|  N. Harnby, M.F. Edwards, A.W. Nienow, Mixing in the Process Industries, Butterworth-Heinemann, Oxford, UK, 1997. G.K. Patterson, E.L. Paul, S.M. Kresta, A.W. Etchells III,Mixing and chemical reactions, in: E.M. Paul, S.M. Kresta, V.A. Atiemo-Obeng (Eds.), Handbook of IndustrialMixing: Science and Practice, JohnWiley & Sons, New Jersey, 2004. G.B. Tatterson, Fluid Mixing and Gas Dispersion in Agitated Tanks, McGraw-Hill, USA, 1991. M.Moo-Young, K. Tichar, F.A.L. Dullien, The blending efficiencies of some impellers in batch mixing, AIChE J. 18 (1972) 178-182. A.B. Metzner, R.E. Otto, Agitation of non-Newtonian fluids, AIChE J. 3 (1957) 3-10. S. Nagata, Mixing: Principles and Applications, Wiley, New York, 1975. M. Nishikawa, K. Ashiwake, N. Hashimoto, S. Nagata, Agitation power and mixing time in off-centering mixing, Int. Chem. Eng. 19 (1979) 153-159. N.K. Nere, A.W. Patwardhan, J.B. Joshi, Liquid-phase mixing in stirred vessels: turbulent flow regime, Ind. Eng. Chem. Res. 42 (2003) 2661-2698. Y. Sano, H. Usui, Effects of paddle dimensions and baffle conditions on the interrelations among discharge flow rate, mixing power and mixing time in mixing vessels, J. Chem. Eng. Jpn. 20 (1987) 399-404. R.K. Grenville, A.W. Nienow, Blending of miscible liquids, in: E.M. Paul, S.M. Kresta, V.A. Atiemo-Obeng (Eds.), Handbook of IndustrialMixing: Science and Practice, 1st ed.John Wiley, New Jersey, 2004. J. Szoplik, J. Karcz, An efficiency of the liquid homogenization in agitated vessels equipped with off-centred impellers, Chem. Pap. 59 (2005) 373-379. P. Mavros, Flow visualization in stirred vessels. A review of experimental techniques, Chem. Eng. Res. Des. 79 (2001) 113-127. C.J. Hoogendoorn, A.P. den Hartog, Model studies on mixers in the viscous flow region, Chem. Eng. Sci. 22 (1967) 1689-1699. P.J. Carreau, I. Patterson, C.Y. Yap, Mixing of viscoelastic fluids with helical-ribbon agitators. I — mixing time and flow patterns, Can. J. Chem. Eng. 54 (1976) 135-142. M. Kraume, P. Zehner, Experience with experimental standards for measurements of various parameters in stirred tanks: a comparative test, Chem. Eng. Res. Des. 79 (2001) 811-818. D.J. Lamberto, F.J. Muzzio, P.D. Swanson, A.L. Tonkovich, Using time-dependent RPM to enhance mixing in stirred vessels, Chem. Eng. Sci. 51 (1996) 733-741. W.G. Yao, H. Sato, K. Takahashi, K. Koyama, Mixing performance experiments in impeller stirred tanks subjected to unsteady rotational speeds, Chem. Eng. Sci. 53 (1998) 3031-3040. G. Ascanio, M. Brito-Bazán, E. Brito-de la Fuente, P.J. Carreau, P.A. Tanguy, Unconventional configuration studies to improve mixing times in stirred tanks, Can. J. Chem. Eng. 80 (2002) 558-565. M. Alvarez, P.E. Arratia, F.J. Muzzio, Laminar mixing in eccentric stirred tank systems, Can. J. Chem. Eng. 80 (2002) 546-557. G. Ascanio, S. Foucault, P.A. Tanguy, Time-periodic mixing of shear-thinning fluids, Chem. Eng. Res. Des. 82 (2004) 1199-1203. A. Hidalgo-Millán, Geometric perturbations in mechanically agitated tanks(Ph.D. dissertation) National Autonomous University of Mexico, 2010. (in Spanish). K.W. Norwood, A.B. Metzner, Flow patterns and mixing rates in agitated vessels, AIChE J 6 (1960) 432-437. D. Hari-Prajitno, V.P. Mishra, K. Takenaka, W. Bujalski, A.W. Nienow, J. Mckemmie, Gas-liquid mixing studies with multiple up-and down-pumping hydrofoil impellers: power characteristics and mixing time, Can. J. Chem. Eng. 76 (1998) 1056-1068. A.B. Pandit, C.D. Rielly, K. Niranjan, J.F. Davidson, The convex bladed mixed flow impeller and the marine propeller: A multipurpose agitator, Chem. Eng. Sci. 44 (1989) 2463-2474. S.