A study of turbulent mixing in a turbine-agitated tank using a fluorescence technique

Guillard, Fabrice; Trägårdh, Christian; Fuchs, László

doi:10.1007/s003480050382

Cited by 36 publications

(20 citation statements)

References 18 publications

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“…11. It may be observed that MI intensity is significantly higher in the discharge stream The above description of MI may be in contrast with the type of MI phenomena reported in literature for RDT and PBT impellers (Yianneskis et al, 1987;Haam et al, 1992;Guillard et al, 2000;Nikiforaki et al, 2003). A common factor amongst the aforementioned studies is that MIs persist close to the liquid surface, circulate around the shaft or form behind the baffles, whereas in the present case, the MIs have a relatively larger probability of occurrence in the discharge stream.…”

Section: Macro-instabilitiescontrasting

confidence: 74%

PIV study of the flow field generated by a sawtooth impeller

Unadkat

Rielly

Nagy

2011

Chemical Engineering Science

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Stereoscopic and high-speed particle image velocimetry (PIV) techniques have been employed to study the flow field induced by a sawtooth (EkatoMizer) impeller, operated in the fully turbulent flow regime at an impeller speed of 1500 rpm.Ensemble-averaged mean flow fields and turbulence quantities were calculated for a region close to the impeller blades. The flow was found to be anisotropic near the impeller and exhibited return-to-isotropy behaviour further away from it. Macroinstabilities were found to have a high probability of occurrence in the discharge stream. All three velocity components from the stereo-PIV measurements were used to estimate the dissipation rate, by adopting a large eddy simulation (LES) analogy.Spurious vectors distorting the dissipation rate calculation were identified, and various standard deviation filters were applied for vector validation. By evaluating the filtered dissipation rate profiles against the multi-fractal intermittency model of Meneveau and Sreenivasan (1991), the global standard deviation filter was found to be the most suitable type. The ratio of the maximum to the mean dissipation rate for the EkatoMizer discharge stream was found to be similar to that reported for Rushton disk turbine and pitched-blade turbine impellers in the literature, raising questions about the reported high-shear advantage of sawtooth impellers.

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Section: Macro-instabilitiescontrasting

confidence: 74%

PIV study of the flow field generated by a sawtooth impeller

Unadkat

Rielly

Nagy

2011

Chemical Engineering Science

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“…For a solid-liquid system (solid volume fractions up to 3.6%) agitated by a D = T/3 RT in turbulent regime (Re = 100,000 and 150,000) Derksen (2003) showed that the precessing vortex may help the resuspension of particles lying on the bottom of the tank, thus enhancing the mass transfer. 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).…”

Section: Effect Of Flow Instabilitiesmentioning

confidence: 99%

Flow Instabilities in Mechanically Agitated Stirred Vessels

Galletti¹,

Brunazzi²

2011

Hydrodynamics - Advanced Topics

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“…The square vessel is also filled with water to reduce light refraction at the interface. For more details on the geometry of the stirred tank used in this study see Guillard et al [3]. For the bubbly two-phase flow measurements, air bubbles are introduced, at a superficial gas velocity of 3.96×10 -4 m/s 50 mm below the bottom impeller, through a sparger with a diameter of 3D/4 with 30 active orifices at the chosen gas flow rate.…”

Section: Methodsmentioning

confidence: 99%

“…A value of 5 . 5 0 = P , determined by Guillard et al [3] for the same stirred reactor, was used in the present study.…”

Section: Introductionmentioning

confidence: 99%

Comparison of mixing between single- and bubbly two-phase systems in a Rushton stirred tank

Moghaddas

Revstedt

Trägårdh

et al. 2008

Advances in Fluid Mechanics VII

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Mixing is a widely practiced operation to effect distribution, intermingling and homogeneity of matter. Stirred tanks with different geometries (such as in main container tanks, impellers, baffles, etc.) are also widely used to mix different materials. The forces applied by impellers develop overall circulation or bulk flow. Superimposed on this flow pattern, there are turbulent eddies and also molecular diffusion of the fluids, which have a direct effect on the mixing phenomenon into the stirred tank reactors. In this work the mixing field in an aerated stirred reactor with two Rushton turbines was experimentally analysed using the particle image velocimetry technique (PIV). The mixing characteristics were measured at three different impeller rotational speeds: 225, 300 and 400 rpm, for both single-and bubbly two-phase mixing systems. The bubbles will, due to reflection and refraction of the laser light, cause an uneven and unknown distribution of light intensity in the measurement plane. This can be compensated for by introducing a second tracer with a known concentration. Based on this method the mixing of a determining tracer in liquid-phase in a double Rushton turbine stirred tank is studied. Using the PIV measurement technique and the flow structure of the liquid phase, the pumping capacity of those systems were calculated. The aerated-tounaerated relative power was also calculated from the experimental results and compared with the theoretical values. Reasonable agreement between experimental and theoretical results was obtained.

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A study of turbulent mixing in a turbine-agitated tank using a fluorescence technique

Cited by 36 publications

References 18 publications

PIV study of the flow field generated by a sawtooth impeller

PIV study of the flow field generated by a sawtooth impeller

Flow Instabilities in Mechanically Agitated Stirred Vessels

Comparison of mixing between single- and bubbly two-phase systems in a Rushton stirred tank

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