Effects of shear thinning fluid rheological properties on IMR radius in laminar stirred tanks

Gopal, K, Bhattacharjee, P and Parthasarathy, R 2015, 'Effects of shear thinning fluid rheological properties on IMR radius in laminar stirred tanks', in Asia Pacific Confederation of Chemical Engineering Congress 2015: APCChE 2015, incorporating CHEMECA 2015, Melbourne, Australia, 27 September - 1 October 2015, pp. 670-677.


Document type: Conference Paper
Collection: Conference Papers

Title Effects of shear thinning fluid rheological properties on IMR radius in laminar stirred tanks
Author(s) Gopal, K
Bhattacharjee, P
Parthasarathy, R
Year 2015
Conference name Asia Pacific Confederation of Chemical Engineering Congress 2015: APCChE 2015, incorporating CHEMECA 2015
Conference location Melbourne, Australia
Conference dates 27 September - 1 October 2015
Proceedings title Asia Pacific Confederation of Chemical Engineering Congress 2015: APCChE 2015, incorporating CHEMECA 2015
Publisher Engineers Australia
Place of publication Melbourne, Australia
Start page 670
End page 677
Total pages 8
Abstract The formation of isolated mixing regions (IMRs) in laminar stirred tanks has been a topic of interest for many years to the chemical engineering industry. In many viscous fluids these unmixed regions exist as toroidal vortices; one located above and the other below the impeller, and can occupy a large volume of the tank, significantly reducing the degree of homogeneity achievable. A lack of understanding of the formation of IMRs yields many challenges in predicting their existence and eliminating them from mixing vessels. The literature indicates a knowledge gap for IMRs in non- Newtonian fluids, which form the majority of those encountered in chemical engineering industries. Experiments were conducted in a laminar stirred tank, with a liquid height to diameter ratio of 1:1 and a four bladed Rushton turbine located at half the liquid height. Flow visualisation with acid/base neutralisation was employed to investigate IMR formation in shear thinning carboxymethyl cellulose (CMC). The radii of the IMR above and below the impeller were measured at a set Reynolds number and mixing time for various concentrations of CMC and analysed as a function of the corresponding apparent viscosities. The results showed that as viscosity increases, the radii of the IMRs both above and below the impeller increase, until a certain viscosity at which IMR radii then begin to decrease, and at a faster rate. This transition between IMR size increasing and decreasing with viscosity coincides with the inception of rod climbing and flow reversal; whereby fluid flow directions in the vessel reverse.
Subjects Chemical Engineering not elsewhere classified
Keyword(s) flow reversal
isolated mixing regions
laminar
non-Newtonian
rheology
shear-thinning.
ISBN 9781922107473
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