Vortex depth in unbaffled single and multiple impeller agitated vessels

Markopoulos, Joannis; Kontogeorgaki, Eleni

doi:10.1002/ceat.270180113

Cited by 36 publications

(20 citation statements)

References 6 publications

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“…However, the free surface profiles predicted by these models qualitatively agree well with that estimated using a correlation given by Markopoulos and Kontogeorgaki (1995). 23 In Fig. 2, we can see that the water surface profiles are unsteady due to the transient nature of the free-surface hydrodynamics in the stirred tank.…”

Section: Profiles Of the Liquid Surfacementioning

confidence: 94%

Free Surface Turbulent Flow in an Unbaffled Stirred Tank: Detached Eddy Simulation and VOF Study

Yang¹

2015

Chem. Biochem. Eng. Q.

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Numerical simulations based on the RANS model are known to have drawbacks of low accuracy in predicting the turbulence quantities of the flow fields in stirred tanks. For this purpose, the detached eddy simulation (DES) model was employed to simulate the turbulent flow in an unbaffled dish-bottom stirred tank. The free-surface deformation was modelled by the volume of fluid (VOF) 11. The results show that the predicted surface profiles using the combination of DES and VOF are generally better than their counterparts obtained by the k-ε model. The mean velocity components and turbulent kinetic energy are in good agreement with the experimental results. By comparison, the differences between the k-ε predictions and the LDV data are much greater. These findings indicate that DES works better than k-ε model in the prediction of the free-surface hydrodynamics in stirred tanks.

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Section: Profiles Of the Liquid Surfacementioning

confidence: 94%

Free Surface Turbulent Flow in an Unbaffled Stirred Tank: Detached Eddy Simulation and VOF Study

Yang¹

2015

Chem. Biochem. Eng. Q.

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“…When the impeller is rotating, a vortex will develop on the surface of the liquid. Many investigators [7][8][9]11 have found that there are two types of motion in the flow of a liquid agitated by a mixer. A zone with a constant angular velocity (vortex zone) is formed in the central part of the vessel, and a zone where the peripheral velocity of the liquid decreases according to the hyperbolic law (irrotational zone) is formed in the remaining part.…”

Section: Theoretical Considerationsmentioning

confidence: 99%

“…The tangential component of velocity (v t ) is continuous in r but a break appears at r 0 . Assuming that the axial flow is very small and therefore negligible in comparison with the tangential liquid flow and there is no contribution from the continuity equation 8 , the r and z components of the equation of motion can be expressed as 7,14 :…”

Section: Theoretical Considerationsmentioning

confidence: 99%

“…For example, the central vortex is effective in drawing down floating solid particles or in removing gas bubbles from the liquid, thus reducing foam formation. The absence of baffles in a vessel typically results in the generation of a central vortex and a swirling flow 8 . Also, baffles are usually omitted in the case of very viscous fluids where, as a result of giving rise to dead zones, they may actually worsen the mixer performance.…”

Section: Introductionmentioning

confidence: 99%

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Rao¹,

Kumar²,

Patel³

2009

ScienceAsia

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Agitating liquids in an unbaffled surface aeration tank leads to the formation of a vortex in the region of the impeller shaft. The types and characteristics of the vortex govern the process phenomena of a surface aeration tank. In the present work, experimental results and empirical correlations have been obtained to relate the vortex depth to a number of physical factors. Experiments have been carried out on geometrically similar surface aeration systems, so that the present results can be simulated in the field conditions. The critical speed at which the vortex reaches the impeller has been estimated. It is found that around critical speed, there is an observable change in mass transfer characteristics, power used for mixing, and radius of the forced vortex zone. Equations for predicting vortex depth in geometrically similar surface aeration tanks have also been developed.

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“…Study of the formation of vortex in an unbaffled stirred tank is very important to understand the air-entrainment at particular power consumption. So, study of vortex formation caused by an unbaffled condition of the system is closely associated with power consumption in the system as it is widely known that the unbaffled system consumes less power [4,5] than the baffled system. Therefore, study on vortex formation in agitated vessels to save energy in terms of power consumption is required [6].…”

Section: Introductionmentioning

confidence: 99%

Vortex Depth Analysis in an Unbaffled Stirred Tank With Concave Blade Impeller

Devi¹,

Kumar²

2017

ChChT

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Abstract. 1 The present study was carried out by experimenting in a stirred tank of unbaffled system employed with concave blade impeller. In this study the influence of impeller diameter (d), tank diameter (D) and impeller clearance depth ( C ) on vortex depth is investigated at various impeller rotational speeds. The higher vortex depth is observed when the impeller is closer to the tank bottom. Relative vortex depth increases with the increase in the impeller diameter in all cases of impeller clearance depth at constant D. Smaller tank diameter gives higher relative vortex depth, when d is constant at different impeller clearance depths. Critical speed is found decreasing with the increase in C/D and d/D ratio. Finally, a scale up criteria for relative vortex depth has been developed, which is valid for geometrically similar conditions.

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Vortex depth in unbaffled single and multiple impeller agitated vessels

Cited by 36 publications

References 6 publications

Free Surface Turbulent Flow in an Unbaffled Stirred Tank: Detached Eddy Simulation and VOF Study

Free Surface Turbulent Flow in an Unbaffled Stirred Tank: Detached Eddy Simulation and VOF Study

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Vortex Depth Analysis in an Unbaffled Stirred Tank With Concave Blade Impeller

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