互溶/不互溶流體於靜態混合器中混合的數值研究

Abstract

透過有限元素數值計算軟體COMSOL Multiphysics ，本文使用稀薄質傳法(Transport of Diluted Species)及水平集法(Level Set Method)來模擬SMX與Kenics靜態混合器在層流下的混合現象。就牛頓流體與非牛頓流體的流場與濃度場，經過詳細的定性與定量分析，本文的計算結果均與文獻中實驗結果相符。確認本文所發展之計算程序能作為靜態混合器的參數設計及研發工具；且就不互溶的兩股不同流體(如油與水)亦能進行混合分析。 於上述兩靜態混合器的混合情況，本文對不同擴散係數進行了參數分析以研究擴散與對流的相對效應。另經本文的研究，也獲得以下結論：(1)上述兩種數值計算方法皆能用於評估靜態混合中因複雜幾何結構混合元件所引發之對流效應及混合效果。就所需要計算資源而言，水平集法較稀薄質傳法高出許多；但前者能追蹤待混合之二相流液體介面之變化，能模擬不互溶流體的混合，更能觀察混合的實際物理現象。(2)SMX靜態混合器因其較複雜之幾何結構，其整體混合表現較Kenics 混合器佳。

Laminar mixing in SMX and Kenics static mixers was studied numerically using the method of transport of dilute species and level-set method, via the aid of COMSOL Multiphysics finite element software. Numerical results of both velocity and concentration fields of Newtonian and non-Newtonian fluids were examined qualitatively and quantitatively in details, and the validity was checked against experimental results in the literature. Thus, the method and numerical procedures developed in this thesis can be employed for the parametric study and design of static mixers. Furthermore, they can also be employed for studying mixing of immiscible fluids. As for the mixing of SMX and Kenics mixers, we have performed calculations with different mass diffusivities, for understanding the relative importance of convection and diffusion in the phenomenon. We also found: (1) Both the method of transport of dilute species and the level-set method can be employed for studying mixing in static mixers, but the level-set method needs much more intense calculation. However, the level-set method can track the interface between two fluids, and is capable to simulate the mixing of two immiscible fluids; it also provides more physical insight of mixing. (2) Due to the more complicated geometry of mixing element, the SMX mixers perform better mixing than that of the Kenics mixers.