The stability of viscoelastic fluids in complex flows : the role of shear and extensional rheology

Understanding the flow of polymeric fluids is important for optimizing commercial processes such as injection molding and fiber spinning. The combination of streamwise curvature and elastic normal stresses can lead to the onset of elastic flow instabilities, severely rate-limiting such processes. This thesis focuses on the stability of two complex non-Newtonian flows of dilute polystyrene solutions: the viscometric flow between a rotating cone-and-plate and the flow through an axisymmetric contraction-expansion. Torsional shear flows of elastic fluids with closed streamlines can accumulate heat from viscous dissipation resulting in spatial nonuniformities in the temperature profile and viscometric properties. In this thesis, a detailed study of the effect of viscous heating on the steady shearing of elastic fluids between a rotating cone-and-plate is performed. The relative importance of viscous heating and elasticity can be quantified by a new dimensionless thermoelastic number. This parameter is a fluid material property which is a function of polymer molecular weight, geometry and temperature. As the thermoelastic number is increased, strong temperature gradients reduce the elasticity of the test fluid and delay the onset of the instability, eventually stabilizing the flow completely. The flow of elastic fluids into an axisymmetric abrupt contraction-expansion is a complex flow containing regions of both shear and extension that tests the limits of current viscoelastic constitutive models.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Mechanical Engineering.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2001

Author dc:creator

• Rothstein, Jonathan P. (Jonathan Philip), 1974-

Advisor dc:contributor.advisor

• Gareth H. McKinley.

• Mechanical Engineering.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/8926

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/8926