气固搅拌流化床内压力脉动特性的数值模拟

在传统气固流化床中引入搅拌桨,可减轻聚合物颗粒的黏附并强化流态化过程。采用计算流体力学(CFD)方法对搅拌流化床内的压力脉动特性进行数值模拟,考察流态化过程中的气泡行为。模拟过程采用多重参考坐标系方法解决搅拌桨区域的运动问题,由欧拉双流体模型和颗粒动力学方法模拟气固两相流。床层压力脉动的统计分析和功率谱分析表明,随着搅拌桨转速的增加,流化床内的压力脉动标准偏差和功率谱幅值变小,床层内的平均气泡尺寸减小,床层可由鼓泡流态化向散式流态化转变。

Numerical simulation of pressure fluctuation in gas-solids agitated fluidized bed

Agitators were introduced to gas-solids fluidized beds to improve fluidization performance and scrape sticky particles from internal bed wall.Numerical simulations based on the computational fluid dynamics (CFD) method were carried out to predict bubble behavior in the agitated fluidized bed.The Euler-Euler two-fluid model and the kinetic theory of granular flow were incorporated to describe the gas-solids flow, whist the multiple reference frame method was applied to deal with the rotation of agitator.The numerical models were validated by bed pressure drop and its fluctuation obtained in the experiment.The bubble behavior and fluidization performance were investigated in terms of pressure fluctuation.The results indicated that the amplitudes of pressure fluctuation and its power spectrum were reduced by increasing agitation speed of frame impeller, while dominating frequency had positive but inconspicuous correlation with agitation.The characteristics of pressure fluctuation showed that bubble size in the fluidized bed went down with a rise in agitation speed, which might lead to the transition from bubbling fluidization to particulate fluidization.