-J. Wang, J.-J. Zhong, A novel centrifugal impeller bioreactor. I. Fluid circulation, mixing, and liquid velocity profiles, Biotechnol. Bioeng. 51 (1996) 511-519. T. Espinosa-Solares, E. Brito-de la Fuente, A. Tecante, L.Medina-Torres, P.A. Tanguy, Mixing time in rheologically evolving model fluids by hybrid dual mixing systems, Chem. Eng. Res. Des. 80 (2001) 817-823. S. Foucault, G. Ascanio, P.A. Tanguy,Mixing times in coaxial mixerswith Newtonian and non-Newtonian fluids, Ind. Eng. Chem. Res. 45 (2006) 352-359. Y.Hirata, R. Ito, Characteristics of flowandmixing in vesselwith rotatingmultistage disks, Ing, Proceedings of 6th European Conference on Mixing, Pavia, Italy, 1988. O. Hiruta, K. Yamamura, H. Takebe, T. Futamura, K. Iinuma,H. Tanaka, Application of Maxblend fermentor® formicrobial processes, J. Ferment. Bioeng. 83 (1997) 79-86. A. Iranshahi, C. Devals, M. Heniche, L. Fradette, P.A. Tanguy, K. Takenaka, Hydrodynamics characterization of the Maxblend impeller, Chem. Eng. Sci. 62 (2007) 3641-3653. K. Takahashi, T. Yokota, T. Furukawa, K. Harada, Mixing of highly viscous Newtonian liquid in a helical ribbon agitated vessel at various liquid depths, J. Chem. Eng. Jpn 27 (1994) 244-247. T. Takahashi, A. Tagawa,N. Atsumi, N. Dohi, Y. Kawase, Liquid-phase mixing time in boiling stirred tank reactors with large cross-section impellers, Chem. Eng. Process. 45 (2006) 303-311. K. Takahashi, Y. Sugo, Y. Takahata, H. Sekine, M. Nakamura, Laminar mixing in stirred tank agitated by an impeller inclined, Int. J. Chem. Eng. 2012 (2012).http://dx.doi.org/10.1155/2012/858329 (10 pp., Article 858329). E. Aizawa,N. Sakano,H. Imakoma,N. Ohmura, Effect of rheological property of fluids on mixing time in a stirred vessel, Kagaku Kogaku Ronbun 35 (2009) 539-542. T. Kouda, H. Yano, F. Yoshinaga, M. Kaminoyama, M. Kamiwano, Characterization of non-Newtonian behavior during mixing of bacterial cellulose in a bioreactor, J. Ferment. Bioeng. 82 (1996) 382-386. G. Delaplace, L. Bouvier, A. Moreau, R. Guérin, J.C. Leuliet, Determination of mixing time by colourimetric diagnosis — application to a new mixing system, Exp. Fluids 36 (2004) 437-443. R.P. Chhabra, L. Bouvier, G. Delaplace, G. Cuvelier, S.Domenek, C. André,Determination of mixing timeswith helical ribbon impeller for non-Newtonian viscous fluids using an advanced imaging method, Chem. Eng. Technol. 30 (2007) 1686-1691. O. Visuri, M. Laakkonen, J. Aittamaa, A digital imaging technique for the analysis of local inhomogeneities from agitated vessels, Chem. Eng. Technol. 30 (2007) 1692-1699. F. Cabaret, S. Bonnot, L. Fradette, P.A. Tanguy,Mixing time analysis using colorimetric methods and image processing, Ind. Eng. Chem. Res. 46 (2007) 5032-5042. L. Vega-Alvarado, B. Taboada, A. Hidalgo-Millán, G. Ascanio, Image analysismethod for the measurement of mixing times in stirred vessels, Chem. Eng. Technol. 