Authors: Simon J Haward Jeffrey A Odell
Publish Date: 2004/02/04
Volume: 43, Issue: 4, Pages: 350-363
Abstract
A novel approach is presented to study the benchmark problem of flow around spheres in model dilute solutions of monodisperse samples of atactic polystyrene in dioctyl phthalate Spheres are held “stationary” on flexible cantilevers of known springconstant k while the polymer solutions are pumped past at controlled flow rates allowing access to a wide range of Deborah number In this way the nonNewtonian forces experienced by the spheres can be measured as a function of Deborah number while detailed observations and measurements of birefringence are made enabling assessment of macromolecular strain and orientation In addition the flow field around a sphere has been measured in an aPS solution Experiments have been performed on a single sphere and on two spheres axially aligned in the direction of flow The extensional flow around the downstream stagnation point of the single sphere is found to play a pivotal role in the development of molecular strain and stress resulting in flow modification and subsequent nonNewtonian behaviour The flow birefringence in the wake is found to modify severely the flow around a second downstream sphere affecting the nonNewtonian forces encountered by the second sphere This provides an explanation for the time interval dependent terminal velocity often observed when two spheres follow the same path through viscoelastic liquids
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