共押出進料區塊之三維有限元素法模擬

Abstract

共押出製程中之界面包覆及界面不穩定現象為影響多層薄膜及板材品質最重要之因素，故本文旨在使用Giesekus流變模型及於進料區塊壁面邊界採取滑動邊界設定以進行雙層共押出進料區塊內流動之三維有限元素模擬。由模擬結果可看出，相對於不滑動邊界，滑動邊界設定使壁面接觸線可在壁面上移動，能有效預測流體界面彎曲變化情形，且不會忽略壁面之影響。本文藉由改變Giesekus流變模型中之α參數探討因第二正向應力差造成之二次流動，結果顯示第二正向應力差對於界面包覆現象之影響極大。至於界面之正向應力差及剪切應力對於界面不穩定有極大之影響，故本文藉由分析雙層流體界面間之第一正向應力差及剪切應力以探討界面不穩定現象，結果顯示雙層流體之流量比及壁面光滑度為影響界面不穩定之重要因素。

In coextrusion process, the encapsulation phonomena and interfacial instabilities are the most important factors for the properties of multilayer films and sheets. In this study, three-dimensional finite element simulation of bicomponent coextrusion feedblock with Giesekus rheological model and slip boundary conditions imposed on the wall were discussed. Results show that in contrast to no-slip boundary conditions, slip boundary conditions would allow the displacement of contact line along the wall and have a more precise prediction of interface distortion without neglecting the wall effects. The formation of secondary flow due to the second normal stress difference was analyzed by varying the parameter α in Giesekus rheological model. Consequently, the simulation results show that the second normal stress difference have an great influence on the encapsulation phenomena. Meanwhile, first normal stress difference and shear stress at interface have a significant influence on the interfacial instability. In this study, the interfacial instabilities were investigated by analyzing the first normal stress difference and the shear stress between both fluids. Results indicate that the flow ratio of the both fluids and slip over the upper and lower wall of the feedblock have a crucial effect on the interfacial instabilities.