Verification of semi-empirical relations for predicting fluidization in a fluidized bed using CFD

Abstract

The main objective of this study is to verify different (semi)empirical formulas used to predict hydrodynamic parameters of a fluidized bed against CFD simulations. The hydrodynamic parameters investigated include minimum fluidization velocity, bed voidage at minimum fluidization condition, bubble diameter, and bubble velocity. All simulations were completed using a 3D Euler-Euler-based model available in ANSYS Fluent 19.2. The study of solid volume-averaged velocity inside the bed revealed a minimum fluidization velocity of 0.194m/s, which was in agreement with the result obtained when the pressure drop in a fluidized bed was set equal to that in a fixed bed. The time-averaged solid volume fraction showed that the constant value of 0.476 (with the assumption of the uniform cubic mode of packing) was a good estimation for bed voidage at minimum fluidization condition. The study of air turbulent viscosity demonstrated high air turbulence above the bed and inside large bubbles within the bed. Higher mean bed heights and higher levels of air circulation were observed at higher air flowrates. The analysis of different formulas predicting bubble diameter and bubble velocity at different bed heights and air flowrates showed that Yasui-Johnson's formula for estimating the bubble diameter could produce results in good agreement with our CFD simulations for the tested geometry and initial conditions.