Enhancement of Laminar Mixing in Stirred Vessel using Geometrical Perturbations

 

A. Hidalgo-Millán¹, B. Taboada², L. Vega-Alvarado³, R. Zenit⁴, Gabriel Ascanio*³

 

¹ Unidad Académica de Ciencias Básicas e Ingeniería Universidad Autónoma de Nayarit, Tepic, Nayarit, México.

² Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, México.

³ Centro de Ciencias Aplicadas y Desarrollo Tecnológico, Universidad Nacional Autónoma de México, México, D. F., México, *gabriel.ascanio@ccadet.unam.mx.

⁴ Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México, México DF, México.

 

ABSTRACT

Geometrical perturbations by using single and coaxial impellers configurations have been investigated in the laminar regime (Re = 2.68) in unbaffled stirred vessels. Combinations of one and two coaxial radial discharge flow impellers under centered and eccentric conditions were studied with viscous Newtonian fluid. The study of geometrical perturbations has been made in terms of the mixing times, energy consumption and the flow fields. Homogenization degrees and mixing times, determined with a color-discoloration technique, were evaluated by means of image processing. The flow fields were investigated using the particle image velocimetry technique. The use of off-centered impellers increases the pumping capacity; however, little effect of eccentricity was obtained when using two coaxial impellers under off-centered conditions obtaining the best results with a novel configuration consisting of a dual turbine with connecting plates.

Keywords: Mixing, laminar flow, visualization, hydrodynamics, stirred vessels, eccentric impellers.

 

RESUMEN

Se presentan los resultados de la investigación en tanques agitados en régimen laminar (Re = 2.68) con impulsores sencillos y coaxiales. Para ello se han elegido combinaciones de uno y dos agitadores de descarga radial centrados y descentrados con respecto al tanque empleando fluidos newtonianos. El estudio se llevó a cabo en términos del tiempo de mezclado mediante la técnica de colorimetría y procesamiento de imágenes. Los campos de flujo se obtuvieron por medio de la técnica de velocimetría de imágenes de partículas (PIV por sus siglas en inglés). Se observó un incremento en la capacidad de bombeo empleando un impulsor excéntrico. Sin embargo, el efecto fue menor al emplear dos impulsores coaxiales en posición descentrada. Por tal motivo se propuso una nueva configuración a base de dos agitadores coaxiales conectados mediante un par de barras.

 

DESCARGAR ARTÍCULO EN FORMATO PDF

 

Acknowledgements

The financial support from DGAPA-UNAM grant IN-108312 and from National Council of Science and Technology (CONACyT) grant 123840 are highly appreciated. The technical advice and assistance during PIV experiments from Carlos Palacios is also acknowledged.

 

References

[1] L. Bresler, T. Shinbrot, G. Metcalfe, J.M. Ottino, "Isolated mixing regions: origin, robustness and control", Chem. Eng. Sci., vol. 52, no. 10, pp. 1623-1636, 1997.         [ Links ]

[2] P. Mavros, "Flow visualization in stirred vessels, A review of experimental techniques", Trans. Inst. Chem. Eng. Part A, vol. 79, no.2, pp. 113-127, 2001.         [ Links ]

[3] A.B. Norwood, A.B. Metzner, "Flow patterns and mixing rates in agitated vessels", AIChE J., vol. 6, no. 3, pp. 432-437, 1960.         [ Links ]

[4] T.P. Elson, D.J. Cheesman, A.W. Nienow, "X-ray studies of cavern sizes and mixing performance with fluids possessing a yield stress", Chem. Eng. Sci., vol. 41, no. 10, pp. 2555-2562, 1986.         [ Links ]

[5] 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", Trans. Inst. Chem. Eng. vol. 77, no. 8, pp. 709-712, 1999.         [ Links ]

[6] E. Brito-de la Fuente, S. Hernández, A. Segura, L. Medina, P. A. Tanguy, G. Ascanio, "Laminar mixing in stirred tanks using dynamics perturbations and non-symmetric geometry conditions", Proceedings of the VI Pan-American Congress in Applied Mechanics, Rio de Janeiro, Brazil, 1999.         [ Links ]

