Numerical Analysis of Elongation Behavior of Melt Flow in Contraction Channels with Cylindrical Barriers

The flow of polymer melt in contraction channels with cylindrical barriers was numerically simulated. A commercial LDPE melt was considered, and the rheological property of the melt was represented using the Extended Pom-Pom model (XPP). The simulation was performed with various barrier configurations, and the effects of the barriers were investigated extensively in relation to the efforts to clarify the phenomenon of melt fracture mitigation by the addition of filter or porous medium. It can be observed that the addition of barriers modifies significantly the flow fields in the region near the contraction. Investigation of the elongation stress shows that the addition of barriers increases the stress in the region near the contraction, but decreases the elongation rate and elongation stress in the region at the upstream of the contraction and induces the undershoots of elongation rate and elongation stress in the region at the downstream of the contraction. With the increase in Weissenberg numbers, these effects are more significant for the channels with two barriers as compared to that with single barrier. The reduction of elongation rate and elongation stress should play an important role in the mitigation of the upstream instability, which in turn mitigates the gross melt fracture.