| In the study of drag model,the accurate description of the interphase exchange coefficient model and the single particle drag force model is the difficulty of simulation of gas-solid two-phase flow.In this paper,three interphase exchange coefficient models of Huilin-Gidaspow,Gidaspow and Syamal-Obrien are modified by the presemt single particle drag force model based on fractal dimension.The modified Huilin-Gidaspow model is more conformed to the conclusion that the nano cluster fluidization is not bubble,non core-annular and high expansion rate of bed layer.The present drag model is simulated under different fractal dimensions.The results show that with the increase of fractal dimension,the fluidization height increases,the solid holdup is reduced,and the stability of axial radial solid content increases.The present model and the empirical formula based solid ball solid drag model,the uniform drag model based on the fixed permeability and the two layer drag model based on the double layer permeability structure are simulated under different wind speeds.The simulation results show that the fluidization velocity and the drag force model affect the final fluidization height.The flow characteristics of different models also show great differences: the Solid model and the uniform model have the characteristics of the flow of the FCC particle ring core;the two layer model has bubbles in the larger wind speed and the opposite direction of the velocity on both sides of the side wall;the present model has no obvious ring core flow,no gas bubble,whirlpool,and good gas solid mixing.The simulation results are compared with the experimental data.In the three multi hole ball force model,the present model is more accurate and applicable when the wind speed is 5cm/s-7cm/s and the position is in the middle and lower parts.Therefore,the self fitted radial variable permeability model can predict the agglomeration fluidization characteristics of nanoparticles to a certain extent. |
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