Commenced in January 2007
Paper Count: 30124
The Effect of Bottom Shape and Baffle Length on the Flow Field in Stirred Tanks in Turbulent and Transitional Flow
Abstract:The effect of the shape of the vessel bottom and the length of baffles on the velocity distributions in a turbulent and in a transitional flow has been simulated. The turbulent flow was simulated using standard k-ε model and simulation was verified using LES whereas transitional flow was simulated using only LES. It has been found that both the shape of tank bottom and the baffles’ length has significant effect on the flow pattern and velocity distribution below the impeller. In the dished bottom tank with baffles reaching the edge of the dish, the large rotating volume of liquid was formed below the impeller. Liquid in this rotating region was not fully mixing. A dead zone was formed here. The size and the intensity of circulation within this zone calculated by k-ε model and LES were practically identical what reinforces the accuracy of the numerical simulations. Both types of simulations also show that employing full-length baffles can reduce the size of dead zone formed below the impeller. The LES was also used to simulate the velocity distribution below the impeller in transitional flow and it has been found that secondary circulation loops were formed near the tank bottom in all investigated geometries. However, in this case the length of baffles has smaller effect on the volume of rotating liquid than in the turbulent flow.
Digital Object Identifier (DOI): doi.org/10.5281/zenodo.1126537Procedia APA BibTeX Chicago EndNote Harvard JSON MLA RIS XML ISO 690 PDF Downloads 1405
 Paul, E.L., V.A. Atiemo-Obeng, and S.M. Kresta, Handbook of industrial mixing science and practice. 2004, John Wiley & Sons, Inc.: Canada.
 Smith, J.M., Industrial needs for mixing research. chemical Engineering Research and Design, 1990. 68.
 Bakker, A. and H.E.A. Van den Akker, Single-phase flow in stirred reactors. Chemical Engineering Research and Design, 1994. 72(A4): p. 583-593.
 Ng, K. and M. Yianneskis, Observations on the distribution of energy dissipation in stirred vessels. Chemical Engineering Research and Design, 2000. 78(3): p. 334-341.
 Kumaresan, T. and J.B. Joshi, Effect of impeller design on the flow pattern and mixing in stirred tanks. Chemical Engineering Journal, 2006. 115(3): p. 173-193.
 Bakker, A. and H.E.A. Van den Akker, Gas-liquid contacting with axial flow impellers. Chemical Engineering Research and Design, 1994. 72(A4): p. 573-582.
 Gimbun, J., C.D. Rielly, and Z.K. Nagy, Modelling of mass transfer in gas–liquid stirred tanks agitated by Rushton turbine and CD-6 impeller: A scale-up study. Chemical Engineering Research and Design, 2009. 87(4): p. 437-451.
 Joshi, J.B., et al., CFD Simulation of stirred tanks: comparison of turbulence models. part i: radial flow impellers. Canadian Journal of Chemical Engineering, 2011. 89(1): p. 23-82.
 Joshi, J.B., et al., CFD simulation of stirred tanks: comparison of turbulence models (part ii: axial flow impellers, multiple impellers and multiphase dispersions). Canadian Journal of Chemical Engineering, 2011. 89(4): p. 754-816.
 Bakker, A. and L.M. Oshinowo, Modelling of turbulence in stirred vessels using large eddy simulation. Chemical Engineering Research and Design, 2004. 82(9): p. 1169-1178.
 Derksen, J. and H.E.A. Van den Akker, Large eddy simulations on the flow driven by a Rushton turbine. AIChE Journal, 1999. 45(2): p. 209-221.
 Eggels, J.G.M., Direct and large-eddy simulation of turbulent fluid flow using the Lattice-Boltzmann scheme. International Journal of Heat and Fluid Flow, 1996. 17(3): p. 307-323.
 Deglon, D.A. and C.J. Meyer, CFD modelling of stirred tanks: Numerical considerations. Minerals Engineering, 2006. 19(10): p. 1059-1068.
 Aubin, J., D.F. Fletcher, and C. Xuereb, Modeling turbulent flow in stirred tanks with CFD: The influence of the modeling approach, turbulence model and numerical scheme. Experimental Thermal and Fluid Science, 2004. 28(5): p. 431-445.
 Wu, H. and G.K. Patterson, Laser-Doppler measurements of turbulent-flow parameters in a stirred mixer. Chemical Engineering Science, 1989. 44(10): p. 2207-2221.
 Roy, S., S. Acharya, and M.D. Cloeter, Flow structure and the effect of macro-instabilities in a pitched-blade stirred tank. Chemical Engineering Science, 2010. 65(10): p. 3009-3024.
