Flow, Turbulence and Combustion 65: 31–50, 2000. © 2000 Kluwer Academic Publishers. Printed in the Netherlands. 31 Validation of a Two-Dimensional Hyperbolic System Modelling a Gas Fluidized Bed J.W. WILDER ⋆ , I. CHRISTIE and G.H. GANSER Department of Mathematics, West Virginia University, P.O. Box 6310, Morgantown, WV 26506, U.S.A. Received 6 January 1999; accepted in revised form 24 July 2000 Abstract. Numerical solutions of a gas fluidized bed model in two space dimensions are presented. This model is hyperbolic and contains particle pressure, but no particle viscosity. The results are compared with experimental data available in the literature for a wide variety of phenomena. Invest- igated are: the rise velocity of a single, isolated bubble; the frequency of variation of bubble diameter with time; bubble splitting; bubble frequency and the coalescence of a bubble chain formed by gas injected through a single orifice; analysis of the coalescence of bubbles aligned vertically, as well as that of those not in vertical alignment; the formation of slugs in narrow beds; and, eruption at the bed surface. The simulation results show both qualitative and quantitative agreement with the literature. Key words: fluidization, model validation, hyperbolic model. 1. Introduction A fluidized bed consists of a vertical column containing particles. Gas is pumped through a perforated plate at the bottom of the column and flows through the spaces between the particles. When the weight of the particles is first balanced by a suffi- ciently strong upward flow of gas, the bed is at minimum fluidization. Increasing the gas velocity frequently leads to “bubbles” or “slugs” characterized by regions of high and low concentration of particles moving up the bed. Mathematical models of fluidization may or may not include a particle viscosity term in an attempt to model the property of the fluidized particles that resists the force tending to cause them to flow. Some authors [9, 19] suggest that particle viscosity, no matter how small, is essential for the periodic behavior corresponding to slugging to occur. A recent review [15] of the origin of bubbles in both gas and liquid fluidized beds states that the nonlinear theory (i.e., bubbles) depends on the form of the particle viscosity and particle pressure. The work cited in this review is based on results in the weakly nonlinear regime. As will be shown here, it is not necessary to include particle viscosity to model the strongly nonlinear regime with respect to a wide range of experimentally observed behavior of bubbles in gas flu- idized beds. Earlier work [11] utilizing the model employed here has demonstrated ⋆ Author for correspondence.