A mathematical model

including additional terms in both the liquid- 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 hydrodynamics in a 0.1 m (long) × 0.1 m (wide) × 0.5 m (high) 3D fluidized bed.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.Water and particles with a diameter of 2.5×10-3 m and density of 3000 kg·m-3 were used as liquid and solid phases

respectively.Spatio-temporal evolutions were simulated in the platform of CFX 4.4 by adding user-defined Fortran subroutines as liquid inlet velocity was suddenly changed.When liquid inlet velocity increased

both the internal interface and bed surface increased with simulation time

but the internal interface was wave-shaped.When liquid inlet velocity decreased

however

increasing internal interface and decreasing bed surface exhibited linear relation with time.Meanwhile

simulated transient response time was in good agreement with the two-dimensional experiments of Didwanla and Homsy and the one-dimensional theory of Gibilaro

indicating that this model could be used to predict the hydrodynamics of liquid-solid system in three-dimensional fluidized beds.