 Deen, N.G., T. Solberg, and B.H. Hjertager, Flow generated by an aerated rushton impeller: two-phase piv experiments and numerical simulations. The Canadian Journal of Chemical Engineering, 2002. 80(4): p. 1-15.
 Gabriele, A., A.W. Nienow, and M.J.H. Simmons, Use of angle resolved PIV to estimate local specific energy dissipation rates for up- and down-pumping pitched blade agitators in a stirred tank. Chemical Engineering Science, 2009. 64(1): p. 126-143.
 Jaworski, Z. and B. Zakrzewska, Modelling of the turbulent wall jet generated by a pitched blade turbine impeller: the effect of turbulence model. Chemical Engineering Research and Design, 2002. 80(8): p. 846-854.
 Ochieng, A. and M.S. Onyango, CFD simulation of solids suspension in stirred tanks: review. Hemijska Industrija, 2010. 64(5): p. 365-374.
 Lu, W.-M., H.-Z. Wu, and M.-Y. Ju, Effects of baffle design on the liquid mixing in an aerated stirred tank with standard Rushton turbine impellers. Chemical Engineering Science, 1997. 52(21–22): p. 3843-3851.
 Karcz, J. and M. Major, An effect of a baffle length on the power consumption in an agitated vessel. Chemical Engineering and Processing: Process Intensification, 1998. 37(3): p. 249-256.
 Haque, J.N., et al., Free-surface turbulent flow induced by a Rushton turbine in an unbaffled dish-bottom stirred tank reactor: LDV measurements and CFD simulations. The Canadian Journal of Chemical Engineering, 2011. 89(4): p. 745-753.
 Jaworski, Z., et al., Sliding mesh simulation of transitional, non-newtonian flow in a baffled stirred tank, in Computation of Three-Dimensional Complex Flows, M. Deville, S. Gavrilakis, and I. Ryhming, Editors. 1996, Vieweg+Teubner Verlag. p. 109-115.
 Yang, F., et al., Mixing of initially stratified miscible fluids in an eccentric stirred tank: Detached eddy simulation and volume of fluid study. Korean Journal of Chemical Engineering, 2013. 30(10): p. 1843-1854.
 Woziwodzki, S., L. Broniarz-Press, and M. Ochowiak, Effect of eccentricity on transitional mixing in vessel equipped with turbine impellers. Chemical Engineering Research and Design, 2010. 88(12): p. 1607-1614.
 Versteeg, H.K. and W. Malalasekera, An introduction to computational fluid dynamics the finite volume method. 2007, Pearson Education Ltd.
 ANSYS, ANSYS FLUENT theory guide. Pennsylvania: ANSYS Ltd. 2011.
 Hartmann, H., et al., Assessment of large eddy and RANS stirred tank simulations by means of LDA. Chemical Engineering Science, 2004. 59(12): p. 2419-2432.
 Fan, J., Y. Wang, and W. Fei, Large eddy simulations of flow instabilities in a stirred tank generated by a Rushton turbine. Chinese Journal of Chemical Engineering, 2007. 15(2): p. 200-208.
 Zadghaffari, R., J.S. Moghaddas, and J. Revstedt, Large-eddy simulation of turbulent flow in a stirred tank driven by a Rushton turbine. Computers & Fluids, 2010. 39(7): p. 1183-1190.
 Delafosse, A., et al., LES and URANS simulations of hydrodynamics in mixing tank: Comparison to PIV experiments. Chemical Engineering Research and Design, 2008. 86(12): p. 1322-1330.
 SHAW, C.T., Using computational fluid dynamics. 1992, New York: Prentice Hall.
 Busciglio, A., G. Caputo, and F. Scargiali, Free-surface shape in unbaffled stirred vessels: Experimental study via digital image analysis. Chemical Engineering Science, 2013. 104(0): p. 868-880.
 Lamarque, N., et al., Large-eddy simulation of the turbulent free-surface flow in an unbaffled stirred tank reactor. Chemical Engineering Science, 2010. 65(15): p. 4307-4322.
 Murthy Shekhar, S. and S. Jayanti, CFD study of power and mixing time for paddle mixing in unbaffled vessels. Chemical Engineering Research and Design, 2002. 80(5): p. 482-498.
 Sano, Y. and H. Usui, Interrelations among mixing time, power number and discharge flow rate number in baffled mixing vessels. Journal of Chemical Engineering of Japan, 1985. 18(1): p. 47-52.
 Lamberto, D.J., M.M. Alvarez, and F.J. Muzzio, Experimental and computational investigation of the laminar flow structure in a stirred tank. Chemical Engineering Science, 1999. 54(7): p. 919-942.