34 (2011) 859-866. ITS-Industrial Tomography Systems Plc, http://www.itoms.com (visited on February 2013). H.S. Tapp, R.A. Williams, Status and applications of microelectrical resistance tomography, Chem. Eng. J. 77 (2000) 119-125. P.J. Holden, M. Wang, R. Mann, F.J. Dickin, R.B. Edwards, Imaging stirred-vessel macromixing using electrical resistance tomography, AIChE J. 44 (1998) 780-790. R. Mann, F.J. Dickin, M. Wang, T. Dyakowski, R.A. Williams, R.B. Edwards, A.E. Forrest, P.J. Holden, Application of electrical resistance tomography to interrogate mixing processes at plant scale, Chem. Eng. Sci. 52 (1997) 2087-2097. R.Mann,M.Wang,A.E. Forrest, P.J.Holden, F.J. Dyakwski,Gas-liquid and miscible liquid mixing in a plant-scale vessel monitored using electrical resistance tomography, Chem. Eng. Commun. 175 (1999) 33-48. P.J. Holden, M. Wang, R. Mann, F.J. Dickin, R.B. Edwards, On detecting mixing pathologies inside a stirred vessel using electrical resistance tomography, Chem. Eng. Res. Des. 77 (1999) 709-712. P.A.T. Pinheiro, W.W. Loh, R.C. Waterfall, M. Wang, R. Mann, Three-dimensional electrical resistance tomography in a stirred vessel, Chem. Eng. Commun. 175 (1999) 25-38. M. Wang, A. Dorward, D. Vlaev, R. Mann, Measurements of gas-liquid mixing in a stirred vessel using electrical resistance tomography (ERT), Chem. Eng. J. 77 (2000) 93-98. S.J. Stanley, R. Mann, K. Primrose, Tomographic imaging of fluid mixing in three dimensions for single-feed semi-batch operation of a stirred vessel, Chem. Eng. Res. Des. 80 (2002) 903-909. S.J. Stanley, R. Mann, K. Primrose, Interrogation of a precipitation reaction by electrical resistance tomography (ERT), AIChE J. 51 (2005) 607-614. S.J. Stanley, Tomographic imaging during reactive precipitation in a stirred vessel: mixing with chemical reaction, Chem. Eng. Sci. 61 (2006) 7850-7863. L. Pakzad, F. Ein-Mozaffari, P. Chan, Measuring mixing time in the agitation of non-Newtonian fluids through electrical resistance tomography, Chem. Eng. Technol. 31 (2008) 1838-1845. T.L. Rodgers, L. Gangolf, C. Vannier, M. Parriaud,M. Cooke,Mixing times for process vessels with aspect ratios greater than one, Chem. Eng. Sci. 66 (2011) 2935-2944. T.L. Rodgers, A.Kowalski, An electrical resistance tomographymethod for determining mixing in batch addition with a level change, Chem. Eng. Res. Des. 88 (2010) 204-212. T.L. Rodgers, M. Cooke, F.R. Siperstein, A. Kowalski, Mixing and dissolution times for a Cowles disk agitator in large-scale emulsion preparation, Ind. Eng. Chem. Res. 48 (2009) 6859-6868. T.L. Rodgers, F.R. Siperstein, R. Mann, T.A. York, A. Kowalski, Comparison of a networks-of-zones fluid mixing model for a baffled stirred vessel with threedimensional electrical resistance tomography, Meas. Sci. Technol. 