Computation of system turbulences and dispersion coefficients in circulating fluidized bed downer using CFD simulation

摘要

In this study, the Eulerian computational fluid dynamics model with the kinetic theory of granular flow model was effectively used to compute the system turbulences and dispersion coefficients in a circulating fluidized bed (CFB) downer. In addition, the obtained model was used to simulate all the system velocities. The system turbulences, which were the granular temperatures and turbulent kinetic energies, and dispersion coefficients were investigated and employed as an explanation for the system hydrodynamics. The laminar granular temperatures were higher than the turbulent ones, which implies that an individual gas/solid particle oscillation dominates the flow structure in the CFB downer. There was a good agreement between the total granular temperature values in this study and those in the literature. The obtained turbulent kinetic energies varied within two orders of magnitude, but their values remained low. At increasing depths in the CFB downer, the turbulent kinetic energies were directly increased due to the formation of more gas bubble/solid particle clusters. The laminar and turbulent dispersion coefficients were significantly higher and lower, respectively, when compared to the previously reported ones. This shows the improper mixing of the gas bubble/solid particle cluster inside the CFB downer when compared to the individual movement ones.