Numerical Simulation of the Exit Flow for the Viscoelastic Fluids

Abstract

The nature of viscoelastic flow near the exit of a nozzle is dependent die swell phenomena and various polymer processing operations such as fiber spinning, sheet forming, blow molding, etc. Although many calculations have been performed by various investigators, the local values of stresses have seldom been compared experimentally and numerically. In the present paper, the exit flow is analyzed by the finite element method. The constitutive equations used in the simulations are the Phan Thien-Tanner (PTT) type model of a viscoelastic fluid with shear thinning viscosity, the Oldroyd-B model of a viscoelastic fluid with constant viscosity, the power-law model of a pure viscous fluid with the shear thinning viscosity, and the Newtonian model. The stress distributions and swelling ratios are compared among these models, and the effects of shear thinning viscosity and elasticity on the exit flow are considered. It is found that swelling ratio decreases as the shear thinning effect of viscosity becomes stronger, and increases with the elastic effect. The swelling mechanism can be explained mostly from the viewpoint of stress. The calculated results of stress distributions by the PTT type model are compared with the experimental values measured by means of the flow birefringence technique. The stress distributions calculated are found to be in agreement with the experimental values, but the estimation of swelling ratio is insufficient.