A simple two-fluid model is used to predict the hydrodynamics of liquid-solid fluidization after a step change in liquid velocity. Based on the inviscid model A of Gidaspow (1994), the effect of the particles dispersed on the momentum equations is considered in this model. Numerical simulations are conducted in the platform of CFX 4.4, a commercial CFD code, together with user-defined FORTRAN subroutines. Predicted overall bed voidage in this work is much closer to the experimental measurement than that based on the kinetic theory of granular flow in the literature (Cornelissen et al., 2007). The results show that the computational bed heights in the expansion process fit in with the idealized curve except at the transitional stage, which leads to actual response time slightly greater than its corresponding idealized value. Non-uniform liquid velocity inlet condition has a strong effect on the transient solid volume fraction within the bed and the response time of bed surface. In the contraction process, however, the transient bed height and response time follow exactly the idealized predictions for either uniform or wave-shaped liquid inlet condition. (C) 2012 Elsevier B.V. All rights reserved.