CFD Study of the Fluid Viscosity Variation and Effect on the Flow in a Stirred Tank

Authors: Achouri Ryma, Hatem Dhaouadi, Hatem Mhiri, Philippe Bournot

Abstract:

Stirred tanks are widely used in all industrial sectors. The need for further studies of the mixing operation and its different aspects comes from the diversity of agitation tools and implemented geometries in addition to the specific characteristics of each application. Viscous fluids are often encountered in industry and they represent the majority of treated cases, as in the polymer sector, food processing, pharmaceuticals and cosmetics. That's why in this paper, we will present a three-dimensional numerical study using the software Fluent, to study the effect of varying the fluid viscosity in a stirred tank with a Rushton turbine. This viscosity variation was performed by adding carboxymethylcellulose (CMC) to the fluid (water) in the vessel. In this work, we studied first the flow generated in the tank with a Rushton turbine. Second, we studied the effect of the fluid viscosity variation on the thermodynamic quantities defining the flow. For this, three viscosities (0.9% CMC, 1.1% CMC and 1.7% CMC) were considered.

Keywords: CFD, CMC, Mixing, Viscosity, Rushton turbine.

Digital Object Identifier (DOI): doi.org/10.5281/zenodo.1336114

References:

[1] C. Gómez, C. P. J. Bennington, and F. Taghipour. Investigation of the Flow Field in a Rectangular Vessel Equipped With a Side-Entering Agitator. J. Fluids Eng. , 2010. 132, 051106.
[2] Si Y. Lee and Richard A. Dimenna. Applications of CFD Method to Gas Mixing Analysis in a Large-Scaled Tank. ASME Conf. Proc., 2007. FEDSM2007.
[3] Robert A. Leishear, Si Y. Lee, Mark D. Fowley, Michael R. Poirier, and Timothy J. Steeper. Comparison of Experiments to Computational Fluid Dynamics Models for Mixing Using Dual Opposing Jets in Tanks With and Without Internal Obstructions. J. Fluids Eng. , 2012. 134, 111102.
[4] Paul A. Gillis, Gerrit Hommersom, and Matthias Schäfer. A Comparison of Several CFD Approaches for Predicting Gas-Liquid Contacting in a Cylindrical Tank Agitated With a Single Rushton Turbine. ASME Conf. Proc., 2002. PVP2002.
[5] Ranade, V.V.. An efficient computational model for simulating flow in stirred vessels: case of Rushton turbine. Chem Eng Sci, , 1997. Vol. 52, 24, 4473–4484.
[6] NG, K. et al. Assessment of sliding mesh CFD predictions and LDA measurements of the flow in a tank stirred by a Rushton impeller. TransI Chem E., 1998. Vol. 76, partA, 737-747.
[7] Kumaresan, T et al. Effect of impeller design on the flow pattern and mixing in stirred tanks. Chem Eng Sci,, 2006. 115.
[8] Mavors, P.. Flow visualization in stirred vessels-A review of experimental techniques. TransI ChemE., 2001. Vol. 79, part A, 113-127.
[9] Zadghaffari, R. et al. Large Eddy Simulation of turbulent flow in a stirred tank driven by a Rushton turbine. Computer & Fluids, 2010. Volume 39, Issue 7, 1183–1190.
[10] Lu, W. et Yang, B.. Effect of blade on the structure of the trailing vortex around Rushton turbine impellers. Can. J. Chem. Eng., 1998. Vol. 76, 556–562.
[11] Ochieng,A. et al. Mixing in a tank stirred by a rushton turbine at a low clearance. Chem. Eng. Process, 2008. Vol. 47, 842-851.
[12] Brucato, A et al. Numerical prediction of flow fields in baffled stirred vessels: A comparison of alternative modeling approches. Chem Eng Sci, , 1998. Vol. 53, 21.
[13] NG, K. et Yianneskis, M.. Obsevations on the distribution of energy dissipation in stirred vessels. TransI ChemE,, 2000. Vol. 78, part A, 334-341.
[14] Mavros, P et al. Determination of flow fields in agitated vessels by Laser-Doppler Velocimetry: Use and interpretation of RMS velocities. Trans IChemE,, 1998. Vol. 76, part A, 223-233.
[15] Yundong, W. et al. PIV measurements and CFD simulation of viscous fluid flow in a stirred tank agitated by a Rushton turbine. Melbourne, Australia: CSIRO, Fifth International Conference on CFD in the Process Industries, 2006.
[16] Triveni, B. et al. Mixing studies of non newtonian fluids in an anchor agitated vessel. Chem. Eng. Res. Des.,, 2010. Vol. 88, 809-818.