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.