Numerical simulation of converging flow of polymer melts through a tapered slit die

Abstract

Numerical simulation of the converging flow of polymer melts through a tapered slit die was performed with the finite element method using two kinds of constitutive equations: the Phan Thien-Tanner (PTT) and the Giesekus models with a single relaxation time. The calulated stress distributions assuming planar flow were compared with the experimental values measured by the flow birefringence technique. The model parameters were determined from the experimental data of shear viscosity and the primary normal stress difference by fitting the models. The PTT model fitted the experimental data better than the Giesekus model within the range of experimental shear rates, and therefore the numerical results of stress distribution for the PTT model agreed with the experimental values better than those for the Giesekus model. The difference between the calculated and experimental local stresses for the PTT model was less than 20% of the values at the downstream slit wall and it can be concluded that the PTT model is useful for the simulation of converging flow of polymer melts in the low shear rate region. Moreover the average stresses over the width of the channel in the fully developed rectangular channel flow were compared with the experimental values in order to assess the effect of side wall in the experiment. As a result, the average stresses in the rectangular channel flow were closer to the experimental values than those in the planar flow. It was found that the numerical results may be closer to the experimental results by considering the three-dimensional flow.