燃煤细颗粒和颗粒团动力学特性的比较

为研究颗粒团的动力学特性，利用可视化技术对声波场中颗粒和颗粒团的声波夹带进行了实验研究。在相同的实验条件下，拍摄到大颗粒团和小颗粒的声波夹带位移振幅分别为12.6 mm 和12.5 mm，相对应的张驰时间比约为1；用扫描电镜观测低压电称冲击器(ELPI)收集到的颗粒和颗粒团，发现在同一级收集盘上，能收集到较大的颗粒团和较小的颗粒，再次证明了大颗粒团和相应的小颗粒具有相近的空气动力学特性。利用颗粒团的分形特性对可视化实验中颗粒团的声波夹带进行理论分析，计算得到实验中观测到的颗粒团和颗粒的张驰时间比为1.03，与实验结果吻合。这说明与相同质量的单颗粒相比，具有分形体特征的颗粒团的气流跟随性被增强，可能不利于利用惯性分离的方法脱除气流中的颗粒团。

Comparison of Dynamical Behavior Between Fine Particles and Aggregates From Coal Combustion

In order to study the dynamic behavior of the aggregates, the acoustic entrainments of a particle aggregate and a single particle were studied and compared by means of visualization technology. The trajectories of the aggregate and the particle in an acoustic field showed that the vibration amplitudes of the aggregate with a larger projected size and the smaller single particle were 12.6μm and 12.5μm under the same condition, respectively. It means that the ratio of the relaxation times of the aggregate to the particle was about 1.0. According to the SEM photo of the particle morphology on the impact plate of ELPI, it was also found that bigger aggregates and smaller single particles were both collected at the same stage of the ELPI, which testified both of them have similar dynamic behaviors once again. Furthermore, considering the fractal structure of the aggregate in the theoretical calculation of the acoustic entrainments of the aggregate and the particle, the calculated relaxation time ratio between them was 1.03, which was consistent with the value derived from the experiment. Thus, comparing with a particle that has identical mass, a fractal aggregate is more prone to be entrained, which might be unfavorable to the inertial removal of the aggregates suspended in gas.