[7] G. Ascanio, M. Brito-Bazan, 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. vol. 80, no. 4, pp. 558-565, 2002.         [ Links ]

[8] H. Aref, "Stirring by chaotic advection", J. Fluid Mech., vol. 143, pp. 1-21, 1984.         [ Links ]

[9] H. Aref, S. Balachandar, "Chaotic advection in a Stokes flow", Phys. Fluids. vol. 29, no. 11, 1986, pp. 3515-3521, 1986.         [ Links ]

[10] J.G. Franjione, C.W. Leong, J.M. Ottino, "Symmetries within chaos: A route to effective mixing". Phys. Fluids, vol. 1, no. 11, pp. 1772-1783, 1989.         [ Links ]

[11] M. Alvarez, P.E. Arratia, F.J. Muzzio, "Laminar mixing in eccentric stirred tank systems", Can. J. Chem. Eng., vol. 80, no. 4, pp. 546-557, 2002.         [ Links ]

[12] G. Montante, A. Bakker, A. Paglianti, F. Magelli, "Effect of the shaft eccentricity on the hydrodynamics of unbaffled stirred tanks", Chem. Eng. Sci., vol. 61, no. 9, pp. 2807-2814, 2006.         [ Links ]

[13] J. Karcz, M. Cudak, J. Szoplik, "Stirring of a liquid in a stirred tank with an eccentrically located impeller", Chem. Eng. Sci., vol. 60, no. 8-9, pp. 2369-2380, 2005.         [ Links ]

[14] C. Galletti, E. Brunazzi, "On the main flow features and instabilities in an unbaffled vessel agitated with an eccentrically located impeller", Chem. Eng. Sci., 63(18), 4494-4505, 2008.         [ Links ]

[15] C. Galletti, S. Pintus, E. Brunazzi, E. "Effect of shaft eccentricity and impeller blade thickness on the vortices features in an unbaffled vessel", Chem. Eng. Res. Des., vol. 87, no. 4, pp. 391-400, 2009.         [ Links ]

[16] J.M. Ottino, C.W. Leong, H. Rising, P.D. Swanson, "Morphological structures produced by mixing in chaotic flows", Nature, vol. 333, pp. 419-425, 1988.         [ Links ]

[17] P.D. Swanson, J. M. Ottino, "Comparative computational and experimental study of chaotic mixing of viscous fluids", J. Fluid Mech. vol. 213, 1990, pp. 227-249.         [ Links ]

[18] F.J. Muzzio, P.D. Swanson, J. M. Ottino, The statics of stretching and starting in chaotic flows, Phys. Fluids, vol. A 3, no. 5, pp. 822-834, 1991.         [ Links ]

[19] F.J. Muzzio, C. Meneveau C., P. D. Swanson, J. M. Ottino, "Scaling and multifractal properties of mixing in chaotic flows", Phys. Fluids, vol. A 4, no. 7, pp. 1439-1456, 1992.         [ Links ]

[20] G. Ascanio, P. A. Tanguy, "Mixing of shear-thinning fluids with dual off-centered impellers", Can. J. Chem. Eng., vol. 83, no. 3, pp. 393-400, 2005.         [ Links ]

[21 ] D.J. Lamberto, F. J. Muzzio, P. D. Swanson, "Using time-dependent RPM to enhance mixing in stirred vessels", Chem. Eng. Sci., vol. 51, no. 5, pp. 733-741, 1996.         [ Links ]

[22] K. Plataniotis , A. Venetsanopoulos, "Color image processing and applications" Germany, Springer, 2000.         [ Links ]

[23] M. Rice, J. Hall, G. Papadakis, M. Yianneskis, "Investigation of laminar flow in a stirred vessel at low Reynolds numbers", Chem. Eng. Sci., vol. 61, no. 9, pp. 2762-2770, 2006.         [ Links ]