Abstract:

A mathematical model, including additional terms in both the liquid- and solid-phase momentum equations based on the two-fluid theory by considering particle-fluid interactions under a quasi-equilibrium state, was employed to explore hydrodynamics in a 0.1 m (long) × 0.1 m (wide) × 0.5 m (high) 3D fluidized bed.The main features of this model are that the characteristic length in the model is of the order of the particle diameter and only a correlation for drag force coefficient is necessary to close the governing equations.Water and particles with a diameter of 2.5×10^-3 m and density of 3000 kg·m^-3 were used as liquid and solid phases, respectively.Spatio-temporal evolutions were simulated in the platform of CFX 4.4 by adding user-defined Fortran subroutines as liquid inlet velocity was suddenly changed.When liquid inlet velocity increased, both the internal interface and bed surface increased with simulation time, but the internal interface was wave-shaped.When liquid inlet velocity decreased, however, increasing internal interface and decreasing bed surface exhibited linear relation with time.Meanwhile, simulated transient response time was in good agreement with the two-dimensional experiments of Didwanla and Homsy and the one-dimensional theory of Gibilaro, indicating that this model could be used to predict the hydrodynamics of liquid-solid system in three-dimensional fluidized beds.

Key words:

液固流化床, 三维CFD模拟, 床层膨胀, 床层收缩

摘要：

将考虑拟平衡状态下颗粒与流体相互作用的附加力添加在基于双流体理论的动量方程中的数学模型，用于预报三维液固流化床内流体动力学特性。该模型主要特点是将表征颗粒离散属性的特征长度视为颗粒直径的同一数量级且只需曳力系数一个关联式来封闭控制方程。在商业软件CFX4.4平台上，通过增加用户自定义子程序考察了液体速度突变后水-颗粒（密度3000 kg·m^-3，粒径为2.5×10^-3 m）体系在长0.1 m、宽0.1 m和高0.5 m流化床内时空分布特性。三维、X和Y方向中间截面上固含率的模拟结果表明：当液体入口速度增大时，床层表面和分隔界面均随时间呈上升趋势，且分隔界面呈现波浪状;当液体入口速度减小时，下降的床层表面和上升的分隔界面与时间呈较好的线性关系。对床层膨胀和收缩过程的动态响应时间进行了定量化模拟，其结果与Didwanla和Homsy的二维实验研究以及Gibilaro的一维理论分析相吻合。

关键词:

液固流化床, 三维CFD模拟, 床层膨胀, 床层收缩