液固循环流化床中颗粒轴向速度的实验研究

Study on the Axial Velocity of Particles in a Liquid-Solid Circulating Fluidized Bed Using the Ultrasound-Doppler Technique

利用超声多普勒测速仪实验测量了液固循环流化床中不同径向位置处颗粒瞬态轴向速度,研究了其概率密度分布特征。采用瞬态速度的标准偏差衡量瞬态速度的波动程度,考察了不同操作形式下的颗粒时均轴向速度的径向分布以及表观液速和颗粒循环速率等操作条件对速度波动程度和速度均值径向分布的影响。利用相间作用力对两种分布的特点进行了机理分析,并对液固和气固循环流化床中颗粒的流动行为进行了比较。

The ultrasound Doppler velocimetry (UDV) was used to investigate the transient axial velocity of particles and its time-averaged behaviors in a liquid-solid circulating fluidized bed. The standard deviation was used to scale the fluctuation of the transient axial velocities of particles. The experimental results showed that the radial profile of the mean axial velocity of particles under the circulating fluidization is considerably different from that without circulation. With the increase of superficial liquid velocity, the fluctuation of transient velocities decreases, and the mean axial velocity of particles increases approximately linearly in the core region and does not vary considerably in the wall region. With the increase of particle circulating rate, the fluctuation of transient velocities decreases first and then increases, and the mean axial particle velocity increases first and then reaches a saturation profile. The comparison of the probability distribution of the transient velocities and radial profile of the mean velocity with GSCFB confirmed that the particles are homogeneously dispersed in the liquid.