液固流化床内床层动态特性的CFD模拟

在对液固流化床内流动特性进行理论分析的基础上，采用多相流CFD方法模拟了二维矩形流化床内水和玻璃球体系的流体动力学特性。实验结果表明，流体速度突变后，液固流化床从一个平衡状态向另一个平衡状态过渡。当液体速度减小时，床层表面及分隔界面的变化与理论模型预测一致；由于重力不稳定性的影响，当液体速度增大时，床层表面稳定上升但与时间不呈线性关系，且分隔界面难以分辨。进而膨胀后停留时间的长短对收缩过程的影响也可以忽略。尽管床层收缩时间明显小于实际膨胀时间，但是与预报的理想膨胀时间比较接近。模拟结果与前人的实验研究和理论分析相吻合，表明多相流CFD模拟可以很好地预测液固流化床的床层动态行为。

CFD simulation for the kinematic characteristics of liquid-solid flow in fluidized beds

The contracting and expanding processes of liquid-solid flow have been analyzed theoretically and simulated numerically in a two-dimensional fluidized bed using the commercial Computational Fluid Dynamics(CFD) code,CFX4.4 with water and glass beads as the liquid and solid phases.A liquid-solid bed in equilibrium would transfer to a new equilibrium state after the liquid flux changes greatly.When the liquid flux is suddenly decreased,the bed is divided distinctly into two zones: an upper zone and a lower zone.The liquid volume fraction keeps the original value at the upper zone,whilst the liquid volume fraction becomes a new value corresponding to the new liquid flux.In fact,there exists a narrow region between the above two zones,which can be regarded as the "internal interface".Bed surface and internal interface change linearly with the simulated time although the bed surface and internal interface moved downwards and upwards,respectively.When the liquid flux is suddenly increased,both the bed surface and internal interface rising with time are in nonlinear form,which is attributed to an influence of the gravitational instability.However,the effect of the simulated period of the expansion process on the response time of the contracting process can be neglected.The idealized expansion response time is close to the contraction response time,which is far shorter than the simulated value.All simulated data are in fair agreement with the theoretic and experimental data reported by other researchers.