Abstract:

In the Euler-Lagrange coordinate system, mixing characteristics of particles in a single jet fluidized bed were studied with discrete element method. A mixing index was introduced to quantitatively analyze axial and radial mixing quality in the bed, as well as to investigate influnce of superficial gas velocity and spring constant on mixing charcteristics. The simulation provided sequence diagrams of axial and radial mixing, distributions of gas and particle velocities, and mixing index distributions of particles across the bed at various parameter settings. The results showed that particle mixing process in the bed was determined by capacity of particle circulation and diffusion. Axial mixing rate was mainly controlled by internal circulation speed of particles, whereas radial mixing rate was mainly controlled by particle diffusion capacity. With the increase of superficial gas velocity, the internal circulation speed of particles was enhanced and thus axial mixing process was accelerated but radial mixing was weakly influenced. When spring constant was increased, both mixing speed and quality of particles were decreased as well as radial mixing process was less affected than that axial mixing by spring constant.

Key words: fluidized bed, particle, mixing, mixing index, quantitative evaluation, numerical simulation

摘要：

在欧拉-拉格朗日坐标系下，采用离散单元法对单孔射流流化床内颗粒混合特性进行了数值模拟。引入混合指数对床内轴向及径向布置的颗粒混合质量进行定量分析，并研究了不同表观气速、不同弹性系数对颗粒混合特性的影响。模拟得到了颗粒轴向及径向混合序列图、气体和颗粒速度分布、整床颗粒混合指数分布、参量变化时整床颗粒混合指数分布。结果表明：流化床床层内颗粒混合速度受颗粒内循环能力和颗粒扩散能力的综合作用。单口射流喷动流化床颗粒轴向混合速度主要由颗粒内循环速度决定，颗粒径向混合速度主要由颗粒扩散能力决定。表观气速增大时，颗粒内循环速度增加，从而加快了颗粒轴向混合进程，但对颗粒径向混合影响微弱；弹性系数增大时，颗粒混合速度及混合质量均下降，并且弹性系数增大对颗粒径向混合进程影响小于颗粒轴向混合。

关键词: 流化床, 颗粒, 混合, 混合指数, 定量评价, 数值模拟