22 (2011) (article 104014). L. Pakzad, F. Ein-Mozaffari, S.R. Upreti, A. Lohi, Characterisation of the mixing of non-Newtonian fluids with a Scaba 6SRGT impeller through ERT and CFD, Can. J. Chem. Eng. 91 (2013) 90-100. R. Mann, ERT imaging and linkage to CFD for stirred vessels in the chemical process industry, Proceedings of IEEE International Workshop Imaging Systems, IST 2009, Hong Kong, 2009. M. Wang, A. Dorward, D. Vlaev, R. Mann, Measurements of gas-liquid mixing in a stirred vessel using electrical resistance tomography (ERT), Proceedings of the 1st World Congress Industrial Process Tomography, Buxton, Greater Manchester, 1999. B. Abdullah, C. Dave, T.-H. Nguyen, C.G. Cooper, A.A. Adesina, Electrical resistance tomography-assisted analysis of dispersed phase hold-up in a gas-inducing mechanically stirred vessel, Chem. Eng. Sci. 66 (2011) 5648-5662. Dantec Dynamics, Inc., http://www.dantecdynamics.com (visited on February 2014). I. Edwards, S.A. Axon, M. Barigou, E.H. Stitt, Combined use of PEPT and ERT in the study of aluminum hydroxide precipitation, Ind. Eng. Chem. Res. 48 (2009) 1019-1028. PEPT Cape Town, http://www.pept.uct.ac.za/ (visited on February 2013). Y.S. Fangary, M. Barigou, J.P.K. Seville, D.J. Parker, Fluid trajectories in a stirred vessel of non-Newtonian liquid using positron emission particle tracking, Chem. Eng. Sci. 55 (2000) 5969-5979. M. Barigou, F. Chiti, P. Pianko-Oprych, A. Guida, L. Adams, X. Fan, D.J. Parker, A.W. Nienow, Using positron emission particle tracking (PEPT) to study mixing in stirred vessels: Validation and tackling unsolved problems in opaque systems, J. Chem. Eng. Jpn. 42 (2009) 839-846. W.M. Yek, M.N. Noui-Mehidi, R. Parthasarathy, S.N. Bhattacharya, J. Wu, N. Ohmura, N. Nishioka, Enhanced mixing of Newtonian fluids in a stirred vessel using impeller speed modulation, Can. J. Chem. Eng. 87 (2009) 839-846. M.F.W. Distelhoff, A.J. Marquis, J.M. Nouri, J.H. Whitelaw, Scalar mixing measurements in batch operated stirred tanks, Can. J. Chem. Eng. 75 (1997) 641-652. J.F. Hall, M. Barigou, M.J.H. Simmons, E.H. Stitt, Mixing in unbaffled highthroughput experimentation reactors, Ind. Eng. Chem. Res. 43 (2004) 4149-4158. K.H.K. Chung, M. Barigou, M.J.H. Simmons, Reconstruction of 3-D flow field inside miniature stirred vessels using a 2-D PIV technique, Chem. Eng. Res. Des. 85 (2007) 560-567. R. Zadghaffari, J.S. Moghaddas, J. Revstedt, A mixing study in a double-Rushton stirred tank, Comput. Chem. Eng. 33 (2009) 1240-1246. M.L. Collignon, D. Dossin, A. Delafosse, M. Crine, D. Toye, Quality of mixing in a stirred bioreactor for animal cells culture: heterogeneities in a lab scale bioreactor and evolution of mixing time with scale up, Biotechnol. Agron. Environ. 14 (S2) (2010) 585-591. A. Busciglio, F. Grisafi, F. Scargiali,A.Brucato,Mixingtime inunbaffled stirred tanks, Proceedings of 14th European Conference of Mixing, Warszawa, Poland, 2012. P.E. Arratia, F.J. Muzzio, Planar laser-induced fluorescence method for analysis of mixing in laminar flows, Ind. Eng. Chem. Res. 43 (2004) 6557-6568. Y. Hu, Z. Liu, J. Yang, Y. Jin, Y. Cheng, Study on the reactive mixing process in an unbaffled stirred tank using planar laser-induced fluorescence (pLIF) technique, Chem. Eng. Sci. 65 (2010) 4511-4518. Y. Hu, W. Wang, T. Shao, J. Yang, Y. Cheng, Visualization of reactive and nonreactive mixing processes in a stirred tank using planar induced fluorescence (pLIF) technique, Chem. Eng. Res. Des. 90 (2012) 524-533. I. Houcine, H. Vivier, E. Plasari, R. David, J. Villermaux, Planar