Ultrasound conditioning of suspensions – studies of streaming influence on particle aggregation on a lab- and pilot-plant scale

Abstract

Suspension conditioning by ultrasound induced particle aggregation in a 3.3 MHz standing wave field was investigated in lab- and pilot scale sedimentation reactors (sonicated volume approx. 375 ml and 10 l). These were equipped with a variable number of acoustically transparent film (ATF) elements, inserted perpendicular to the sound propagation direction. ATFs control the development of undesired large-range Eckart-type acoustic streaming and thermal convection. ATF insertion led to increased separation efficiency especially for particles smaller than 10 μm. Results with a varied geometric set-up indicate the existence of an optimum for the number of ATFs inserted. Optical investigation of particle behaviour in different pilot plant configurations showed reduced streaming within the divided 24 mm pathlength sonic chamber, whereas at 100 mm pathlength, turbulent streaming dominated.