Homogeneous and bubbling fluidization regimes in DEM-CFD simulations: Hydrodynamic stability of gas and liquid fluidized beds

In recent years coupled DEM-CFD models have been successfully utilized to simulate fluidized particle systems in the bubbling regime. In this paper we report on DEM-CFD simulations of liquid-fluidization of glass beads and gas-fluidization of Geldart's Group A particles carried out to characterize hydrodynamically the stability of the fluidized state, in the absence of cohesive forces. Due to the importance of the fluid-particle interaction, the two-way coupling approach used is introduced within a rigorous framework. Simulations of 200 Pm glass particles fluidized by water are presented. Homogeneous (particulate) fluidization is obtained for a wide range of velocities, in quantitative agreement with the theory of stability of the fluidized state and with experiments. The possibility of fine particles (70 Put porous alumina, Geldart's Group A) to be air-fluidized homogeneously, without the need to impose inter-particle (cohesive) forces, is demonstrated by means of the first principles analysis guaranteed by the DEM-CFD approach. The appearance of bubbles in the fluidized bed behaviour is shown to occur at velocities in quantitative agreement with the theory of fluidized bed stability. In this context, the transient behaviour of the two systems considered in response to changes of fluid superficial velocity is analysed, allowing to validate the capability of the numerical model to capture the propagation of voidage shocks along bed height. (c) 2006 Elsevier Ltd. All rights reserved.