laser induced fluorescence technique for measurements of concentration fields in continuous stirred tank reactors, Exp. Fluids 22 (1996) 95-102. A. Fall, O. Lecoq, R. David, Characterization of mixing in a stirred tank by planar laser induced fluorescence (P.L.I.F.), Chem. Eng. Res. Des. 79 (2001) 876-882. K.C. Lee,M. Yianneskis, J. Bertrand, J. Villermaux,Measurement of temperature and mixing time in stirred vessels with liquid crystal thermography, Proceedings of 9th European Conference on Mixing, Paris, France, 1997. K.C. Lee, M. Yianneskis, A liquid crystal thermographic technique for themeasurement of mixing characteristics in stirred vessels, Chem. Eng. Res. Des. 75 (1997) 746-754. D.A.R. Brown, P.N. Jones, J.C. Middleton, Experimental methods, part A: measuring tools and techniques for mixing and flow visualization studies, in: E.M. Paul, S.M. Kresta, V.A. Atiemo-Obeng (Eds.), Handbook of Industrial Mixing: Science and Practice, 1st ed.John Wiley & Sons, New Jersey, 2004. D.B. Holmes, R.M. Voncken, J.A. Dekker, Fluid flow in turbine-stirred, baffled tanks—I. Circulation time, Chem. Eng. Sci. 19 (1964) 201-208. I. Bouwmans, A. Barker, H.E.A. van Den Akker, Blending liquids of differing viscosities and densities in stirred vessels, Chem. Eng. Res. Des. 75 (1997) 777-783. M. Giona, A. Paglianti, S. Cerbelli, S. Pintus, A. Adrover, Tracer dispersion in stirred tank reactors: asymptotic properties andmixing characterization, Can. J. Chem. Eng. 80 (2002) 580-590. Y. Sano, H. Usui, Interrelations among mixing time, power number and discharge flow rate number baffled mixing vessels, J. Chem. Eng. Jpn. 18 (1985) 47-52. M. Jahoda, V. Machon, Homogenization of liquids in tanks stirred by multiple impellers, Chem. Eng. Technol. 17 (1994) 95-101. K. Rutherford, K.C. Lee, S.M.S. Mahmoudi, M. Yianneskis, Hydrodynamic characteristics of dual Rushton impeller stirred vessels, AIChE J. 42 (1996) 332-346. J.-U. Becker, F. Oeters,Model experiments ofmixing in steel ladles with continuous addition of the substance to be mixed, Steel Res. Int. 69 (1998) 8-16. P.R. Gogate, A.B. Pandit, Mixing of miscible liquids with density differences: effect of volume and density of the tracer fluid, Can. J. Chem. Eng. 77 (1999) 988-996. N. Kamei, S. Hiraoka, Y. Kato, Y. Tada, K. Yamazaki, Effects of impeller and baffle conditions on mixing time in turbulent agitated vessels, Kagaku Kogaku Ronbun 28 (2002) 9-15. M. Michelett, L. Nikiforaki, K.C. Lee, M. Yianneskis, Particle concentration and mixing characteristics of moderate-to-dense solid-liquid suspensions, Ind. Eng. Chem. Res. 42 (2003) 6236-6249. G.R. Kasat, A.B. Pandit, Mixing time studies in multiple impeller agitated reactors, Can. J. Chem. Eng. 82 (2004) 892-904. J. Mandal, S. Patil, M. Madan, D. Mazumdar, Mixing time and correlation for ladles stirred with dual porous plugs, Metall. Mater. Trans. B 36 (2005) 479-487. F. Delvigne, J. Destain, P. Thonart, Structured mixing model for stirred bioreactors: an extension to the stochastic approach, Chem. Eng. J. 113 (2005) 1-12. A.H.G. Cents, D.J.W. Jansen, D.W.F. Brilman, G.F. Versteeg, Influence of small amounts of additives on gas hold-up, bubble