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Enhanced mixing of Newtonian fluids in a stirred vessel using impeller speed modulation
Author(s) -
Yek Wei M.,
NouiMehidi Mohamed N.,
Parthasarathy Rajarathinam,
Bhattacharya Sati N.,
Wu Jie,
Ohmura Naoto,
Nishioka Nami
Publication year - 2009
Publication title -
the canadian journal of chemical engineering
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.404
H-Index - 67
eISSN - 1939-019X
pISSN - 0008-4034
DOI - 10.1002/cjce.20231
Subject(s) - reynolds number , mechanics , rushton turbine , mixing (physics) , impeller , amplitude , newtonian fluid , sine wave , non newtonian fluid , waveform , square wave , physics , mathematics , materials science , control theory (sociology) , optics , computer science , turbulence , control (management) , voltage , artificial intelligence , quantum mechanics
This paper reports on an experimental study of mixing intensification using speed modulation of a six‐blade Rushton turbine in a stirred vessel. Mixing times were measured using a non‐intrusive technique based on direct visualisation of an acid‐base reaction in a Newtonian fluid. The impeller speed modulation was achieved by using two waveforms: a square wave and a sine wave. The amplitude was fixed between a maximum Reynolds number of Re max = 60 and minimum Reynolds numbers of Re min = 40 or 30. The wave periods were varied (10, 20, or 40 s) in order to compare the effects of unsteady stirring on mixing performance. It was observed that a square wave protocol with the shortest wave period and the larger amplitude resulted in the shortest time to destroy the observed isolated mixing regions (IMRs), which are known to exist in stirred vessels operating at low Reynolds number. However, the sine wave protocol led to a slow diffusive mechanism in which IMR structures reached an asymptotic volume and remained visible even after several hours. The results are presented and discussed using digital photographs taken at different time intervals during experimentation.