本研究以數值方法模擬不同性質流體在微流道中混合的情形, 探討雷諾數、幾何結構, 流體性質和支流道位置對混合效果的影響。首先, 就不同離散方法比較其模擬結果差異, 其結果顯示數值擴散造成的影響非常大, 因此求解速度和濃度場時, 需選用高階離散方法來減少數值擴散產生。在選定模擬方法之後, 改變微流道幾何結構, 以加入擋板的方式, 觀察流場變化及混合特性, 加入擋板可以
延長流體在流道停留的時間, 增加流體間分子擴散的效果, 在高雷諾數時更可產生迴流, 攪拌流體使混合強度提高。接著再將側壁注入流體改為甘油水溶液, 藉由改變甘油含量來觀察不同流體性質(如密度, 黏滯力和擴散係數) 下, 其混合行為之差異。在高雷諾數下, 倘若甘油水溶液質量分率增加, 注入口雷諾數則會變小, 因此擋板後產生迴流的範圍也隨之減小。而低雷諾數時, 分子擴散為流體混合的主要因素, 故混合效果隨著擴散係數的大小而增減。最後再嘗試改變支流道注入位置, 在高雷諾數時, 將支流道設在迴流產生處有助於流體混合。

In this thesis, the fluids mixing process of different fluid properties in a microchannel is studied numerically. The effects of Reynolds number, geometric structure, fluid properties and location of sidewall injection in mixing efficiency are investigated. At first, compare the different of discretization methods, with the results that the numerical diffusion had a great influence on it. Therefore, we must choose a high-order discretization scheme to solve the velocity and concentration profile. Then, we set baffles in the microchannel and observe the change of flow field and mixing characteristic. Inserting baffles can extend the staying period of fluids, and expand molecular diffusion as well. Furthermore, it can induce recirculation which stirring the fluids to rise the mixing intensity in high Reynolds number. Afterwards, we replace the sidewall injection fluid with a solution of glycerol in water. By varying the glycerol content of the glycerol/water solution, the variation in mixing behavior with changes in the difference in the properties of two fluids (e.g., viscosity, dnesity and diffusivity) was investigated. As the glycerol content increase, Reynolds number wolud decrease as well as the range of recirculation. Molecular diffusion is the main factor in low Reynolds number. For this reason, the increased mixing efficiency would follow the increase of diffusivity. At last, we change the location of sidewall injection next to the recirculation area and we found that is helpful for the fluid mixing in high Reynolds number.

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