Numerical simulations of Boger fluids through different contraction configurations for the development of a measuring system for extensional viscosity
Journal article, 2012

This paper reports the flow behaviour of Newtonian and Boger fluids through various axisymmetric contraction configurations by means of numerical predictions. A principal aim has been to evaluate the geometrical design choice of the hyperbolic contraction flow. The FENE-CR model has been used to reflect the behaviour of Boger fluids, with constant shear viscosity, finite (yet large) extensional viscosity and less than quadratic first normal stress difference. Numerical calculations have been performed on six different contraction configurations to evaluate an optimized geometry for measuring extensional viscosity in uniaxial extensional flow. The influence of a sharp or rounded recess-corner on the nozzle has also been investigated. Few commercial measuring systems are currently available for measurement of the extensional rheology of medium-viscosity fluids, such as foods and other biological systems. In this context, a technique based on the hyperbolic contraction flow would be a suitable alternative. The pressure drop, the velocity field, the first normal stress difference and the strain rate across the geometry have each been evaluated for Newtonian and Boger fluids. This numerical study has shown that the hyperbolic configuration is superior to the other geometry choices in achieving a constant extension rate. In this hyperbolic configuration, no vortices are formed, the measuring range is broader and the strain rate is constant throughout the geometric domain, unlike in the alternative configurations tested. The difference between sharp and rounded recess-corner configurations proved to be negligible and a rise in excess pressure drop (epd) for increasing deformation rates has been observed.

Hyperbolic contraction flow

strain-hardening fluids

excess

rheology

Viscoelastic fluid

elongational viscosity

finite volume/element method

Extensional viscous flow

shear

polymer melts

pressure-drop

semi-hyperbolic die

viscoelastic flows

rheometer

Author

Magda Nyström

SIK – the Swedish Institute for Food and Biotechnology

H. R. T. Jahromi

Swansea University

Mats Stading

Chalmers, Materials and Manufacturing Technology, Polymeric Materials and Composites

M. F. Webster

Swansea University

Rheologica Acta

0035-4511 (ISSN) 14351528 (eISSN)

Vol. 51 8 713-727

Subject Categories

Materials Engineering

Areas of Advance

Materials Science

DOI

10.1007/s00397-012-0631-0

More information

Latest update

8/24/2018