湍动流化床过渡段中颗粒速度分布的光纤测量与模拟

Particle Velocity Measurements in Transition Section of Turbulent Fluidized Beds Using Optical Fiber Probe and CFD Simulation

流化床中颗粒速度的测量一直是个技术上的难点。今针对光纤测量信号提出一种基于互相关原理的时均速度计算方法。考虑到数据分段计算时其可靠性方面的差异,将互相关系数作为第二权重因子引入时均速度计算公式。利用PV6D光纤探针在200 mm直径流化床中测得的原始信号,对比了三种数据处理方法所得的颗粒时均速度,并分别计算其床层截面颗粒净流率,说明提出的方法可靠性更高。据此测量了流化床过渡段不同高度处颗粒时均速度的径向分布,并采用修正的三段曳力模型来描述具有团聚行为的颗粒曳力,进行计算流体力学模拟。测量与模拟结果均表明,从过渡段到稀相段,床中心区的颗粒速度先降低后升高,其径向分布也从陡峭变平缓,然后再次趋于陡峭。颗粒速度分布的上述规律主要由固含率与气速的径向分布共同作用所致。

Measurement of particle velocity in fluidized beds is always technically difficult. A new method based on cross-correlation principle was proposed to calculate time-averaged velocity of particles. Considering the different reliabilities of signal segments, a cross-correlation coefficient was introduced into the formula for calculating time-averaged velocity. A PV6D optical fiber probe was used to obtain original signals in a fluidized bed with 200 mm i.d., and the time-averaged velocities calculated from three different methods were compared. The calculated particle volume flow rates based on different velocity calculating methods indicate that the method proposed in this paper is more reliable. Based on this method, particle time-averaged velocity was measured at different heights in the transition section of a turbulent fluidized bed. A modified three-zone drag law model was used to predict the flow structure of particles with clustering behavior. The experimental and simulation results both indicate that, from the transition section to the dilute section, particle velocity of the core region rises at first and then declines, the radial velocity distribution changes from a steep curve to a flat one, and then becomes steep again. This result depends on both solid concentration distribution and gas velocity distribution.