Microfeeding with different ultrasonic nozzle designs.

Microfeeding of dry powder excited by ultrasonic vibration makes use of relatively simple equipment and can be applied to solid freeforming and pharmaceutical dosing. The nozzle was a vertical glass capillary and four configurations for ultrasonic actuation were investigated: Type I had a piezoelectric transducer ring bonded to the base of a cylindrical water-containing vessel containing an axial nozzle; Type II had a piezoelectric transducer ring attached to the sidewall of the vessel; Type III used direct mechanical connection to the glass wall of the capillary to give nominally longitudinal vibration; and Type IV also used direct connection to the glass tube but arranged to give progressive wave vibration. The experimental results show that all four configurations realized powder microfeeding and dosing but the characteristics, in terms of minimum flow rate, dependence on voltage amplitude and uniformity of dose varied considerably. The discharge of particles was observed by a high-speed camera.