Prediction of hydrodynamic characteristics of a 3D liquid-solid tapered fluidized bed using kinetic theory of rough spheres

The fluidized bed bioreactor is an economical and efficient method for wastewater treatment. In the fluidized bed bioreactor, fluidized particles carrying microorganisms consume the organic pollutants in wastewater. The collision and friction between carrier particles in the fluidized bed can affect the efficiency of wastewater treatment. Therefore, understanding the hydrodynamics of fluidized bed bioreactors is crucial. In this study, the particle collision velocity depending on particle volume fraction and granular temperature, as well as considering the influence of particle surface roughness and elasticity through the critical Stokes number, a dynamic restitution coefficient model for wet rough particles is developed to provide a more accurate description of the collision behavior between wet rough particles. The model is incorporated into the kinetic theory of rough spheres to perform numerical simulations on the hydrodynamic characteristics of a three-dimensional liquid-solid tapered fluidized bed using the two-fluid model. The simulation results exhibit better agreement with experimental data by Wu et al. compared to prior studies. Furthermore, sensitivity analyses are conducted on drag force, virtual mass force, and lift force. It is observed that the Koch-Hill drag model predicts the bed expansion heights closest to the measured results. Additionally, the impacts of static bed height and particle density on the fluidized bed hydrodynamics are investigated. Simulation results indicate that an increase in static bed height initially leads to an increase and then a decrease in particle collision velocity. Within the current study scope, particle collision velocity exhibits a monotonic increase with increasing particle density.