A CPFD Simulation on Hydrodynamics of Carbon Nanotube Aggregates in a Fluidized Bed

Abstract

A computational particle–fluid dynamics (CPFD) model of a fluidized bed reactor with carbon nanotube (CNT, d_p = 485 μm) particles was established. A drag model and coefficient were determined to simulate the hydrodynamic behavior of CNTs in a fluidized bed. The drag coefficient reflected the variation in physical properties owing to CNT agglomeration, such as aggregate size distribution, particle circularity, and apparent density. The Richardson–Davidson–Harrison model with a drag coefficient of 0.17 was chosen based on results on solid holdup distribution. The proposed CPFD model described hydrodynamic behaviors, such as bed expansion, solid holdup distribution, and relative standard deviation (RSD) of the pressure drop with gas velocity, and predicted the transition gas velocity between the partial and complete fluidization regimes. The bed expansion and RSD gradually increased with increasing gas velocity in the partial fluidization regime and rapidly increased at the beginning of the complete fluidization regime. The increased gas velocity significantly enhanced bed expansion and particle entrainment, resulting in the formation of large CNT aggregates and a higher solid holdup in the freeboard in the complete fluidization regime. The simulated results describe the behavior of CNT aggregates near the bed surface and in the freeboard region, supporting previous findings in the literature. Uneven local gas flows occurred in the bed and freeboard regions, and the results described the bubbling bed characteristics in the complete fluidization regime.