VISUALIZATION OF ACOUSTIC PARTICLE INTERACTION AND AGGLOMERATION - THEORY EVALUATION

In this paper experimentally observed trajectories of particles underg oing acoustically induced interaction and agglomeration processes are compared to and validated with numerically generated trajectories base d on existing agglomeration theories. Models for orthokinetic, scatter ing, mutual radiation pressure, and hydrodynamic particle interaction are considered in the analysis. The characteristic features of the cla ssical orthokinetic agglomeration hypothesis, such as collision proces ses and agglomerations due to the relative entrainment motion, are not observed in the digital images. The measured entrainment rates of the particles are found to be consistently lower than the theoretically p redicted values. Some of the experiments reveal certain characteristic s which may possibly be related to mutual scattering interaction. The study's most significant discovery is the so-called tuning fork agglom eration [T. L. Hoffmann and G. H. Koopmann, J. Acoust. Sec. Am. 99, 21 30-2141 (1996)]. It is shown that this phenomenon contradicts the theo ries for mutual scattering interaction and mutual radiation pressure i nteraction, but agrees with the acoustic wake effect model in its intr insic feature of attraction between particles aligned along the acoust ic axis. A model by Dianov et al. [Sov. Phys. Acoust. 13 (3), 314-319 (1968)] is used to describe this effect based on asymmetric flow field s around particles under Oseen flow conditions. It is concluded that t his model is consistent with the general characteristics of the tuning fork agglomerations, but lacks certain refinements with respect to ac curate quantification of the effect. (C) 1997 Acoustical Society of Am erica.