本研究目的為探討不同氣體與氧氣在T型微混合器內的混合情況，以數值模擬軟體ANSYS CFX與PSP(Pressure Sensitive Paints)螢光壓力感測塗料進行分析，討論不同氣體在微混合器內依層流與捲入流範疇可區分成不同的流動狀態，以及混合情況。本研究討論改變入口流速，觀察在特定流動狀態下不同氣體特性對混合效應的影響。本研究使用兩個不同寬度之微混合器，寬度分別為550、350 μm，流道深度為125 μm，流道深寬比為0.23與0.36，兩入口流道長度皆為5 mm，主流道長度為10 mm。微混合器結構使用黃光微影製程製作，利用熱壓印機在105 ℃加壓2 kg/m^2將此結構壓印至PMMA壓克力片上，並利用熱壓法將壓克力片黏合，製作出T型微混合器。
本研究選擇之混合氣體組合為氮氣-氧氣、氬氣-氧氣、氦氣-氧氣，入口流速範圍為3 m/s~50 m/s (Re_(O_2 )=36.1~600.9，Pe=7.7~489.9)。實驗結果顯示，入口流速為15 m/s (Re_(O_2 )=199.4，Pe=147.0)前混合由擴散作用主導，流速為3 m/s (Re_(O_2 )=39.9，Pe=27.8)於寬度為550 μm的氦氣-氧氣在出口處的混合效率為96.44%，氮氣-氧氣混合效率為76.03%，而氬氣-氧氣混合效率最差為72.46%，混合效率與擴散係數成正向關係。隨著流著流速提升，氣體分子擴散時間縮短，混合效率隨著流速升高而下降。使用寬度為350 μm的微混合器，因深寬比較高，氣體分子間的擴散距離縮短，且流道側向剪應力使氣體分子滯留的效果變強，混合效率較寬度550 μm的好，在寬350 μm的微混合器，流速為3 m/s (Re_(O_2 )=36.1，Pe=27.8)時氮氣-氧氣的混合效率提升至98.40%。而高流速下，當氣體分子進入捲入流的範疇。流體翻轉大幅增加彼此接觸面積，混合效應增強，混合效率隨著流速提高而上升。從實驗觀察到氬氣-氧氣於寬350 μm的微混合器在入口流速30 m/s (Re_(O_2 )=360.5，Pe=293.9)開始進入捲入流，混合效率為58.20%，超越氮氣-氧氣53.78%的混合效率，當流速提高到50 m/s (Re_(O_2 )=600.9，Pe=489.9)，氬氣-氧氣的混合效率大幅提升至90.45%，而氮氣-氧氣僅提升至60.07%。發生捲入流的雷諾數與流體靜黏滯係數成反向關係，氬氣靜黏滯係數較大較早進入捲入流。若使用寬度550 μm的微混合器，則氬氣-氧氣在Re_(O_2 )=398.7才進入捲入流的範疇，因流道深寬比較小，流道上下壁面較大，會抑制渦漩的發展而延後捲入流的發生。氦氣-氧氣因密度差異過大無法形成對稱渦漩，在兩個不同寬度的微混合器皆無法觀察到流體翻轉的現象，故氦氣-氧氣的混合效率隨流速增加而下降。最後將實驗與模擬進行比對，兩者在層流狀態下具有良好的一致性，在捲入流狀態下實驗得到的氧氣濃度分佈偏離模擬結果，因模擬將表面設定為光滑壁面，與實驗所差異，但發生捲入流的雷諾數實驗與模擬具有良好的一致性。

The purpose of this study is to investigate gases mixing inside T-type micromixers. Both numerical simulation using ANSYS CFX and experimental approach with PSP (Pressure Sensitive Paints) are applied to analyze the oxygen concentration and fluid field inside the micromixers. Due to the different flow velocity in the micromixers, the fluid field is distinguished to different flow regimes: laminar flow regime and engulfment flow regime. The effect of gases properties on mixing effect has been observed in specific flow regimes and discussed. The height of the micromixers is 125 μm and the width used in this study are 550 μm and 350 μm, therefore, their aspect ratio are 0.23 and 0.35, respectively. The length of two gas inlet channels are the same as 5 mm, while mixing channel is set as 10 mm. The structures of micromixers are fabricated by soft photolithography. The pressure (2 kg/cm^2) and temperature (105 ℃) are applied to make the structure on the PMMA sheets with hot embossing. The micromixer is constructed by combing two PMMA sheets with thermal fusion bonding.