size, and interfacial area, Ind. Eng. Chem. Res. 44 (2005) 4863-4870. T. Kumaresan, N.K. Nere, J.B. Joshi, Effect of internals on the flow pattern and mixing in stirred tanks, Ind. Eng. Chem. Res. 44 (2005) 9951-9961. P. Hasal, M. Jahoda, I. Fo?t, Free liquid surface motions in a stirred tank: an insight into the fluid flow dynamics, Proceedings of CHISA 2006 — 17th International Congress Chemical and Process Engineering, Prague — Czech Republic, 2006. V. Buwa, A. Dewan, A.F. Nassar, F. Durst, Fluid dynamics andmixing of single-phase flow in a stirred vessel with a grid disc impeller: experimental and numerical investigations, Chem. Eng. Sci. 61 (2006) 2815-2822. Y. Bao, L. Chen, Z. Gao, J. Chen, Local void fraction and bubble size distributions in cold-gassed and hot-sparged stirred reactors, Chem. Eng. Sci. 65 (2010) 976-984. N. Otomo, W. Bujalski, A.W. Nienow, K. Takahashi, A novel measurement technique for mixing time in an aerated stirred vessel, J. Chem. Eng. Jpn. 36 (2003) 66-74. M. Martín, M. Rendueles, M. Díaz, Global and local mixing determinations for steel converter analysis, Chem. Eng. Sci. 60 (2005) 5781-5791. P.N. Jones, G.N. Özcan-Ta?kin, Effects of physical property differences on blending, Chem. Eng. Technol. 28 (2005) 908-914. A.B. Pandit, J.B. Joshi,Mixing in mechanically agitated gas-liquid contactors, bubble columns and modified bubble columns, Chem. Eng. Sci. 38 (1983) 1189-1215. B.R. Poulsen, J.J.L. Iversen, Mixing determinations in reactor vessels using linear buffers, Chem. Eng. Sci. 52 (1997) 979-984. J.R. Vallejos, Y. Kostov, M.R. Marten, G. Rao, Confocal optical system: a novel noninvasive sensor to study mixing, Biotechnol. Prog. 21 (2005) 1531-1536. P. Vrábel, R.G.J.M. van der Lans, K.Ch.A.M. Luyben, L. Boon, A.W. Nienow, Mixing in large-scale vessels stirred with multiple radial or radial and axial up-pumping impellers: modeling and measurements, Chem. Eng. Sci. 55 (2000) 5881-5896. G.J.S. van der Gulik, J.G. Wijers, J.T.F. Keurentjes, Hydrodynamics and scale-up of horizontal stirred reactors, Ind. Eng. Chem. Res. 40 (2001) 4731-4740. R.K. Grenville, T.M. Hutchinson, R.W. Higbee, Optimisation of helical ribbon geometry for blending in the laminar regime, Proceedings of Mixing XVIII, North American Mixing Forum, Pocono, U.S.A, 2001. F. Magelli, G. Montante, D. Pinelli, A. Paglianti, Mixing time in high aspect ratio vessels stirred with multiple impellers, Chem. Eng. Sci. 101 (2013) 712-720. D. García-Cortés, E. Ferrer, E. Barberà, Hydrodynamic characterization of the flow induced by a four-bladed disk-style turbine, Chem. Eng. Res. Des. 79 (2001) 269-273. A.W. Nienow, On the impeller circulation andmixing effectiveness in the turbulent flow regime, Chem. Eng. Sci. 52 (1997) 2557-2565. M. Coroneo, G. Montante, A. Paglianti, F. Magelli, CFD prediction of fluid flow and mixing in stirred tanks: numerical issues about the RANS simulations, Comput. Chem. Eng. 35 (2011) 1959-1968. J. Min, Z. Gao, L. Shi, CFD simulation of mixing in a stirred tank with multiple hydrofoil impellers, Chin. J. Chem. Eng. 13 (2005) 583-588. J. Min, Z. Gao, Large eddy simulations of mixing time in a stirred vessel, Chin. J. Chem. Eng. 14 (2006) 1-7.