Study of Hybrid Drag Models For Predicting Hydrodynamic Behaviour in a Spouted Bed D. A. Santos, I. J. Petri, C. R. Duarte and M. A. S. Barrozo* School of Chemical Engineering, Federal University of Uberlândia, Bloco K, Campus Santa Mônica, PO Box 593, 38400‐902, Uberlândia, MG, Brazil A hybridisation study of drag models was performed in a conical–cylindrical spouted bed by means of CFD simulations using an Eulerian–Eulerian multiphase model. In order to evaluate the simulation results, time‐averaged velocity distributions of the particulate phase were compared with the experimental data obtained by means of an optical fibre probe. The hybrid drag model considering both the volume fraction and the granular temperature distribution in the drag force calculation predicted the experimental data of the particle velocity distribution better than the other simulations performed in this work using other hybrid drag models. Keywords: CFD, multiphase model, optical fibre probe INTRODUCTION S pouted beds are used in many processes of great interest, such as drying of granular materials, [1,2] coating of particles, [3] gasification [4] and pyrolysis, [5] mechanical extraction, [6] seeds inoculation [7] and coating, [8] although most of these are still under research and development. In these processes an effective contact between the phases involved is essential to reach higher mass transfer, energy and momentum rates. Besides their ability to handle coarse particles, spouted beds have structural and cyclic flow patterns with effective fluid–solid contact. [9] Spouted beds are divided into three different regions, each with its own specific flow behaviour, thus its study increases in complexity: a spout at the centre, where the gas and particles rise at high velocity and the particle concentration is low; a fountain zone, where particles rise to their highest positions and then rain back onto the surface of the annulus; and an annulus zone between the spout and the column wall where particles move slowly downward as a dense phase. The mechanisms of solid movement in spouted beds are still not completely understood. Knowledge of solid flow patterns in spouted beds is essential to their design, because the particles’ trajectories must meet process requirements. Thus, among many other variables, the particle velocity distribution has received considerable attention. [10] There are different techniques to measure this property. [11–14] The optical fibre probe is a relatively simple and robust technique, which promotes minimum disturbance to the flow field, depending on its geometry. This probe exhibits chemical stability, thermal tolerance, electrical passivity and immunity to electromagnetic interference. [15] Many researchers have used optical fibre probes in systems containing dense phases, such as in fluidised beds, [16] in conical spouted beds, [10] in conical– cylindrical spouted beds [17–19] and jet spouted beds. [20] With today’s rapid computational development, such as improvements in data processing and storage, a useful tool to obtain detailed information on flow phenomena has emerged, known as computational fluid dynamics (CFD). Numerical simulation studies using the CFD technique have become popular in the field of gas–solid flow. However, this great technological advantage contrasts with the scarce experimental data, which are fundamentally important to validate mathematical models. The two approaches commonly used in the simulation of multiphase flows are the Euler–Lagrange and the Euler–Euler. In the Euler–Lagrange approach, the fluid phase is treated as a continuum by solving the time average Navier–Stokes equations, while the dispersed phase is solved by tracking a large number of particles (or bubbles, droplets) through the calculated flow field. This approach is suitable for particle volume fractions less than 0.1. [21] In the Euler–Euler approach, the different phases are treated mathematically as interpenetrating continua. Since the volume of a phase cannot be occupied by the other phases, the volume fraction concept is introduced. These volume fractions are assumed to be continuous functions of space and time and their sum is equal to one. [21] In both approaches the gas phase is described by a locally averaged Navier–Stokes equation and the two phases are usually coupled by a drag force. Due to the large density difference between the particles and the gas, inter‐phase forces other than the drag force are usually neglected, thus playing a significant role in characterising the gas–solid flow. [22] Duarte et al. [12] and Du et al. [23] used the Euler–Euler approach in two‐dimensional simulations to obtain the solid velocity profile and porosity profile in a spouted bed, which were compared with the experiments conducted by He et al. [17] . To calculate the stress distribution in the granular phase, granular viscosity and granular pressure, the kinetic theory of granular flow developed by Lun et al. [24] was used. The authors devised good predictions using this model. Many other researchers have adopted this kind of approach *Author to whom correspondence may be addressed. E‐mail address: masbarrozo@ufu.br Can. J. Chem. Eng. 9999:1–10, 2013 © 2013 Canadian Society for Chemical Engineering DOI 10.1002/cjce.21866 Published online in Wiley Online Library (wileyonlinelibrary.com). VOLUME 9999, 2013 THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING 1