气固流化床内射流穿透深度的CFD模拟及其实验验证

CFD simulation of jet penetration depth in gas-solid fluidized bed:comparisons with experiments

在经典的Gidaspow无黏性双流体模型中考虑离散颗粒对流体和固体动量守恒方程的影响后,建立了一个具有模拟大规模流化床内气固两相流体动力学特性潜在优势的简化数学模型。在CFX4.4商业化软件平台上通过增加用户自定义子程序考察了二维气固流化床(高2.00 m、宽0.30 m)内射流气速、喷嘴尺寸、环隙气速和静床高度对射流穿透深度的影响,并以树脂颗粒(粒径670μm、密度1474 kg.m-3)为研究对象在厚度为0.025 m的矩形床内进行了对比实验。结果表明,选取空隙率为0.8的等高线作为射流边界比较合适;射流穿透深度随射流气速或射流喷口尺寸的增加而增大;射流周围环隙气速由0变到最小流化速度时,射流穿透深度随环隙气速增加而增大,在最小流化速度时达到最大值,然后随环隙气速增加单调减小,当环隙气速大于2.5倍最小流化速度时,射流穿透深度减小程度变缓;在相同射流气速下射流穿透深度随着静床高度的增加而减小,静床高度对射流穿透深度的影响随着射流气速增加呈现扩大的趋势。

A simple hydrodynamic 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 quasiequilibrium state, was used to investigate numerically the effects of jet gas velocity, slit size, annular gas velocity and static bed height on the jet penetration depth in gas-solid fluidized beds, CFD simulations were conducted for a 2.00 m （high） × 0.30 m （wide） two-dimensional bed with a central jet and the corresponding experiments were carried out in the rectangle fluidized bed with a thickness of 0. 025 m under the same operating conditions. Resin particle with a diameter of 670 μm and a density of 1474 kg · m^-3 was used as solid material. Computational procedures were performed in the platform of CFX4.4, a commercial CFD software package, by integrating the user-defined Fortran subroutines. The numerical results showed that the voidage contour of 0.8 was suitable to determine the jet boundary, and the jet penetration depth increased with increasing jet gas velocity or slit size. The effect of annular gas velocity （uc） on jet penetration depth was divided into three stages. （1） Jet penetration depth increased when uc increased from zero to the minimum fluidization velocity （cmf）; （2） At uc = umf, jet penetration depth reached its maximum; （3） Jet penetration depth then decreased with increasing uc although this tendency became weak when uc was greater than 2. 5Umf. Jet penetration depth decreased with increasing static bed height and this influence was more obvious when jet gas velocity was high.