Practical Approximate Method for the Analysis of the Flow of Polymer Melts

Abstract

In this study, we have tried to develop a practical approximate computer simulation of three-dimensional viscoelastic flow which requires reduced memory capacity and CPU time. A numerical simulation for two-dimensional tapered contraction flow with a converging angle was 60° was carried out using the Carreau model, a pure-viscous non-Newtonian model. The calculated results for the velocity field at γw=5.41s-1 almost agreed with those obtained by the PTT model which is a viscoelastic model which uses the Carreau viscosity model. We then examined an approximate method which uses stress field calculated by the PTT model and a velocity field obtained by the Carreau model. The shear stress and normal stress difference profiles obtained by this method agreed with the results obtained by the PTT model. It was found that this approximate method was effective in predicting the stress field of polymer melts in creeping flow where shear flow is governing. Because the velocity field of the pure-viscous non-Newtonian model was found to be suitable for creeping flow, a numerical simulation of the three-dimensional tapered contraction flow was carried out using the Carreau model. The numerical results for the stresses averaged over the width direction of the channel were compared with the experimental ones obtained by the flow birefringence technique. The normal stress differences did not agree with the experimental values, but the shear stress values were in near agreement. It was found that the shear stress could be simulated by a pure-viscous non-Newtonian model. Furthermore, we obtained velocity and stress profiles with consideration of the effects of the side walls, which were not obtainable in the two-dimensional flow simuration.