Numerical Study of Vortex Formation inside a Stirred Tank

Authors: Divya Rajavathsavai, Akhilesh Khapre, Basudeb Munshi

Abstract:

The computational fluid dynamics (CFD) study of stirred tank with the air-water interface are carried out in the presence of different types of the impeller and with or without baffles. A multiple reference frame (MRF) approach with the volume of fluid (VOF) method is used to capture the air-water interface. The RANS (Reynolds Averaged Navier-Stokes) equations with k-ε turbulence model are solved to predict the flow behavior of water and air phase which are treated as a different phases. The predicted results have shown that the VOF method is able to capture the interface in the unbaffled tank. While, the VOF method is showing an unfeasible results in the baffled tank with high rotational impeller speed. For continuous stirred tank, the air-water interface is disturbed by the inflow and the level of water is also increased with time.

Keywords: Computational Fluid Dynamics, stirred tank, airwater interface, multiple reference frame, volume of fluid, Reynolds Averaged Navier-Stokes equations.

Digital Object Identifier (DOI): doi.org/10.5281/zenodo.1337895

References:

[1] T. Mahmud, J. N. Haque, K. J. Roberts, D. Rhodes and D. Wilkinson, "Measurements and modelling of free-surface turbulent flows induced by a magnetic stirrer in an unbaffled stirred tank reactor", Chemical Engineering Science, vol. 64, pp. 4197–4209, 2009.
[2] S. Nagata, Mixing Principles and Applications, Wiley, New York, 1975.
[3] M. Ciofalo, A. Brucato, F. Grisafi and N. Torraca, “Turbulent flow in closed and free-surface unbaffled tanks stirred by radial impeller”, Chemical Engineering Science, Vol. 51, pp. 3557–3573, 1996.
[4] A. Serra, M. Campolo and A. Soldati, “Time dependent finite-volume simulation of the turbulent flow in a free-surface CSTR”, Chemical Engineering Science, Vol. 56, pp. 2715–2720, 2001.
[5] J. N. Haque, T. Mahmud, K. J. Roberts and D. Rhodes, “Modeling turbulent flows with free-surface in unbaffled agitated vessels”, Industrial and Engineering Chemistry Research, Vol. 45, pp. 2881– 2891, 2006
[6] J. Torré, D. F. Fletcher, T. Lasuye and C. Xuereb, “Single and multiphase CFD approaches for modelling partial baffled stirred vessels: Comparison of experimental data with numerical predictions”, Chemical Engineering science, Vol. 62, pp. 6246–6262, 2007
[7] N. Lamarque, B. Zoppe, O. Lebaigue, Y. Dolias, M. Bertrand and F. Ducros, “Large-eddy simulation of the turbulent free-surface flow in an unbaffled stirred tank reactor”, Chemical Engineering Science, Vol. 65, pp. 4307–4322, 2010.
[8] M. Zlokarnik, “Trombentiefebeimrühren in unbewehrtenbehältern”, ChemieIngenieurTechnik, Vol. 43, pp.1028–1030, 1971.
[9] ANSYS FLUENT 12.0 Theory Guide, Chapter 16: Multiphase Flow, ANSYS, Inc., 2009.