Gas Bubble Diameter and Rise Velocities in Tapered Fluidized Beds: Experiment and Computational Fluid Dynamics Simulation

The two-dimensional two-fluid model (TFM) incorporating the kinetic theory of granular flow was used to simulate the hydrodynamic behavior of gas bubbles in tapered fluidized beds. Because numerous previous works conducted were mainly focused on the hydrodynamic behavior of the beds such as pressure drop, minimum fluidization velocity, and bed expansion ratio, it is required to investigate one of the most significant parameters in tapered fluidized beds (i.e., gas bubble diameter and rising velocity). The experimental data obtained in our laboratory were compared with the simulation results, and good agreement was found. Effects of the superficial gas velocity, apex angle, particle size, particle density, Geldart groups, initial bed height, operating pressure, and performances of various drag models were investigated carefully. It was found that Syamlal–O’Brien’s drag model provides the best predictions for the gas bubble behavior with an RMSE of 11.4% (Syamlal, M.; O’Brien, T. J. Computer simulation of bubbles in a fluidized bed. AIChE Symp. Ser., 1989, 85, 22–31). In addition, with an increase in the particle density and size, operating pressure, and initial bed height, the gas bubble diameter and rising velocity decrease. Moreover, the gas bubble diameter decreases with an increase in the apex angle; however, no significant changes were observed in the gas bubble rising velocity. Furthermore, the gas bubble diameter and rising velocity were much larger for Geldart A particles.