Laminar entry flow of viscoelastic fluids

Abstract

The behaviour of viscoelastic fluids in entry region flow is of importance in the polymer processing industry, for example, in extrusion. A fundamental undertanding of the flow characteristics will permit a more scientific approach to equipment specification and design. This dissertation comprises an extensive review of the literature on laminar entry flow, and the presentation of the results of a comprehensive experimental study of the laminar flow of viscoelastic polymer solutions through abrupt circular contractions. A significant volume of work has appeared in the literature, concerned with various aspects of entry flow. The behaviour of Newtonian fluids in hydrodynamic entrance regions has been well established. Inelastic shear thinning fluids have, in general, undergone sufficient investigation. However, the literature does not contain adequate quantitative experimental data on viselastic entry region flow, especially in regard to fluid property characterisation. The experimental investigation described in this thesis was concerned with the nature of the flow patterns and velocity profile rearrangements in the region upstream of abrupt axisymmetric contractions. The test fluids used were aqueous solutions of Separan, a partially hydrolysed polyacrylamide, and Carbopol, carboxypolymethylene. The fluid properties were characterised by measuring the visometric shear stree and first normal stress difference, using and R-16 model Weissenberg rheogoniometer, over a shear rate range of 1.11 to 1112 sec¯¹. The test fluids showed similar shear thinning properties, but exhibited significant variation in the level of fluid elasticity. [...]