With an increasing spout-fluid ratio, the stable spout–annulus–fountain structure gradually shifts to an unstable bubble–slug structure. This region can be delineated using a single parameter of dimensionless collisional particle pressure because in this region, particle pressure is dominated by the collisional contribution. A transition region between spout and annulus regions is proposed. Analysis on relative contributions of kinetic motion, friction, and collision to particle–particle momentum transfer parameters, namely, particle pressure and viscosity, shows that particle–particle momentum transfer in the spout and fountain regions is dominated by kinetic motion and that in the annulus region is dominated by friction. The drag model of HKL predicts a more reasonable result than models of Huilin-Gidaspow, BVK, and Syamlal and O’Brien. Simulation results show that application of an effective restitution coefficient in TFM can improve the accuracy of prediction significantly. The effects of normal restitution model and gas–solid drag model are assessed by comparing simulation results with the experimental and discrete particle modeling (DPM) data of Link et al. In this paper, a two-fluid model (TFM) is set up to reproduce the various flow structures encountered during spout-fluid bed operation. Spout-fluid beds are widely used in the process industry due to their facilitation of an efficient contact between particles and gas.

Fluid simulation