- 學位論文
雙流體混合機制之數值模擬及實驗分析
Numerical Simulation and Experimental Analysis of Chaotic Mixing in Two-Fluid Flow
摘要
本文以數值模擬及實驗量測研究雙流體的混合，建立流體混合的定量化標準，瞭解流體混合的影響因素；繼而模擬雙流體在蜿蜒渠道中的混合，並實際設計、製作並量測流體混合的結果。對於相溶的流體，混合的組成以濃度的標準差表示；對於不相溶的流體，比表面積越大，流體的接觸面積越大，混合得越均勻，以灰階影像擷取、統計相鄰畫素差異得到。兩相流體混合的組成，計算粒子的相對距離，擷取灰階影像、影像修正、反相處理、影像矩陣化、粒子定量化、統計粒子相對距離得到。在微尺度環境下，流體的雷諾數很低，難以擾動方式混合流體；本文改良平面轉折的蜿蜒渠道，使其橫截面積交錯變化，增加局部的壓力梯度，以產生回流。結果顯示流速越快，渠道橫截面積的比率越大，使得Dean number 變大，Dean vortices越強烈，流體的運動軌跡及流體介面也大幅扭曲及拉伸；配合適合的入口分佈，流體可以迅速達到混合。在雷諾數102以下，流體的速度不因為流經重複形狀的渠道而放大擾動；然而流體的運動軌跡，卻會因為角落Dean vortices的存在，扭曲程度不斷增加。在雷諾數0.87，截面積比率兩倍時產生的混合效果較一般蜿蜒渠道增加32%。而在雷諾數13.9時，增加47%。若流體的密度不同，基於動量平衡，密度大的流體趨向低速區域。在雷諾數16，Dean number 12.27時，0.5 %的密度差異即產生明顯的分離現象。綜合而言，本文從定量標準、原理探討、數值模擬，流體晶片設計製作到實驗量測，完成了微尺度雙流體混合的研究。
並列摘要
This work finishes two-fluid mixing via numerical simulation and experimental measuremet. Mixing indexes, mixing mechanism, mixer of a planar serpentine channel with alternating cross sections is designed, simulated, and verified. Mixing indexes for miscible fluids, immiscible fluids, and two-phase fluids are designated as the standard deviation of concentration, interface to volume ratio, and the sum of interval of particles. Fast flow or great ratio of cross sections increases the pressure gradient and the Dean number. In coordinate with a suitable inlet fluid distribution, fluid mixing can be promoted. Below Reynolds number 102, flow velocity does not perturbed by experiencing a repeated channel; but the trajectory does. At Reynolds number 0.87, for aspect ratio 2, the increased mixing degree is 32% as compared to the serpentine channel; for Reynolds number 13.9, it rises up to 47%. For fluids of different densities, to keep momentum balance, the heavy fluid trends to locate at the region of slow flow. At Reynolds number 16 and Dean number 12.27, a difference of 0.5% makes apparent separation. Overall, this work has great contribution on microscale two-fluid mixing in process of mixing indexes analysis, mechanism of fluid mixing, numerical simulation of fluid mixing, fabrication of fluidic mixer, and measurement of fluid mixing.