CFD modeling of pressure drop and drag coefficient in fixed and expanded beds

Abstract

The aim of this study is computational fluid dynamic (CFD) simulation of the single-phase pressure drop in fixed and expanded beds. A fixed bed with a column to particle diameter ratio (D/d_p) of 5 and having 151 particles arranged in 8 layers was taken as a computational geometrical model. In the case of expanded beds, 0.605 voidage bed consisted of 105 particles and 0.783 voidage bed consisted of 55 particles. Simulations were performed in the creeping, transition and turbulent flow regimes, where Reynolds number (d_pV_Lρ_L/μ_L) was varied from 0.1 to 10,000. The deviations from Ergun's equation due to the wall effects, which are important in D/d_p < 10 beds, were well explained by the CFD simulations. Thus, an increase in the pressure drop was observed due to the wall friction in the creeping flow, whereas, in turbulent regime a decrease in the pressure drop was observed due to the channeling near the wall. Energy balance has been established through the CFD predicted values of energy dissipation rates (viscous as well as turbulent).