- 學位論文
平面方波式微混合器中運用邊界凸出塊之流場研析
Prediction of Mixing Flowfield in a Planar Square-Wave Micromixer with Boundary Protrusions
摘要
被動式微混合器(Passive Micromixers)內的混合主要是倚賴分子擴散與混沌對流兩種機制達成，由於此微流裝置屬於微尺寸範圍，因此混合流場現象以層流為主。不同的流體在各種幾何形狀中可藉由分流、延伸、摺疊、分裂與重新結合等過程,來達到有效的混合流動。本研究目的在探討配置邊界凸出塊之平面式方波型微混合器混合增益特性；數值計算中先假設流體為不可壓縮，可溶混層流，且忽略重力的影響與溫度的變化。理論模型建立於三維暫態之質量、動量、及物種傳輸守恆方程式，並採用SIMPLEC 演算法於求解統御方程式以計算各流場參數。數值預測結果與已有參考文獻之不同軸向位置、雷諾數的混合影像、效率等實驗觀察和量測數據相比較，來驗證計算流體力學軟體的正確性。本文並模擬微混合器不同條件下預測混合流場的壓力阻，計算結果發現混合器內鄰近邊界凸出塊的橫截方向呈現旋渦和二次流，故沿流動路徑引起混合效率增大的效果。文中另以數值模擬改變邊界凸出塊的形式，長度，寬度和位置以探討對平面式方波型微混合器混合效率的影響，以達成裝置最佳化設計。
並列摘要
The mixing process in a passive micromixer depends mostly on molecular diffusion and chaotic advection due to the dominating laminar flow nature on the microscale. The appropriate design of channel geometric shapes is crucial to split, stretch, fold, break-up and recombine the flows for effective mixing of different fluids. This paper describes the mixing flow characteristics of two working fluids that flow through a planar square-wave micromixer with protruded boundary structures. The analysis treats the fluids as laminar, incompressible, isothermal and miscible liquid flows with the constant properties. The theoretical model consists of a set of unsteady three-dimensional conservation equations of mass, momentum and species concentration. The governing equations are numerically solved using an iterative semi-implicit method for pressure-linked equations consistent algorithm to resolve the flow and transport variables. To validate the computer software, the predicted mixing parameters at different axial locations and Reynolds numbers were compared with the measured data in the literature. The present study also examined the mixing flowfield as well as the pressure drop across a micromixer. The simulated results indicated that intense vortices and secondary flows in spanwise planes were induced near the boundary protrusion regions to augment mixing efficiency along the flow path. To optimize the micromixer design, numerical experiments were extended to examine the effects that alter the shape, length, width and placement of boundary protrusions during mixing enhancement of a planar square-wave micromixer.