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1
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Replay to Comments onFlow characteristics of axial high speed impellers(Chem. Process Eng., 2010, 31, 661)

100%
Fořt I.
Chemical and Process Engineering
|
2012
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vol. 33
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issue 2
317-318
2
Content available remote

A study on blending characteristics of axial flow impellers

63%
Fořt I., Jirout T.
Chemical and Process Engineering
|
2011
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vol. 32
|
issue 4
311-319
EN
This paper presents an analysis of the blending characteristics of axial flow high-speed impellers under a turbulent regime of flow of an agitated low viscosity liquid. The conductivity method is used to determine the time course of blending (homogenisation) of miscible liquids in a pilot plant fully baffled mixing vessel, and a torquemeter is used for measuring the impeller power input in the same system. Four-blade and six-blade pitched blade impellers and three high efficiency axial flow impellers are tested for the given degree of homogeneity (98%).The experimental results and also the results of the authors' previous study, in accordance with the theoretical approach described in the literature, show that there is a universal relationship between the impeller power number and the dimensionless blending time, taking into consideration the impeller-to-vessel diameter ratio, independent of the geometry of the axial flow impeller but dependent on the degree of homogeneity. This relationship is found to be valid on a pilot plant scale under a turbulent flow regime of an agitated liquid.
3
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Modelling of the Bubble Size Distribution in an Aerated Stirred Tank: Theoretical and Numerical Comparison of Different Breakup Models

51%
Kálal Z., Jahoda M., Fořt I.
Chemical and Process Engineering
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2014
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vol. 35
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issue 3
331-348
EN
The main topic of this study is the mathematical modelling of bubble size distributions in an aerated stirred tank using the population balance method. The air-water system consisted of a fully baffled vessel with a diameter of 0.29 m, which was equipped with a six-bladed Rushton turbine. The secondary phase was introduced through a ring sparger situated under the impeller. Calculations were performed with the CFD software CFX 14.5. The turbulent quantities were predicted using the standard k-ε turbulence model. Coalescence and breakup of bubbles were modelled using the MUSIG method with 24 bubble size groups. For the bubble size distribution modelling, the breakup model by Luo and Svendsen (1996) typically has been used in the past. However, this breakup model was thoroughly reviewed and its practical applicability was questioned. Therefore, three different breakup models by Martínez-Bazán et al. (1999a, b), Lehr et al. (2002) and Alopaeus et al. (2002) were implemented in the CFD solver and applied to the system. The resulting Sauter mean diameters and local bubble size distributions were compared with experimental data.
4
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CFD Prediction of Gas-Liquid Flow in an Aerated Stirred Vessel Using the Population Balance Model

51%
Kálal Z., Jahoda M., Fořt I.
Chemical and Process Engineering
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2014
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vol. 35
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issue 1
55-73
EN
The main topic of this study is the experimental measurement and mathematical modelling of global gas hold-up and bubble size distribution in an aerated stirred vessel using the population balance method. The air-water system consisted of a mixing tank of diameter T = 0.29 m, which was equipped with a six-bladed Rushton turbine. Calculations were performed with CFD software CFX 14.5. Turbulent quantities were predicted using the standard k-ε turbulence model. Coalescence and breakup of bubbles were modelled using the homogeneous MUSIG method with 24 bubble size groups. To achieve a better prediction of the turbulent quantities, simulations were performed with much finer meshes than those that have been adopted so far for bubble size distribution modelling. Several different drag coefficient correlations were implemented in the solver, and their influence on the results was studied. Turbulent drag correction to reduce the bubble slip velocity proved to be essential to achieve agreement of the simulated gas distribution with experiments. To model the disintegration of bubbles, the widely adopted breakup model by Luo & Svendsen was used. However, its applicability was questioned.
5
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CFD simulation of turbulent velocity field in the discharge streem from a standard Rushton turbine impeller

51%
Kysela B., Fořt I., Konfršt J.
Czasopismo Techniczne
|
-
PL
The velocity field around the standard Rushton turbine was investigated by the Computational Fluid Dynamics (CFD) calculations and compared with results obtained from the Laser Doppler Anemometry (LDA) measured in a pilot plant baffled cylindrical vessel. For calculations the Large Eddy Simulation (LES) approach was employed. The impeller motion was modeled using the Sliding Mesh technique (SM). The mean ensemble-averaged velocity profiles and root mean square values of fluctuations were compared in the radial discharge jet from the standard Rushton turbine under turbulent regime of flow of agitated liquid. There were found two subregions in the discharge stream and the values of the axial profiles of the radial component of the fluctuating velocity are rather same determined from the LES calculations and from the LDA measurements in the second one ZEF (zone of established flow) of the impeller discharge stream, but they differ in the first region ZFE (zone of flow establishment) in the impeller vicinity, although they exhibit the same shape. The impeller power number derived from calculations shows also good agreement with values introduced in literature with a significant influence of the thickness of the impeller disc.
6
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A Study of CFD Simulations of the Flow Pattern in an Agitated System with a Pitched Blade Worn Turbine

51%
Skočilas J., Fořt I., Jirout T.
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vol. 34
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issue 1
39-49
EN
This paper presents a numerical analysis of an agitated fully baffled cylindrical vessel with a down pumping four blade worn or unworn pitched blade impeller (α = 45° and 30°) under a turbulent flow regime. CFD simulations predict the pumping capacity of the system equipped by worn and unworn pitched blade impeller. Experimental data were taken from the authors’ previous work and compared with results of numerical computations. A good agreement with experimental data was obtained. The ensemble-average mean velocity field with worn and unworn impellers was computed. It follows from the simulation results that the wear rate of the impeller blade has a significantly negative effect on the velocity distribution in an agitated liquid. The greater the destruction of the worn blade, the higher is the deformation of the velocity field around the rotating impeller, with a simultaneous decrease in impeller pumping capacity.
7
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Study of the Turbulent Flow Structure around a Standard Rushton Impeller

45%
Kysela B., Konfršt J., Fořt I., Kotek M., Chára Z.
Chemical and Process Engineering
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2014
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vol. 35
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issue 1
137-147
EN
The velocity field around the standard Rushton turbine was investigated by the Laser Doppler Anemometry (LDA) and Particle Image Velocimetry (PIV) measurements. The mean ensembleaveraged velocity profiles and root mean square values of fluctuations were evaluated at two different regions. The first one was in the discharge stream in the radial direction from the impeller where the radial flow is dominant and it is commonly modelled as a swirling turbulent jet. The validity range of the turbulent jet model was studied. The second evaluated region is under the impeller where flow seems to be at first sight rather rigorous but obtained results show nonnegligible values of fluctuation velocity.
8
Content available remote

BLENDING CHARACTERISTICS OF HIGH-SPEED ROTARY IMPELLERS

45%
Fořt I., Seichter P., Pešl L., Rieger F., Jirout T.
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vol. 34
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issue 4
427-434
EN
This paper presents a comparison of the blending efficiency of eight high-speed rotary impellers in a fully baffled cylindrical vessel under the turbulent flow regime of agitated charge. Results of carried out experiments (blending time and impeller power input) confirm that the down pumping axial flow impellers exhibit better blending efficiency than the high-speed rotary impellers with prevailing radial discharge flow. It follows from presented results that, especially for large scale industrial realisations, the axial flow impellers with profiled blades bring maximum energy savings in comparison with the standard impellers with inclined flat blades (pitched blade impellers).
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