细颗粒物声波团聚的微观机理研究

为拓展声波团聚机理，对声波团聚过程中的声流与声涡作用进行了理论和实验研究。利用声流测试系统，发现在0～1 kHz低频与5 kHz高频时，团聚室内声流现象较为明显；并通过可视化测试，在7 kHz高频时观察到明显的漩涡。结果表明，流场中的声流与声涡对颗粒团聚会产生很大的影响，声流或声涡越强，团聚效果越好。在0～1 kHz低频与5 kHz高频时，声流产生的切应力带动气溶胶颗粒发生碰撞团聚；高频时声涡力矩较大，其产生的轨道角动量带动粒子发生圆周和自旋运动；当声压级大于132 dB时，声涡团聚开始发挥作用，与声流一起促进颗粒团聚，且声压级越大团聚效果越强；与波节相比，波腹处的声流速度更大，声涡现象更明显，团聚效果也更好。

Research on micro-mechanism of acoustic agglomeration of fine particles

In order to broaden the mechanism of acoustic agglomeration, the interaction of acoustic streaming and vortex in the process of acoustic agglomeration of fine particles is studied theoretically and experimentally. The phenomenon of acoustic streaming is significant at the frequencies of 0~1 kHz and 5 kHz. Moreover, an obvious vortex is observed with the visualizing test at the high frequency of 7 kHz. It is found that the acoustic streaming and vortex of flow field have a great influence on acoustic agglomeration, the higher the intensity of acoustic streaming or vortex, the better the agglomeration effect. At 0~1 kHz and 5 kHz, the shear stress generated by acoustic streaming drives the aerosol particles to collide and agglomerate. At high frequencies, the sound vortex torque is relatively large, and the resulting orbital angular momentum drives the particles to undergo circular and spin motion, which promotes particle agglomeration. The experimental results show that the sound vortex agglomeration starts working together with the acoustic streaming to promote particle agglomeration when the sound pressure level is greater than 132 dB; and by increasing sound pressure level, the agglomeration effect can be enhanced and the velocity of acoustic streaming at wave loop is faster than that at wave node, which leads to more pronounced vortex phenomenon and better agglomeration effect.