A model Based on Two-fluid Theory for Predicting Hydrodynamic Behavior in 3D Fluidized Bed: II. Fluid Dynamics in Liquid-Solid Systems
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.