A study on the instability of coherent mixing structures in a continuously stirred tank

Guillard, Fabrice; Trägårdh, Christian; Fuchs, László

doi:10.1016/s0009-2509(00)00201-3

Cited by 34 publications

(24 citation statements)

References 16 publications

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“…Guillard et al (2000a) carried out LIF experiments on a stirred tank equipped with two RT observing large time scale oscillations of the concentration, induced by an interaction between the flows from the impeller and a baffle. They argued that circulation times can be altered when the flow direction changes, the turbulence levels measured with stationary probes can be significantly broadened and thus can provide an erroneous interpretation of the true levels of turbulence in a tank, and mixing in otherwise quiescent regions can be significantly enhanced due to the presence of flow variations (Guillard et al, 2000b). Knoweledge of true levels of turbulence is needed for the optimum design of micro-mixing operations (as in cases of chemical reactions).…”

Section: Effect Of Flow Instabilitiesmentioning

confidence: 99%

Flow Instabilities in Mechanically Agitated Stirred Vessels

Galletti¹,

Brunazzi²

2011

Hydrodynamics - Advanced Topics

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Section: Effect Of Flow Instabilitiesmentioning

confidence: 99%

Flow Instabilities in Mechanically Agitated Stirred Vessels

Galletti¹,

Brunazzi²

2011

Hydrodynamics - Advanced Topics

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“…Mixing time was observed to change by 20% when the tracer was injected inside the precessional vortex core. Guillard et al (2000) used concentration data inside a Rushton-impeller STR to identify large scale mixing structures. They showed that at higher impeller speed (i.e., at turbulent regime) the mixing structures become unstable and the tracer is convected faster within the tank volume.…”

Section: Introductionmentioning

confidence: 99%

Flow structure and the effect of macro-instabilities in a pitched-blade stirred tank

Roy

Acharya

Cloeter

2010

Chemical Engineering Science

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“…Despite Planar Laser Induced Fluorescence (PLIF) having been used to assess mixing in many systems (Adams and Barigou, 2007;Alberini et al, 2014;Guillard et al, 2000;Hu et al, 2010;Hu et al, 2012;Law and Wang, 2000;Szalai et al, 2004) the application of the technique to viscoelastic fluids is limited. Stokes & Boger (Stokes et al, 2001) studied the mixing performance of swirling flows using PLIF, highlighting the presence of different elastic regimes in a simple geometry.…”

Section: Figure 1: Typical Butterfly Impellermentioning

confidence: 99%

Mixing of Newtonian and viscoelastic fluids using “butterfly” impellers

Ramsay

Simmons

Ingram

et al. 2016

Chemical Engineering Science

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The mixing of high viscosity and viscoelastic fluids may be performed in industry using a "butterfly" impeller, which has received scant attention. This paper describes the characterisation of these impellers using both Newtonian and viscoelastic (Boger) fluids with an identical base viscosity under laminar flow conditions in batch tanks without baffles. Measurements are made using two rotational speeds (N = 30 or 60 rpm) over a wide range of impeller to tank diameter ratios from 0.53 to 0.98.Particle Image Velocimetry (PIV) and Planar Laser Induced Fluorescence (PLIF) have been used to determine local velocity fields, shear rates, flow numbers and mixing times respectively, with impeller power number Po obtained from torque measurements. A down-pumping flow pattern is observed, with maximum normalised velocities of 25% of the impeller tip speed observed in the axial plane, increasing to 60% in the rotational plane due to solid body rotation. Angle resolved measurements found these to be slightly increased as the impeller passes the image plane, with viscoelastic fluids displaying a greater uniformity of velocity across the image planes due to elastic energy storage. Maximum shear rates are greatest between the impeller and the wall, yet remain low i.e. O (10) s -1 . Mixing times obtained from PLIF show that mixing times in viscoelastic fluids show a slight reduction compared to the Newtonian equivalent. The impeller power number was determined as Po = 0.6 in the turbulent regime, while the laminar constant K p and the Metzner-Otto constant k s were equal to 122 and 16.0 respectively. Highlights: "Butterfly" impellers used for processing of viscoelastic fluids. Low impeller Power number Po due to low blade area. Maximum shear rates of 17 s -1 in region between impeller and wall at N = 60 rpm. Mixing times longer in viscoelastic fluids due to elastic effects.

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A study on the instability of coherent mixing structures in a continuously stirred tank

Cited by 34 publications

References 16 publications

Flow Instabilities in Mechanically Agitated Stirred Vessels

Flow Instabilities in Mechanically Agitated Stirred Vessels

Flow structure and the effect of macro-instabilities in a pitched-blade stirred tank

Mixing of Newtonian and viscoelastic fluids using “butterfly” impellers

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