A comparative study on the influence of the gas flow rate on the hydrodynamics of a gas-solid spouted fluidized bed using Euler-Euler and Euler-Lagrange/DEM models

In this work, different modeling approaches are used to study the hydrodynamics of gas-solid flows in a three-dimensional, lab-scale spouted fluidized bed. In particular, the simulation results obtained by the two-fluid model are compared with those of coupled CFD/DEM simulations. To explore the effects of the gas mass flow rate on the ability of the used simulation techniques to predict the flow behavior in the simulated test case, two different fluidization conditions are considered while maintaining the same computational set-up. The spouted fluidized bed has been evaluated by means of high-speed imaging for validating the simulation results. A comparative,study of the two modeling approaches with experimental observations for bubble size in terms of the representative bubble diameter and the bed height has been carried out under both operating conditions. To identify significant simulation settings for the two-fluid model, a parameter study is carried out. The investigated input parameters include the gas-particle drag models, the granular temperature approach, the solid-phase wall boundary conditions in terms of specularity coefficient and the particle-particle restitution coefficient At a gas mass flow rate of 0.005 kg/s, the predicted characteristics of the bubble formation and the bed expansion using both techniques are in very good agreement with experimental observations. Using the same validated settings, the two-fluid model shows some notable discrepancies when the gas mass flow rate is increased to 0.006 kg/s, while the DEM is more successful than the two-fluid model in reproducing realistic flow patterns. Although both techniques predict the right fluidization regimes and trends in bubble sizes and bed expansion, their results deviate significantly from the experimental data during the final stage of the bubble formation. The most important reasons for the differences in predicting the bed dynamics along with the advantages and limitations of the two approaches are discussed. (C) 2014 Elsevier B.V. All rights reserved.