Experimental study and transient CFD/DEM simulation in a fluidized bed based on different drag models
Gas–solid two-phase flow is the main phenomena in the chemical-looping combustion (CLC) fluidized bed system. Drag force generated from relative movement between phases is the main force that hinders the movement of the oxygen carrier particles. It is important to evaluate and understand the limitations and validity range of different drag models. In this paper, based on Discrete Elements Methods (DEM) coupled with Computational Fluid Dynamics (CFD), three kinds of drag models, Wen-Yu, Syamal-O'Brien, and Gidaspow, are used for the simulation of a laboratory-scale spouted fluidized bed. The numerical results based on these three models are compared and analyzed from the views of the bed height, bubble diameter, and pressure fluctuations. A spouted fluidized bed experiment rig was established to carry out the high-speed imaging experiment and validate the numerical results. All three drag models could basically describe the transient behavior of the bubble shape. In the first stage of whole fluidization process, Syamal-O'Brien drag model could predict well both the change of the bubble diameter and the bubble shape in good agreement with experiment results, but the model for the bubble collapse status is not a good prediction; Wen-Yu drag model underestimates the variations in bubble diameter and predicts the occurrence of the next fluidization stage prematurely; although, the Gidaspow drag model still slightly underestimates the change of bubble diameter, but the results of this drag model are in good agreement with the experiment results in terms of the bubble shape, and pressure fluctuations. Under the architecture of CFD/DEM, the Gidaspow drag model gives the better prediction of the inner flow in the dense gas–solid fluidized bed. The results provide reference for the further improved design of the fluidized bed by employing the CFD/DEM method.