Influence of the acoustic entrainment on aerosol particle interactions: experimental balance of the hydrodynamic mechanisms

A new experimental micro-scale study of particle interactions acoustically induced in monodisperse aerosols is presented in this work. It is devoted to the study of the influence exerted by the acoustic entrainment experienced by the single particles on their attraction processes and, in particular, on the hydrodynamic mechanisms that govern them. Glass spheres with certified diameters of 8.0 ± 0.9 μm immersed in air as dilute aerosols were subjected to homogeneous plane standing waves with a constant velocity amplitude U0 = 0.44 m/s at diverse frequencies, ranging from 200 Hz up to 5 kHz, at which the particles were much smaller than the respective acoustic wave-lengths.

The experiments were carried out in the viscous forces domain with respect to the inertial forces, at a constant Reynolds number Re=0.24, in an emerging Oseen regime with very weak asymmetries in the flow field. For the first time this paper presents a complete collection of particle interactions at acoustic entrainments varying from qp=0.84 to qp =0.05, i.e., covering practically its complete range of variability.

It is experimentally confirmed for the first time the presence of the mutual radiation pressure as a disturbing effect on the acoustic agglomeration generated on the aerosols, that is produced by the acoustic wake effect. Our results coincide with other previous researchs, agreeing with the theoretical prediction.