A mathematical model

including additional terms in both the gas- and solid-phase momentum equations based on the two-fluid theory by considering particle-fluid interactions under a quasi-equilibrium state

was employed to explore homogenous fluidization of Geldart A particle and bubbling/collapsing fluidization of Geldart B particle in 3D gas-fluidized beds.The main features of this model are that the characteristic length in the model is of the order of the particle diameter and only a correlation for drag force coefficient is necessary to close the governing equations.Transient calculations within the bed of 0.2 m (long) × 0.2 m (wide) × 0.5 m (high) were conducted in the platform of a commercial software package

CFX 4.4

by adding user-defined Fortran subroutines.To verify the mathematical model and numerical procedure

two kinds of Geldart A particles were simulated at superficial gas velocity of umf and 1.5umf

and the results showed homogenously expanding behavior in nature.Then the effect of disturbances on local voidage and solid velocity profile at the grid scale

and overall bed pressure drop at the equipment scale were investigated numerically for two kinds of Geldart A particles.Bubbling and collapsing behavior at the grid scale

and overall bed pressure drop during bubbling process and averaged bed height and the standard deviation of the interface during the collapse process at the equipment scale were probed for one kind of Geldart B particles.The above numerical simulations were in fair agreement with the classic theory of Geldart

experiment and simulation in the literature

indicating that this model can be used to predict homogeneous fluidization of Geldart A particles and bubbling and collapsing behavior of Geldart B particles in 3D fluidized beds.