溶湯処理プロセスにおける液中超音波の音場設計

抄録

Sound fields in liquids have been studied for effective utilization of ultrasonic energy in materials processing. Experimental conditions under which small particles could be concentrated by ultrasound were investigated using a cylindrical acrylic resin vessel filled with a 13 wt% aqueous sugar solution in which polystyrene particles of 0.24 mm diameter were initially dispersed uniformly. A distribution of acoustic pressure in the sound field was measured under the above one condition using a commercial ultrasonic meter (a calibrated hydrophone with a voltmeter). Another distribution of acoustic pressure in a copper vessel was also measured under the condition at the same driving frequency and liquid depth. It is clarified that the successful conditions for concentration of small particles are the resonant conditions of ultrasonic standing wave field and that the sound field is affected by vessel material used. A numerical scheme has been developed on the basis of the finite difference solution of the linear wave equation. The scheme allows us to design sound fields considering material and thickness of a vessel, depth and properties of a liquid, and a dimension and arrangement of a transducer at various driving frequencies. The calculated pressure distributions agreed well with the measured ones. These results may be useful to design ultrasonic fields in such materials processing as suppression of thermal convection, separation of inclusions and directional control of reinforcing fibers in composite.