Berlin 2012 – wissenschaftliches Programm
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 37: Poster: Rheology (joint focus with DRG)
CPP 37.8: Poster
Donnerstag, 29. März 2012, 18:45–19:45, Poster A
Unsteady low Reynolds pipe number flows of a Carbopol solution: why the simplest flow problems still remain elusive? — Antoine Poumaere1, Miguel Moyers-Gonzales2, •Cathy Castelain1, and Teodor Burghelea1 — 1Universite de Nantes, CNRS, Laboratoire de Thermocinetique de Nantes, UMR 6607, La Chantrerie, Rue Christian Pauc, B.P. 50609, F-44306 Nantes Cedex 3, France — 2Department of Mathematics and Statistics, University of Canterbury, Private Bag 4800, Christchurch 8140, New Zealand
Carbopol solutions are often referred to as non-thixotropic "model yield stress fluids". It has been only recently shown that this picture does not suffice to tackle simple flow problems, particularly close to yield point (Putz et al., Phys. Fluids 20(3), 2008). The present study focuses on a equally simple flow configuration: a low Reynolds number unsteady pipe flow. Measurements of the unsteady velocity fields allow time-dependent measurements of the mean flow velocity, width of the viscoplastic plug, slip velocity and wall velocity gradients. The dependence of each of these quantities on the applied pressure drop reveals three distinct regimes: a solid regime corresponding to pressure drops significantly below the yield limit, a solid-fluid flow regime corresponding to intermediate flow regimes and a fluid regime far beyond the yield limit. Upon a decrease of the applied forcing a clear hysteresis in the dependence of each of the measured quantities on the applied pressure drop is observed. This finding comes into a perfect agreement with the yielding scenario recently proposed by Putz et al. (Rheologica Acta 48(6), 2009).