Circular Die Swell Evaluation of LDPE Using Simplified Viscoelastic Model
Simplified viscoelastic model based finite element method was presented to evaluate circular die swell of LDPE. Differential viscoelastic models were firstly described for the incompressible viscoelastic flow with isothermal extrusion, and simplified viscoelastic model (SVM) was then selected for viscoelstic component in extra stress terms. Discrete elastic viscous stress splitting (DEVSS) method was used to stabilize elliptic term in momentum equations. Mini–element method for hexahedral element was applied to stabilize equal order velocity pressure interpolation. Interface–tracking approach was used to detect the position and moving of the free surface at extrudate region. In experiment, circular die was selected to study LDPE extrusion flow. The measured viscoelastic properties were employed as input data in LDPE flow simulation. CCD camera was used to capture extrudate swell. Simplified viscoelstic model was then used to predict extrudate swell in three flow rate conditions, 100, 264, and 490 mm3/s. Compared with experimental results, the die swell predicted by SVM were 1.37%, 2.37%, and 5.5% different, for the three flow rate conditions, respectively. The results showed that simplified viscoelastic model could be employed to predict circular die swell.