有優勢。綜合以上兩種微型混合器的優點，本實驗研究將利用外加磁鐵，取代一般主動式混合制動器的地位，搭配簡易蜻蜓式（Dragonfly）微流道結構，流體於微流道內部因被動式結構將先形成液珠，接著藉由媒介油基磁性流體受磁鐵磁化影響，對液珠產生主動式互拉推擠作用，不需要額外持續耗能，即可提升混合效率，在此，吾人將本新研究發展之設計稱為「半主動式微混合器」（Semi-Active Micromixer）。 論文首先進行媒介工質即奈米磁性流體之製作改良，應用田口法找尋最佳化水基磁性流體製作參數，研究顯示水基磁性流體在不同的實驗環境下，對流體本身特性會造成影響，研究採用三種控制因子(流體倒入方式、攪拌時加溫性、油酸氨保護)進行實驗，最後分析磁化結果顯示：採用鐵離子酸液滴定氫氧化鈉鹼液溶液中、平台攪拌時設定加溫90℃、油酸與氨各以5mg：5mg配置為其最佳化，而最後配置出來的水基磁性流體與油基磁性流體其皆具有超順磁性。水基於莫耳濃度0.05M磁場強度13500 Oe下，磁化強度可達0.96emu/g，油基在磁場強度13500 Oe下其莫耳濃度分別為0.5M、0.25M、0.125M，磁化強度可達7.98emu/g、6.56emu/g、4.73emu/g。 決定好磁性流體之配置後，其次利用微機電製程技術進行微型混合器製作，使用黃光製程製作SU-8光阻模仁，並利用PDMS轉印微流道結構，最後接管翻模並接附於玻璃上即完成本實驗微型混合器。最終實驗目的在於研究新型混合器之混合效率，入口管道各別注入油基磁性流體、無色去離子水及藍染劑水，實驗結果顯示，單一磁性流體濃度在單一磁場強度下，液珠本身依靠擴散作用整體混合隨著流道往下游混合越均勻，同一種流體濃度以中央相同特徵距離來看，混合均勻度隨著磁場強度增強而越均勻，相同磁場強度下，混合均勻度隨磁性流體濃度增大而混的較均勻。

The purpose of this essay is to propose a novel micro-mixer. The structure of the proposed mixer is as simple as that of the traditional passive mixer. Furthermore, the working flow of this assay is a kind of controllable nano-magnetic fluids therefore it can be twisted or squeezed like a magnetic rod once an external magnetic field is applied. To combine the advantages mentioned above, instead of an active mixer, an external magnet is employed in our research. With the simple dragonfly type of micro-fluidic channel, the fluid can be formed as the droplet shape by this passive structure. The oil-based agent magnetic working fluid is magnetized to squeeze the droplets and enhance the mixing efficiency. This type of mixer is called a “Semi-Active Micromixer”. First we focus on the refinement of the agent of nano-magnetic fluids. The results show that different experimental environments have effects on the characteristics of the fluid by using Taguchi method. Three controlled parameters, the way of pouring, the way of heating, and the modification of the Ammonium Oil acid are tested for the experiments. The optimal conditions are as follows. (1). Use Fe ionized solution to titrate the sodium hydroxide solution. (2). Stir the mixing fluid at 90 oC. (3). Adopt 5 mg: 5 mg as the proportion of oleic acid and ammonia. The magnetization is 0.96emu/g for optimal water-based magnetic fluids of 0.05M. The magnetization is 7.98emu/g, 6.56emu/g and 4.73emu/g for oil-based magnetic fluids of 0.5M, 0.25M, 0.125M respectively at the external magnetic filed of 13500 Oe. All the ferrofluids illustrates the characteristic of superparamagnety. The MEMS process and soft lithography technique were employed to fabricate the micro-mixer device.The final results of the experiments focus on the mixing efficiency of the novel mixer. The oil-based magnetic fluid, transparent DI water and the blue dye are injected through the inlets respectively. The resultes show that: (1).The mixing uniformaity is more stable as closer to the end the microchannel when the same concentration of the magnetic fluid is applied. (2).The mixing is more uniform when stronger magnetic field is applied. (3).The mixed fluid is more uniform when the concerntration of the magnetic fluid is higher.