蜿蜒型流道之三維速度場與濃度場同步量測分析

Abstract

本文以蜿蜒型微反應器為模型，使用一種新式量測方法同步剖析流體在其中流動時的三維濃度場與速度場，達到迅速且完整分析流場資訊的目的；將實驗量測與模擬的結果相互比較後，發現由實驗結果計算所得之混合指數普遍低於數值模擬之結果，且此數值差異隨著流體移動距離增加益加明顯，由此可知螢光粒子在微反應器中的擴散情形以及混合效能受到粒子間互相聚集以及流道壁面沾黏的影響甚巨，因而呈現了數值模擬中無法預期的實驗變數。 微流體元件的分析方法可分為數值模擬驗證與新式量測技術應用兩個主要部分；數值模擬驗證方面是以商用軟體CFD-ACE建立完整的流道模型，利用調控進口處流速改變雷諾數，以此為控制變因分別分析蜿蜒型微反應器內部的流線軌跡、速度場與濃度場在不同雷諾數條件下之情形；量測技術的應用分為染料混合實驗以及三維同步量測兩個部分: 染料混合實驗以定性觀測流場變化為主要目的，拍攝不同截面上的混合影像，以影像的三原色變化趨勢作不同雷諾數下混合效能的比較；三維同步量測中包含速度場與濃度場的建立，速度場的建立是將 micro-PIV技術與雷射誘發螢光術結合，以連續方程式為運算依據將PIV軟體(Insight 5, TSI Inc.)計算所得的二維速度場作後處理，搭配合理的邊界條件假設取得流場中的三維速度向量；三維濃度場的建立則以二元化之粒子計數法結合分水嶺法，正確計算穩態流場中單位空間內之粒子數量，並根據蜿蜒型微流體元件本身之濃度回歸曲線，推測得知流場中各部位的濃度場分佈情形。 本文的特色為新式量測技術實際應用與速度場三維分析方法的建立，透過共軛焦顯微術具有優勢的光學切片能力，獲取實驗中真實的三維流場資訊，其定量化的能力有利於驗證模擬結果，預期此量測方法將對未來各式微反應器的設計與分析上提供一種新的選擇。

The purpose of this thesis is to apply a newly invented simultaneously measuring technique to a planar serpentine microreactor, and to construct the whole flow field, including three-dimensional concentration and velocity field, inside the microreactor. The confocal microscopy and micro-PIV (micro particle image velocimetry) techniques are combined to obtain the concentration information and velocity data in-plane. By stacking up velocity data in different focal planes, the three-dimensional velocity vectors can be determined based on the continuity equation. Flow fields of low Reynolds number are fully constructed and verified with the numerical simulation. The three-dimensional velocity measurement outcome shows great consistency with the simulation results. Due to the accelerating and centrifugal effect of serpentine geometry, the out-of plane velocity component is observed in both the measurement and the simulation. Mixing index of Re = 0.04 and 0.1 are calculated through the concentration data obtained by particle counting method. However, a noticeable amount of difference is shown in the mixing index calculations comparing with numerical simulation. The results suggest that there are actually some unpredictable variables, such as particle aggregation, particle adhesion to walls, and clogging problems, in experimental tests. Mixing efficiency of microreactors may be excessively estimated if designers ignore these crucial factors. The application of a novel simultaneously measuring technique and the construction method of three-dimensional flow field inside a microreactor are demonstrated in this article. The combination of these techniques provides a useful and reliable tool to analyze flow conditions inside microreactors of biomedical use.