On the Flow of a Polymer Melt Passing Over a Transverse Slot

Abstract

The phenomenon of hole pressure occurs whenever a polymeric or viscoelastic liquid flows over a depression in a conduit wall. Numerical simulations undertaken for the flow of an aqueous polyacrylamide melt passing over a transverse slot arc considered here. The fluid model used for this study is a White-Metzner constitutive equation describing the non-Newtonian behavior of the melt. The results were computed by an elastic-viscous split-stress finite clement method (EVSS-FEM). a mixed finite clement method incorporating the non-consistent streamline upwind scheme. For verification, the numerical algorithm was first applied to compute the corresponding flow of the upper-convected Maxwell fluid model, a special case of the Whitc-Metzner model characterized by constant viscosity and relation time. The resulting hole pressure (Ph) was evaluated for various Deborah numbers (De) and compared with the analytical prediction derived from the Higashitani-Pritchard (HP) theory. The agreement was found to be satisfactory for creeping flow in the low De range, for which the HP theory is valid. Subsequently, the hole pressure of this flow problem was predicted. The streamlines and pressure distribution along the channel walls arc also presented. Furthermore, the effects of fluid elasticity, shear thinning, the exponent in the viscosity function and the relaxation-time function, and slot geometry on the hole pressure were investigated.

First normal stress difference measurements for polymer melts at high shear rates in a slit-die using hole and exit pressure data

“…Numerical simulation [9,14,15] and flow birefringence [10] both showed that the major assumptions (no flow in the hole and symmetry of the stress tensor about the center-line of the hole) in the HP theory are violated even at low shear rates. However, both types of studies showed that even with secondary flow in the hole, the stresses cancelled out in the integration of the stress field along the center-line (Eq.…”

Rheological Model and Transition Velocity Equation of a Polymer Solution in a Partial Pressure Tool

“…The analysis of the rheological characteristics of non-Newtonian fluids, such as polymer solutions, in specific tools, and the method of establishing the equation, can be used to deduce the rheological equation of a polymer solution in partial pressure tools, which is helpful for analyzing the influence of partial pressure tools on pressure drops in, and the apparent viscosity of, a polymer solution. Wu et al [16] used the White–Metzner constitutive model to describe the rheological properties of a polymer solution. A finite-element method was used to numerically solve the flow of the polymer solution through a single transverse groove, the pore pressure under different Deborah numbers was obtained, and the influence of fluid characteristic parameters and groove geometry on pore pressure was analyzed.…”