Turbulence Characteristics in a Rushton Stirring Vessel: A Numerical Investigation
DOI:
https://doi.org/10.51983/ajsat-2013.2.2.758Keywords:
Mixing, Stirring tank, Turbulence, DPIV, FLUENT, Rushton turbineAbstract
Understanding of the flow in stirred vessels can be useful for a wide number of industrial applications, like in mining, chemical and pharmaceutical processes. Remodeling and redesigning these processes may have a significant impact on the overall design characteristics, affecting directly product quality and maintenance costs. In most cases the flow around the rotating impeller blades interacting with stationary baffles can cause rapid changes of the flow characteristics, which lead to high levels of turbulence and higher shear rates. The flow is anisotropic and inhomogeneous over the entire volume. A better understanding and a detailed documentation of the turbulent flow field is needed in order to design stirred tanks that can meet the required operation conditions. This paper describes an effort for accurate estimation of the velocity distribution and the turbulent characteristics (vorticity, turbulent kinetic energy, dissipation rate) in a cylindrical vessel agitated by a Rushton turbine (a disk with six flat blades). Results from simulations using FLUENT (a commercial CFD package) are compared with Time Resolved Digital Particle Image Velocimetry (DPIV) for baseline configurations in order to validate and verify the fidelity of the computations. Different turbulent models are used in this study in order to determine which one is the most appropriate. Subsequently a parametric analysis of the flow characteristics as a function of the clearance height of the impeller from the vessel floor is performed. Results are presented along planes normal or parallel to the impeller axis, displaying velocity vector fields and contour plots of vorticity turbulent dissipation and others. Special attention is focused in the neighborhood of the impeller region and the radial jet generated there. The present results provide useful information for the design of the mixing process as well as for more accurate estimations in future work.
References
Derksen, J., and Van den Akker, H. E. A., 1999, “Large Eddy Simulations on the Flow Driven by a Rushton turbine”, A.I.Ch.E. Journal., 45, (2), pp. 209-222
Alcamo, R., Micale, G., Grisafi, F., Brucato, A., and Ciofalo, M., “Large-eddy simulation of turbulent flow in an unbaffled stirred tank driven by a Rushton turbine”, 2005, Chem. Eng. Sci., 60, pp. 2303-2316
Lamberto, D. J., Muzzio, F. J., Swanson, P. D., and Tonkovich, A. L., 1996 “Using Time-Dependent RPM to Enhance Mixing in Stirred Vessels”, Chem. Eng. Sci., 51, pp. 733-741.
Bakker, A., and Van den Akker, H. E. A., 1994 “Single-phase flow in stirred reactors”, Trans. I.Chem.E., 72, pp. 583-593
Yeho, S. L., Papadakis, G., and Yianneskis, M., “Numerical Simulation of Turbulent Flow Characteristics in a Stirred Vessel Using the LES and RANS Approaches with the Sliding/Deforming Mesh Methodology”, 2004, Trans I.Chem.E., Part A, Chem. Eng. Res. Des., 82, (A7), pp. 834-848
Van’t Riet, K., Bruijin, W., and Smith, J. M., 1976, “Real and Pseudo Turbulence in the Discharge Stream from a Rushton Turbine”, Chem. Eng. Sci., 31, pp. 407-412
Sharp, K. V., and Adrian, R. J., “PIV Study of Small Scale Flow Structure around a Rushton Turbine”, 2001, A.I.Ch.E. Journal., 47, (4), pp. 766-778
Zhou, G., and Kresta, S. M., 1996, “Impact of Tank Geometry on the Maximum Dissipation rate for Impellers”, A.I.Ch.E. Journal., 42, (9), pp. 2476-2490
Bhattacharya, S., and Kresta, S. M., 2002, “CFD Simulations of Three Dimensional Wall Jets in a Stirred Tank”, Can. J. Chem. Eng., 80, pp. 1-15
Kresta, S. M., and Wood, P. E., 1991, “Prediction of the Three- Dimensional Turbulent Flow in Stirred Tanks”, A.I.Ch.E. Journal., 37 (3), pp. 448-460
Jenne, M., and Reuss, M., 1999, “A critical assessment on the use of k-ε turbulence models for simulation of the turbulent liquid flow induced by a Rushton-turbine in baffled stirred-tank reactors”, Chem. Eng. Sci., 54, pp. 3921-3941
Micheletti, M., Baldi, S., Yeoh, S. L., Ducci, A., Papadakis, G., Lee, K. C., and Yianneskis, M., 2004, “On Spatial and Temporal Variations and Estimates of Energy Dissipation”, Trans I. Chem.E., Part A, Chem. Eng. Res. Des., 82, (A9), pp. 1188-1198
Ranade, V. V., “An Efficient Computational Model for Simulating Flow in Stirred Vessels: A Case of Rushton Turbine”, 1997, Chem. Eng. Sci., 52, (24), pp. 4473-4484
Ranade, V. V., Perrard, M., Le Sauze, N., Xuereb, C., and Bertrand, J., 2001, “Trailing Vortices of Rushton Turbine: PIV Measurements and CFD Simulations with Snapshot Approach“, Chem. Eng. Res. Des., 79, (A), pp. 3-12
Ranade, V. V., 2002, “CFD Predictions of Flow near Impeller Blades in Baffled Stirred Vessels: Assessment of Computational Snapshot Approach”, Chem. Eng. Comm., 189, pp. 895-922
Bakker, A., and Oshinowo, L. M., 2004, “Modeling of Turbulence in Stirred Vessels using Large Eddy Simulations”, Chem. Eng. Res. Des., 82, (A9) pp. 1169-1178
FLUENT Inc. FLUENT 6 Users Guide, published by FLUENT Inc., Lebanon, New Hampshire, USA, 2005.
FLUENT Inc. GAMBIT Users Guide, published by FLUENT Inc., Lebanon, New Hampshire, USA, 2004.
FLUENT Inc. MIXSIM Users Guide, published by FLUENT Inc., Lebanon, New Hampshire, USA, 2003
Durbin, P. A., and Petterson Reif, B.A., 2001, “Statistical Theory and Modeling for Turbulent Flows”, John Wiley & Sons, LTD, Chapter
Paul, E. L., Atiemo-Obeng, V. A., and Kresta, S. M., “Handbook of Industrial Mixing: Science and Practice”, 2004, John Wiley & Sons, Wiley Interscience, Chapter 5
Pope, S. B., “Turbulent Flows”, 2000, Cambridge University Press, Cambridge, UK, Chapter
Ranade, V. V., “Computational Flow Modeling for Chemical Reactor Engineering”, 2002, Process System Engineering Volume 5, Academic Press
Baldi, S., and Yianneskis, M., “On the Quantification of Energy Dissipation in the Impeller Stream of a Stirred Vessel from Fluctuating Velocity Gradient Measurements”, Chem. Eng. Sci., 59, pp. 2659-2671
Jones, W.P., and Launder, B.E., “The prediction of laminarization with a two-equation model”, Int. J. Heat Mass Transfer, 15, pp.304- 314
Schubert, H., 1999, “On the turbulence-controlled microprocesses in flotation machines”, Int. J. Miner. Process., 56, pp. 257-276
Fallenius, K., 1987, “Turbulence in Flotation Cells”, Int. J. Miner. Process., 21, pp. 1-23
Do, H., and Yoon, R.H., “A flotation model under turbulent flow conditions”.
Downloads
Published
How to Cite
Issue
Section
License
Copyright (c) 2013 The Research Publication
This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.
