Abstract: A mathematical model, including additional terms in both the gas- 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 homogenous fluidization of Geldart A particle and bubbling/collapsing fluidization of Geldart B particle in 3D gas-fluidized beds.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.Transient calculations within the bed of 0.2 m (long) × 0.2 m (wide) × 0.5 m (high) were conducted in the platform of a commercial software package, CFX 4.4, by adding user-defined Fortran subroutines.To verify the mathematical model and numerical procedure, two kinds of Geldart A particles were simulated at superficial gas velocity of u_mf and 1.5u_mf, and the results showed homogenously expanding behavior in nature.Then the effect of disturbances on local voidage and solid velocity profile at the grid scale, and overall bed pressure drop at the equipment scale were investigated numerically for two kinds of Geldart A particles.Bubbling and collapsing behavior at the grid scale, and overall bed pressure drop during bubbling process and averaged bed height and the standard deviation of the interface during the collapse process at the equipment scale were probed for one kind of Geldart B particles.The above numerical simulations were in fair agreement with the classic theory of Geldart, experiment and simulation in the literature, indicating that this model can be used to predict homogeneous fluidization of Geldart A particles and bubbling and collapsing behavior of Geldart B particles in 3D fluidized beds.

Key words:

气固流化床, 三维CFD模拟, Geldart A和B物料, 散式/鼓泡/塌落特性

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到基于双流体理论动量方程的数学模型中，用于Geldart A类物料散式流态化和B类物料鼓泡/床层塌落特性的三维数值模拟。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模拟了长0.2 m、宽0.2 m和高0.5 m流化床内瞬态流动特性。为了检验数学模型的实用性和数值模拟的可靠性，首先考察了两种A类物料在表观气速为u_mf和1.5u_mf下的散式流态化特性，结果展示出床层均匀膨胀的固有属性。随后，考察了扰动对A类物料在网格尺度上的局部空隙率和固体速度分布以及在设备尺度上床层压降的影响，探索了B类物料在网格尺度上鼓泡和床层塌落以及在设备尺度上鼓泡过程中床层压降和塌落过程中平均床层高度和相界面标准偏差的动态特性。上述模拟结果与经典的Geldart理论、前人的实验或模拟结果相吻合，说明该模型可以用来预报三维气固流化床内A类物料散式流态化和B类物料鼓泡及塌落的时空特性。

关键词:

气固流化床, 三维CFD模拟, Geldart A和B物料, 散式/鼓泡/塌落特性