Investigation of Acoustic Cavitation Energy in Ultrasonic Tanks

Acoustic cavitations are produced when ultrasound is coupled with liquid medium and the cavitation energy released is a characteristic feature of frequency of ultrasound used, apart from properties of the medium. Cavitation implosions play a major role in all ultrasound-assisted processes, and hence, characterization of cavitation energy in ultrasonic tanks is an important aspect. This paper presents the cavitation energy measurements made within ultrasonic tanks operating in the frequency range of 33 kHz to 470 kHz. Cavitation energy is very high in low frequency fields and it decays with frequency, following an inverse cubic relation. Increase in viscosity and decrease in surface tension of the liquid medium results in reduced cavitation intensities. The effect of hydrostatic pressure on cavitation energy was also studied. When hydrostatic pressure was increased, cavitation energy increases initially, upto 2 atm pressure (absolute), and then it decreases with pressure at constant power input of 500 W. Higher frequencies (>400 kHz) deliver less cavitational energy, which is optimal for processes such as cleaning of delicate parts, and ultrasound-assisted bio-processes.