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Impact of thixotropy on flow patterns induced in a stirred tank : numerical and experimental studies

Couerbe, Grégory and Fletcher, David F. and Xuereb, Catherine and Poux, Martine Impact of thixotropy on flow patterns induced in a stirred tank : numerical and experimental studies. (2008) Chemical Engineering Research and Design, vol. (n° 6). pp. 545-553. ISSN 0263-8762

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Official URL: http://dx.doi.org/10.1016/j.cherd.2007.11.010

Abstract

Agitation of a thixotropic shear-thinning fluid exhibiting a yield stress is investigated both experimentally and via simulations. Steady-state experiments are conducted at three impeller rotation rates (1, 2 and 8 s−1) for a tank stirred with an axial-impeller and flow-field measurements are made using particle image velocimetry (PIV) measurements. Threedimensional numerical simulations are also performed using the commercial CFD code ANSYS CFX10.0. The viscosity of the suspension is determined experimentally and is modelled using two shear-dependant laws, one of which takes into account the flow instabilities of such fluids at low shear rates. At the highest impeller speed, the flow exhibits the familiar outward pumping action associated with axial-flow impellers. However, as the impeller speed decreases, a cavern is formed around the impeller, the flow generated in the vicinity of the agitator reorganizes and its pumping capacity vanishes. An unusual flow pattern, where the radial velocity dominates, is observed experimentally at the lowest stirring speed. It is found to result from wall slip effects. Using blades with rough surfaces prevents this peculiar behaviour and mainly resolves the discrepancies between the experimental and computational results.

Item Type:Article
Additional Information:This publication is available at http://www.sciencedirect.com/science/journal/02638762
Audience (journal):International peer-reviewed journal
Uncontrolled Keywords:
Institution:Other partners > University of Sydney (AUSTRALIA)
Université de Toulouse > Institut National Polytechnique de Toulouse - INPT
Université de Toulouse > Université Paul Sabatier-Toulouse III - UPS
French research institutions > Centre National de la Recherche Scientifique - CNRS
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Deposited By: Martine POUX

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