基于Cross方程的IUPAC-LDPE熔体挤出胀大的数值模拟

Numerical simulation of extrudate swell of the IUPAC-LDPE melt by using Cross model

挤出胀大是聚合物挤出成型加工中的常见问题。文中数值模拟了用Cross模型表征的IUPAC-LDPE熔体经过长圆口模的挤出胀大流动,计算采用的是基于常规四边形单元的有限元法。广义牛顿流体模型中的Cross模型能较好地描述IUPAC-LDPE熔体的剪切黏度稀化特性,但该方程不能预测出与挤出胀大实验相近的挤出胀大比,同时该方程预测的出口压力损失基本上为常数。本文的结果表明工程上常用的Cross型广义牛顿流体模型不能用于分析和预测真实聚合物熔体的挤出胀大行为。

Extrudate swell is a common problem in polymer extrusion processing. The numerical simulation of extrusion swelling of the IUPAC-LDPE melt through a long circular die was carried out by using Cross model and finite element method with the normal quadrilateral element. The Cross model in the generalized Newtonian fluid models can well describe the shearthinning viscosity property of the IUPAC-LDPE melt. However, Cross model can not predict the swell ratios similar to the experimental values, and at the same time, the predicted exit pressure drops of the model are almost constant. The present resuits show that the Cross-type generalized Newtonian fluid model usually used in engineering can not be used to analyze and predict the swelling behavior of the realistic polymer melt.