Department of Chemical and Petroleum Engineering, Sharif University of Technology, I.R. IRAN
Multiphase impeller stirred tank reactors enhance mixing of reacting species used in a variety of chemical industries. These reactors have been studied based on Computational Fluid Dynamics (CFD) that can be used in the analysis, design and scale up of these reactors. Most of the researches done in this area are limited to single phase reactors, and a few remaining two phase flow investigations have been done based on MRF (Multi Reference Frame) and Snapshot approach. However, the MRF and snapshot approaches cannot be used in rigorous simulation of unsteady state problems. In order to simulate the unsteady state behavior of the multiphase stirred tank reactors we have used sliding mesh technique to solve the problem rigorously. In this work a 3D CFD model is used to investigate hydrodynamics of a fully baffled cylindrical stirred tank containing air-water in which air is sparged. The tank is equipped with a standard Rushton turbine impeller. This work has been done based on two fluid (Eulerian-Eulerian) model and finite volume method, along with standard k-e model to address turbulent behavior of both phases. The results obtained for velocity field show a good agreement with the corresponding data published by researchers in this field for the same case. The effect of gas inlet velocity on the gas holds up distribution has been studied. According to the obtained results, there should be an optimum value for gas inlet velocity in order to achieve appropriate gas distribution in the liquid. The most important parameter affecting the optimum value is impeller rotational speed.
 Harnby, N., Edwards, N.F., Nienow, A.W., “Mixing in Process Industries”, McGraw-Hill (1985).
Tatterson, G.B., “Fluid Mixing and Gas Dispersion in Agitated Tanks”, McGraw-Hill, New York (1991).
 Aubin, J., Fletcher, D.F., Xuereb, C., Modeling Turbulent Flow in Stirred Tanks with CFD: The Influence of Modeling Approach, Turbulence Model and Numerical Scheme, Experimental Thermal and Fluid Science, 28, 431 (2004).
 Bujalski, W., Jaworski, Z., Nienow, A.W., CFD Study of Homogenization with Dual Rushton Turbines-Comparision with Experimental Results-part II: The Multiple Reference Frame, Transactions of the Institution of Chemical Engineers, 80, 97 (2002).
 Jaworski, Z., Dyster, K. N., Nienow, A. W., The Effect of Size, Location and Pumping Direction of Pitched Blade Turbine Impellers on Flow Patterns: LDA Measurements and CFD Predictions, Trans-actions of the Institution of Chemical Engineers, 79, 887 (2001).
 Mavros, P., Mann, R., Vlaev, S.D., Bertrand. J., Experimental Visualization and CFD Simulation of Flow Ptterns Induced by a Novel Energy-Saving Dual-Configuration Impeller in Stirred Vessels, Transactions of the Institution of Chemical Engineers, 79, 857 (2001).
 Micale, G., Brucato, A., Grisafi, F., Ciofalo, M., Prediction of Flow Fields in Dual-Impeller Stirred Vessel, A.I.Ch.E. Journal, 45, 445 (1999).
 Murthy Shekhar, S., Jayanti, S., CFD Study of Power and Mixing Time for Paddle Mixing in Unbaffled Vessels, Transactions of the Institution of Chemical Engineers, 80, 482 (2002).
 Ng., K., Fentiman, N.J., Lee, K.C., Yianneskis, M., Assessment of Sliding Mesh CFD Predictions and LDA Measurements of the Flow in a Tank Stirred by a Rushton Impeller, Transactions of the Institution of Chemical Engineers, 76, 737 (1998).
 Bakker, A., Hydrodynamics of Stirred Gas-Liquid Dispersions, Ph.D. Thesis, Delf University of Technology, Netherlands (1992).
 Bakker, A., van der Akker, H.E.A., A Computational Model for the Gas-Liquid Flow in Stirred Reactors, Transactions of the Institution of Chemical Engineers, 72, 594 (1994).
 Djebbar, R., Roustan, M., Line, A., Numerical Computation of Gas-Liquid Dispersion in Mechanically Agitated Vessels, Transactions of the Institution of Chemical Engineers, 74, 492 (1996).
 Morud, K.E., Hjertager, B.H., LDA Measurements and CFD Modeling of Gas-liquid Flow in Stirred Vessel, Chemical Engineering Science, 51, 233 (1996).