Three sets of gases mixing are investigated in this study, and they are Nitrogen-Oxygen, Argon-Oxygen, and Helium-Oxygen. The inlet velocities of two gas flow are the same and controlled from 3 m/s to 50 m/s (Re_(O_2 )=36.1~600.9, Pe=7.7~489.9). The detailed oxygen concentration inside the micromixers are measured by using PSP sensor with different gases mixing. The experiment results show that the mixing effect is dominated by the molecular diffusion when inlet velocity is less than 15 m/s (Re_(O_2 )=199.4, Pe=147.0). For inlet velocity is 3 m/s (Re_(O_2 )=39.9, Pe=27.8), the mixing efficiency of Helium-Oxygen at the exit of 550 μm wide micromixer is 96.44%, which is greater than 76.03% of Nitrogen-Oxygen. The mixing efficiency of Argon-Oxygen is 72.46%, and it is the lowest compared to others. The gases with higher diffusion coefficient with oxygen molecules will have better mixing efficiency. It is also observed that the mixing efficiency decreases with increase of inlet velocity due to the reduced diffusion time of gases. As 350 μm wide micromixers are used, namely with the higher aspect ratio, the diffusion distance becomes shorter and the residence time of gases become longer by stronger shear stress. Therefore 350 μm wide micromixers have better mixing performance compared to 550 m wide micromixers. For inlet velocity of 3 m/s (Re_(O_2 )=36.1, Pe=27.8), mixing efficiency of Nitrogen-Oxygen has improved to 98.40% in the 350 μm wide micromixer, greater than that (76.03%) in the 550 μm wide micromixer. If inlet velocity is increased to higher than 30 m/s (Re_(O_2 )=360.5, Pe=293.9), the fluid field of Argon-Oxygen mixing changes to engulfment regime. Gas mixing is enhanced as the interfacial area of gases increases due to twisting of two gases in engulfment regime. Mixing efficiency of Argon-Oxygen is 58.20%, higher than 53.78% of Nitrogen-Oxygen. When the inlet velocity further increases to 50 m/s (Re_(O_2 )=600.9, Pe=489.9), mixing efficiency of Argon-Oxygen enhances to 90.45%, much higher than 60.07% of Nitrogen-Oxygen. The Reynolds number triggering fluid flow into engulfment regime has inverse relation with dynamic viscosity of the fluid. It is observed that the fluid field of Argon-Oxygen changed into engulfment regimes earlier than Nitrogen-Oxygen due to the higher dynamic viscosity of Argon. In addition, the fluid field of Argon-Oxygen mixing in 550 μm wide micromixer does not change into engulfment regime until Re_(O_2 )=398.7 while the 350 mm wide micromixer triggered earlier at Re_(O_2 )=360.5. Because the wider micromixer has larger surface at the upper and bottom walls, it will slow the development of vortices and delay the development of the engulfment flow. Engulfment flow is not observed inside both 350 m and 550 m micromixers for Helium-Oxygen mixing in the inlet velocities varying from 3m/s to 50 m/s and only asymmetry vortices has been observed at higher velocity due to the great difference of density between Helium and Oxygen. Therefore, mixing efficiency of Helium-Oxygen will not increase as inlet velocity increases at higher inlet velocity conditions. Finally, the experiment data acquired by PSP technique and simulation calculated with ANSYS CFX have good agreement in the laminar flow regime. The profiles of oxygen concentration obtained from experimental method deviate from simulation data in the engulfment flow regime, and it is attribute to the surface condition which is assumed smooth in the simulation. However, the critical Reynolds number triggering the engulfment flow shows favorable agreement in the experiment and simulations.

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