MECHANISMS OF REMOVAL OF MICRON-SIZED PARTICLES BY HIGH-FREQUENCY ULTRASONIC-WAVES

In this paper, theories of particle removal by high-frequency ultrason ic waves are discussed and tested against recent experimental data, Fi rst, the principal adhesion forces such as van der Waals forces are br iefly reviewed and the typical uncertainties in their size in particle -surface systems are assessed, The different ultrasound-induced forces -linear forces such as added mass, drag, lift, and Basset forces and n onlinear ones due to radiation pressure, and drag exerted by acoustic streaming-are discussed and their magnitudes are evaluated for typical cleaning operations, It is shown that high-frequency ultrasound can c lean particles most effectively in media with properties like water be cause: (1) the wavelength can be made comparable to the particle radiu s to promote effective sound-particle interaction; (2) the viscous bou ndary layer is thin, minimizing particle ''hide-out;'' and (3) both th e added mass and radiation pressure forces exceed typical adhesion for ces at high frequencies, Based on these analyses, possible mechanisms of particle removal are discussed and interpreted in terms of experime ntal observations of particle cleaning.