 Ranade, V.V., Deshpande, V.R., Gas-Liquid Flow in Stirred Reactors: Trailing Vortices and Gas Accumulation Behind Impeller Blades, Chemical Engineering Science, 54, 2305 (1999).
 Deen, N. G., Solberg, T., Hjertager, B. H., Flow Generated by an Aerated Rushton Impeller: Two Phase PIV Experiments and Numerical Simulations, The Canadian Journal of Chemical Engineering, 80, 1 (2002).
 Khopkar, A.R., Aubin J., Xureb, C., Le Sauze, N., Ertrand, J., Ranade, V.V., Gas-Liquid Flow Generated by a Pitch Blade Turbine: PIV Measu-rements and CFD Simulations, Industrial and Eng-ineering Chemistry and Research, 42, 5318 (2003).
 Khophkar, A. R, Rammohan, A. R., Ranade, V. V., Dudukovic, M.P., Gas-Liquid Flow Generated by a Rushton Turbine in Stirred Tank Vessel: CAPRT/CT Measurements and CFD Simulations, Chemical Engineering Science, 60, 2215 (2005).
 Honkanen, M., Koohestani, A. , Hatunen, T., Saarenrinne, P., Zamankhan, P., Large Eddy Simulation and PIV Experiments of a Two Phase Air-Water Mixer, ASME Fluid Engineering Summer Conference, June,19-23, Houston ( 2005).
 Ranade, V. V, Computational Flow Modeling for Chemical Reactor Engineering, Academic Press, New York (2002).
 Versteeg, H. K., Malalasekera, W., An Introduction to Computational Fluid Dynamics, Addison Wesley Longman Limited, New York (1996).
 Gentric, C, Mignon, D., Bousquet, J., Tanguy, P.A., Comparison of Mixing in Two Industrial Gas-Liquid Reactors Using CFD Simulations, Chemical Engineering Science, 60, 2253 (2004).
 Buwa, V. V., Ranade, V. V., Dynamics of Gas-Liquid Flow in Rectangular Bubble Columns, Chemical Engineering Science, 57, 4715 (2002).
 Rafique, M., Chen, P., Dudokovic, M.P., Compu-tational Modeling of Gas-Liquid Flow in Bubble Columns, Reviews in Chemical Engineering, 20, 225 (2004).
 Barigou, M., Greaves, M., Buuble Size Distribution in a Mechanically Agitated Gas-Liquid Contactor, Chemical Engineering Science, 47, 2009 (1992).
 Gosman, A.D., Lekakou, C., Politis, S., Issa, R.I., Looney, M.K., Multi-dimensional Modeling of Turbulent Two Phase Flow in Stirred Vessels, A.I.Ch.E. Journal, 38, 1947 (1992).
 Luo, J. Y., Gosman, A. D., Prediction of Impeller-Induced Flow in Mixing Vessels Using Multiple Frames of Reference, Institution of Chemical Engineering Symposium Series, 136, 549 (1994).
 Brucato, A., Ciofalo, M., Grisafi, F., Micale, G., Complete Numerical Simulation of Flow Fields in Baffled Stirred Vessels: The Inner-Outer Approach, Institution of Chemical Engineering Symposium Series, 1360, 155 (1994).
 Ranade, V.V., van den Akker, H.E.A., A Compu-tational Snapshot of Gas-Liquid Flow in Baffled Stirred Reactors, Chemical Engineering Science, 49, 5175 (1994).
 Luo, J.Y., Gosman, A.D., Issa, R.I., Midelton, J.C. and Fitzgerald, M.K., Full Flow Field Computation of Mixing in Bafeled Stirred Vessels, Chemical EngineeringReserch and Design, 71(A), 342 (1993).
 Montante, G., Lee, K.C., Brucato, A., Yianneskis, M., Numerical Simulations of the Dependency of Flow Pattern on Impeller Clearance in Stirred Vessel, Chemical Engineering Science, 56, 3351 (2001).
 Ciofalo, M., Brucato, A., Grisafi, F., Tocco, R., Turbulent Flow in Closed and Free-Surface Tanks Stirred by Radial Impeller, Chemical Engineering Science, 51, 3557 (1996).
 Brucato, A., Ciofalo, M., Grisafi, F., Tocco, R., On the Simulation of Stirred Tank Reactors Via Computational Fluid Dynamics, Chemical Engineering Science, 55, 291 (2002).