Abstract
Ultrasound techniques are applied in various fields such as washing, fine particle manipulation and solid-liquid separation. In the fine particle manipulation, ultrasonic ranging in MHz band is usually employed. Fine particles with μm order in diameter are treated because of limitations of the wavelength. In contrast, we discovered phenomena that mm-order particles dispersed in water are flocculated spherically by irradiating 20-kHz-band-ultrasound. In order to clarify the mechanism of this flocculation, we investigated the sound pressure profiles in the vessel, and the positions and diameters of the flocculated particle swarm, varying the water depth, ultrasound frequency and particle diameter. From these results, the particle swarm was trapped in the anti-node of the standing wave. The diameter of the particle swarm was dramatically changed by subtle control of the frequency. Based on these results, we will propose a new technique capturing and separating sub mm- or mm-order particles by their diameter.
