关键词: 流态化, 计算流体力学, 流体动力学, 双流体模型, 液固两相流, 颗粒黏性

Abstract:

In order to probe into the effect of particle viscosity on homogeneous liquid-solid fluidization, three types of two-fluid models including inviscid TFM Gidaspow A (ITFM), TFM based on KTGF (KTFM) and Brandani and Zhang simplified TFM (STFM) are used for CFD simulations in this study. The numerical results are compared with the typical experimental data from the literature and calculated values by Gibilaro formula, which shows that all three two-fluid models can reasonable predict the overall solid holdup together with all relative deviations between each two-fluid model and the experimental data are less than 3%. The solid holdup obtained by ITFM or STFM is more consistent with the characteristics of homogeneous fluidization. The three two-fluid models all show the inherent properties of the overall ring-core structure for the prediction of the time-averaged particle axial velocity. Among them, the average relative deviations of the simplified two-fluid model under the two groups of low and high liquid velocity conditions are 0.277 and 1.028 respectively. STFM is slightly closer to calculated value by Gibilaro formula than the other two models in predicting the response time of contraction process. However, the predictions of all three models deviate from the ideal process, mainly due to the extended stability time caused by the instability of the low concentration interface and the transitional stage from dense to dilute regions of particles in expansion process. In expansion process, the differences among the three models are not obvious at low operating velocity, while the result of STFM is slightly closer to calculated value by Gibilaro formula at high operating velocity. KTFM takes the longest elapsed time for simulating dynamic processes in this study.

Key words: fluidization, CFD, hydrodynamics, two-fluid model, liquid-solid two-phase flow, particle viscosity