Sonothickening: Continuous In-line Concentration/Clarification of Fine Particle Suspensions by Power Ultrasound

Abstract

A novel technique has been developed for the concentration of fine particle suspensions based on the transient response of particles smaller than 10 μm to ultrasound. Sonically induced particle velocities have been measured and magnitudes of the sonic forces acting on a particle in a suspension calculated over a range of particle sizes, sound frequencies, sound intensities and suspension concentrations. Particle velocities of up to about 12 ms−1 were obtained at the sonic transducer tip when the particle size is approximately 1 μm. The solid phase of the suspension acquired a higher velocity than the continuous liquid phase, facilitating velocity difference as the mechanism of concentration. An in line concentrator for suspensions was designed, utilizing this relative velocity and the trajectory deviation of the particles in the acoustic field. Using the novel concentrator it has been demonstrated that the concentration of suspensions could be increased by up to 50% in a single pass through the radiation field. Power intensities between 40 and 60 W cm−2 achieved the highest increases of suspension concentration. Operating and design variables such as feed velocity, feed concentration, particle size, ultrasonic intensity and frequency were investigated experimentally.