層流攪拌器流體混合研究

Abstract

對於黏滯性較高的流體混合，由於功率消耗的限制，一般常使用尺寸較大，但轉速 較慢的攪拌器，因而流場屬於層流，針對此本計畫擬以數值方式探討層流式攪拌器的攪 拌過程，將包括螺桿(screw impeller)及螺帶(helical ribbon impeller)兩種形式，所使用的 流體包含牛頓及非牛頓流體。數值方法方面，將採用近幾年來我們所發展的使用非結構 性網格的有限體積法。為處理葉片的旋轉，將使用多重參考座標系。對於非牛頓流體將 採用Carreau 模式。另外為應付複雜的幾何形狀，將採用多重區塊的方法建立網格。針 對各種幾何參數將詳細的探討其對功率的消耗,、誘發循環的流量、及混合的能量等的影 響，將瞭解流體混合中詳細的動態過程。全程計畫分兩年完成，頭一年以螺桿式攪拌器 為主，第二年將探討螺帶式，同時將比較此兩種攪拌器於暫態混合的動態表現。

For mixing of highly viscous fluids it is often to use agitators being large in size but rotating at low speeds to avoid the requirement of large power consumption. Therefore, the agitating flow field is in laminar regime. In this project numerical methods are employed to study the mixing flow in laminar agitating systems. Two types of agitators will be under consideration: screw impellers and helical ribbon impellers. Both the Newtonian and non-Newtonian fluids will be included as working fluids. The numerical procedure used for analysis is a finite volume method applicable to unstructured grids developed in our group in the past years. To cope with the rotation of the impeller the multi-frame of reference will be incorporated into the governing equations. For the non-Newtonian fluids the model of Carreau will be adopted. In addition, we will use the multi-block method to generate grids for such a complex geometry encountered in the mixing tank. The effects of various geometric parameters on the agitating performance will be tested. The performance of the agitating system will be examined in terms of power requirement, induced circulating flow rate, and mixing energy. The dynamic process during mixing of fluids will also be examined in details. The project will be completed in two years. In the first year we are concerned with the screw type agitator. In the following year the ribbon type will be the concern and comparison of the dynamics of the mixing process between the two type agitators will be made.