Brief communication Hydrodynamics of particle segregation in fluidized beds Dinesh Gera a,* , Madhava Syamlal a , Thomas J. OÕBrien b,1 a Fluent Incorporated, 3647 Collins Ferry Road, Suite A, Morgantown, WV 26505, USA b US Department of Energy, 3610 Collins Ferry Road, MS-N04, Morgantown, WV 26505, USA Received 14 July 2003; received in revised form 14 November 2003 1. Introduction Research in multiple particulate phase hydrodynamics is important in many industrial appli- cations that involve segregation or mixing processes, specifically in mineral classification, elutri- ation, sedimentation, crystallization and fluid bed leaching, just to name a few. There have been several investigations dealing with segregation and mixing of particles of different sizes and densities in fluidized bed reactors or classifiers (Chen et al., 2002). The studies show that particles will segregate into layers if a bed, consisting of two different size particles with the same density, is fluidized with a velocity that is in between the individual minimum fluidization ðu mf Þ velocities for each particle type. The binary system will not segregate if the fluidizing velocity is higher than the u mf of the larger particles; rather the particles mix vigorously. The models reported in the liter- ature are able to predict the segregation of the particles at an intermediate fluidization velocity (Goldschmidt et al., 2001). However, they predict particle segregation even at a low fluidization velocity, when segregation is not observed. In this study we modified the particle–particle drag term so that the model predicts no segregation at low velocities, segregation at intermediate velocities, and mixing at high velocities. Furthermore we show that the predicted rate of segre- gation at intermediate velocities agrees quantitatively with experimental data. In the last decade, considerable efforts have been made in developing detailed hydrodynamic tools for the simulation of fluidized bed dynamics, including Eulerian/Lagrangian, and the hybrid Eulerian/Lagrangian mapping methods. Eulerian/Eulerian methods consider the primary and secondary (dispersed) phases to be interpenetrating continua, and the equations employed are generalizations of the Navier–Stokes equations (e.g., Gidaspow, 1994). Eulerian/Lagrangian models describe the primary phase flow using the continuum equations, and the particulate phase International Journal of Multiphase Flow 30 (2004) 419–428 www.elsevier.com/locate/ijmulflow * Corresponding author. Tel.: +1-304-598-7934; fax: +1-304-598-7185. E-mail addresses: dfg@fluent.com (D. Gera), tobrie@netl.doe.gov (T.J. OÕBrien). 1 Tel.: +1-304-285-4571. 0301-9322/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.ijmultiphaseflow.2004.01.003