Effects of Ultrasound on Behavior of Fine Solid Particles in Solid-liquid Mixture (1st Report, Horizontal Irradiation in Stationary Solid-liquid Mixture)

Abstract

Separation of particles or decreasing the particle concentration in a solid-liquid two-phase flow is desired. Utilization of ultrasound has been considered as an alternative technique for the separation of particles. It is known that particles are aggregated by the radiation pressure of ultrasound. However, the effect of ultrasound with cavitation on particle behavior is not well known. Thus, water with aluminum particles having a density of 2720 kg/m3 and diameters of 50 to 150μm or smaller aluminum powder in a rectangular vessel was horizontally irradiated by ultrasound with frequencies of 23 kHz or 100 kHz, and a standing wave was formed. The following results were obtained. For ultrasound with 100 kHz, the aluminum powder aggregated in vertical lines. For ultrasound with 23 kHz and acoustic cavitation, we noticed that the aluminum particles were gathered at points near antinodes of the sound pressure profile because of flow induced by acoustic cavitation. When the particles were provided continuously with relatively high concentration, particle clumps formed and remained. Then, the particle clumps became larger and suddenly fell faster than the surrounding small particles. Such phenomena repeated. For relatively low concentration, particle clumps did not become large, and remained at the same positions.