Flow-induced birefringence study of secondary flow in entrance region of rectangular slit channel for long-chain-branched polyethylene melt

Abstract

This work presents an analysis of the inner boundary of the secondary flow (i.e., corner vortex flow) in the entrance region of a rectangular slit channel for long-chain-branched polyethylene melt evaluated using particle tracking and stress-induced birefringence measurements. Further, the flow-induced birefringence technique was used to investigate the effects of temperature and shear rate on the size of the secondary entry flow. Obtained results and trends were compared with the laser-Doppler velocimetry data taken from the open literature for the same polymer melt and comparable flow conditions. Interestingly, the results of both methods were very similar. This suggests that the stress-induced birefringence measurements may be a useful tool for investigating secondary entry flows of polymer melts.