Cylindrical‐conical spouted bed dynamics: Laminar and turbulent flow predictions

Abstract

AbstractThis work numerically studies transient behaviour of particulate flows in a cylindrical‐conical spouted bed in terms of comparative analysis of different models’ predictions. Two approaches were used: a laminar flow model and a turbulent flow model. As a reference case, we consider experimental studies by He et al.,[14,15] where the profiles of vertical particle velocities and the void fraction in the spout and the fountain of a full‐column spout bed were measured. In this work we used the Euler‐Euler unsteady multiphase model with the Syamlal‐O'Brien, Gidaspow, and Wen‐Yu drag models available in commercial CFD software Fluent 14.0. Analysis of results obtained by the use of laminar and turbulent flow models revealed almost identical solid and gas phase velocities and phase fractions within the spouted bed region. We found that the turbulence plays a significant role only in the gas phase above the spouted bed and it does not have any influence on the solid phase. Comparing our simulation results in the form of time‐averaged vertical velocity of the solid phase against experimental data showed acceptable agreement in the spout and very good agreement in the fountain region. Numerical simulations with the Syamlal‐O'Brien drag model gave better agreement with experimental data than results obtained using the Gidaspow and Wen‐Yu drag models. To analyze the transient behaviour of the spouted bed, we use the volume‐averaged particle velocity and gas phase velocity. The analysis of their time histories showed that the start up time is 2–3 s. The developed unsteady regime is reached after 4–5 s. Additionally we studied numerically the influence of different discretization schemes for convective terms on the final results. We found that the use of 1st order upwind scheme gives a steady state solution for both models, laminar and turbulent. Finally, we investigated the influence of the restitution coefficient on the transient characteristics of a cylindrical‐conical spouted bed. A decrease in the value of the restitution coefficient leads to an increase in the period of oscillations of the volume‐averaged velocities of the gas and solid phases.