Acoustic separation in a laminar flow

Preliminary observations gathered using a plane ultrasonic wave field interacting with water suspended fibers circulating in a channel flow have indicated that the acoustic radiation force could be used to separate fibers into two or more fractions based on fiber radius. The continuous process relies on the use of a wall-mounted, rectangular cross-section piezoelectric ceramic transducer to selectively deflect flowing fibers as they penetrate the ultrasonic field. The transducer´s frequency is 150 kHz. Depending upon the amount of dissolved gas in water, separation is obtained using a standing or traveling wave field. A description of the experimental setup is presented. Results obtained using rayon fibers and reclaimed wood pulp fibers at consistencies up to 1%. and at flow velocities up to 12.5 cm/s (Reynolds numbers up to 2500) are reported. Possible applications of the separation concept in the pulp and paper industry are discussed