於液滴微流體進行二相微溶現象的實驗與數值研究

Abstract

我們使用了三維計算流體力學數值模型於流動聚焦裝置內，研究了二相微溶液滴微流體系統的質傳現象，並且透過水與正丁醇的液滴實驗將數值模型進行了驗證。其中數值模型為使用Volume of Fluid方法，並且透過user defined function將彼相間的質傳關係加入商業軟體的求解器之中，而由於其中液滴溶解的過程是由兩相界面上的濃度差異所驅使，因此我們使用菲克擴散來計算數值模型的質傳量。為了證明上述的成果，我們在大範圍的操作流率下，將數值結果與實驗結果進行了適應性分析，還詳細討論了滴流 (dripping)的液滴生成機制，並且量化討論了液滴溶解的質傳過程，接著研究了液滴在非對稱的彎曲流道的流動下，其溶解濃度與流場間的交互關係。結果說明，在滴流的液滴生成機制下，為球狀頭部堵住通道後，使得交叉流的速度在頸部產生極大值，進而造成交叉流的加速來夾斷液滴，而對於不同的操作流量條件下，使用較小的流量比有較高的質傳效率，並且我們發現，在非對稱流動的彎曲流道內，可經由交替變化的翼展向流動，使得的其傳質效率與直線流道相比能夠再提升20 %。未來，此模型能夠用來研究二相液-液微溶液滴微流體系統的質傳關係，並且對於實驗設計參數與其機理上能夠更加瞭解。

We present three-dimensional computational fluid dynamics study to investigate the mass transfer phenomenon of miscible drops in a flow focusing device. Numerical results are compared with experimental data. In the present numerical model, the volume of fluid method is used, and the mass transfer model between phases is implemented to the commercial flow solver through the user defined function. As the dissolution process is driven by the concentration gradient, we use Fickian diffusion to calculate the mass transfer rate. The formation mechanism of drops in the dripping regime is discussed in detail. Numerical and experimental results are analyzed under a wide range of operating flow rates. Then the mass transfer process of the drops is quantitatively discussed. Moreover, we conducted numerical simulations to investigate the flow inasymmetric curved channels and the interaction between the concentration and the flow field. We found that, in the curved channel, the transfer efficiency is raised by about 20% through alternating direction of the spanwise flow. In the future, this present model can be used to study the transfer between two-phase liquid-liquid miscible drop and to help obtain better design parameters for experiments.