Document Type : Research note


1 bYoung Researchers and Elite Club, Ayatollah Amoli Branch, Islamic Azad University, Amol, Iran.

2 Young Researchers and Elite Club, Ayatollah Amoli Branch, Islamic Azad University, Amol, Iran.


Computational fluid dynamics (CFD) is a powerful numerical tool that is becoming widely used to simulate many processes in the industry. In this work study of the stirred tank with 7 types of concave blade with CFD was presented. In the modeling of the impeller rotation, sliding mesh (SM) technique was used and RNG-k-ε model was selected for turbulence. Power consumption in various speeds in the single phase, mean tangential, radial and axial velocities in various points, effects of disc diameter and thickness and mixing time were investigated. The optimum concave impeller was selected and the effect of tracer feed position and probe location was investigated on it. Results suggested that power consumption is exactly depending on impellers scale and geometry, was in a good agreement with the experimental data and in turbulent flow is relatively independent of Reynolds number. Power number increases with increasing disc diameter for both concave and Rushton and concave´s power is relatively independent on disc thickness but increasing it decreases Rushton´s power. The data revealed that the power number was 2.3±0.3 for blade angle 40° whereas for blade 25°, 50° and 55° respectively 43% lower and 57% and 43% higher.


Main Subjects

[1]      Ranade, V. V., Bourne, J. R. and Joshi, J. B., “Fluid mechanics and blending in agitated tanks”, Chem. Eng. Sci., 46 (8), 1883 (1991).
[2]      Ng, K., Fentiman, N. J., Lee, K. C. and Yianneskis, M., “Assessment of sliding mesh CFD predictions and LDA measurements of  the flow in a tank stirred by a Rushton impeller”, Trans. IChemE., Part A, 76 (6), 737 (1998).
[3]      Van’t Riet, K. and Smith, J. M., “The behaviours of gas-liquid mixtures near Rushton turbine blades”, Chem. Eng.Sci., 28 (4), 1031 (1973).
[4]      Van’t Riet, K. and Smith, J. M., “The trailing vortex system produced by Rushton turbine agitators”, Chem. Eng.Sci., 30 (9), 1093 (1975).
[5]      Van’t Riet, K., Boom, J .M. and Smith, J. M, “Power consumption, impeller coalescence and rescirculation in aerated vessels”, Trans. IChemE., 54 (1), 124 (1976).
[6]      Wong, C. W. and Huang, C. T., “Flow characteristics and mechanical efficiency in baffled stirred tanks with turbine impellers”, Proceedings of The 6th European Conference on Mixing, Pavia, Italy, BHRA, Cranfield, U.K, pp. 29-34 (1988).
[7]      Wamoeskerken, M. M. C. G. and Smith, J. M., “The hollow blade agitator for dispersion and mass transfer”, Trans. IChemE., Chem. Eng. Res. Des., 67 (2), 193 (1989).
[8]      Hjorth, S., US Pat. 4779990, Imeller Apparatus., (1998).
[9]      Middleton, J. C, US Pat. 5198156, Agitators., (1993).
[10]  Galindo, E. and Nienow, A. W., “Performance of the Scaba 6SRGT agitator in mixing of simulated xanthan gum broths”, Chem. Eng. Technol., 16 (2), 102 (1993).
[11]  Bakker, A., Myers, K. J. and Smith, J. M., “How to disperse gases in liquids”, Chem. Eng., 101 (12), 98 (1994).
[12]  Nienow, A. W., “Gas–liquid mixing studies: A comparison of Rushton turbines with some modern impellers”, Chem. Eng. Res. Des., 74 (4), 417 (1996).
[13]  Bakker, A., US Pat. 5791780, Impeller Assembly with Asymmetric Concave Blades, (1998).
[14]  Pinlli, D., Bakker, A., Myers, K. J., Reeder, M. F., Fasano, J., and Magelli, F., “Some features of a novel gas dispersion impeller in a dual impeller configuration”, Trans. IChemE., 81 (4), 728 (2003).
[15]  Vlaev, S. D., Staykov, P. and Popov, R., “Pressure distribution at impeller blades of some radial flow impellers in saccharose and xanthan gum solutions a CFD visualization approach”, Trans. IChemE., Part C, 82 (1), 13 (2004).
[16]  Xinhong, L., Yuyun, B., Zhipeng, L. and Zhengming, G., “Analysis of turbulence structure in the stirred tank with a deep hollow blade disc turbine by time-resolved PIV”, Chinese Journal of Chem. Eng., 18 (4), 588 (2010).
[17]  Jing, Z. H. A. O, Zhengming, G. A. O. and Yuyun, B. A. O., “Effects of the blade shape on the trailing vortices in liquid flow generated by disc turbines”, Chinese Journal of Chem. Eng., 19 (2), 232 (2011).
[18]  Afshar Ghotli, R., Abdul Aziz, A. R., Ibrahim, Sh., Baroutian,S. and Arami-Niya, A., “Study of various curved-blade impeller geometries on power consumption in stirred vessel using response surface methodology”, Journal of the Taiwan Institute of Chemical Engineers, 44 (2), 192 (2013).
[19]  Ameur, H., “Mixing of shear thinning fluids in cylindrical tanks: Effect of the impeller blade design and operating conditions”, International Journal of Chemical Reactor Engineering, 14 (5), 1025 (2016).
[20]  Wu, H., Patterson, G. K., “Laser-doppler measurements of turblent-flow parameters in a stirrred mixer”, Chemical Engineering Science, 44 (10), 2207 (1989).
[21]  Xuereb, C., and Bertrand, J., “3-D hydrodynamics in a tank stirred by a double-propeller system and filled with a liquid having evolving rheological properties”, Chemical Engineering Science, 51 (10), 1725 (1996).
[22]  Zadghaffari, R., Moghaddas, J. S. and Revstedt, J., “A mixing study in a double-Rushton stirred tank”, Comput. Chem. Eng., 33 (7), 1240 (2009a).
[23]  Zadghaffari, R., Moghaddas, J. S. and Revstedt, J., “Study of flow field, power and mixing time in a two phase stirred vessel with dual Rushton impellers: experimental observation and CFD simulation”, Chem. Product Process. Model., 4 (1), 1 (2009b).
[24]   Shekhar, S. M and Jayanti, S., “CFD study of power and mixing time for paddle mixing in unbaffled vessels”, Trans. IChem. E., 80 (6), 482 (2002).
[25]  Paul, E. L. V. A., Atiemo, O. and Kresta, S. M., Handbook of indstrial mixing: science and practice, 3rd ed., New Jersey, John Wiley & Sons, p.145 (2004).
[26]  Brucato, A., Ciofalo, M., Grisafi, F. and Micale, G., “Numerical prediction of flows in baffled stirred vessels: A comparison of alternative modelling approaches”, Chemical Engineering Science, 53 (21), 3653 (1998).
[27]  Myers, K. J., Thomas, A. J., Bakker, A. and Reeder, M. F., “Performance of a gas dispersion impeller with vertically asymmetric blades”, Trans IChemE., 77 (8), 728 (1999).
[28]  Yapici, K., Karasozen, B., Schafer, M. and Uludag,Y., “Numerical investigation of the effect of the Rushton type turbine design factors on agitated tank flow characteristics”, Chemical Engineering and Processing, 47 (8), 1340 (2008).
[29]  Zadghaffari, R., Moghaddas, J. S. and Revstedt, J., “Large-eddy simulation of turbulent flow in a stirred tank driven by a Rushton turbine”, Comput. & Fluid, 39 (7), 1183 (2010).