The role of acoustic cavitation in liquid pressurization in narrow tubes

The liquid pressurization mechanism in narrow tubes as a result of high intensity ultrasonic field along the irradiation direction is discussed, with a focus on the physical behavior of acoustic cavitation bubbles formed at the tubes open end. The acoustic energy dissipated at the surface of the bubbles results in radiation pressure with a second harmonic frequency (2f). We show here that during the phenomenon, which resembles the functioning an ultrasonic pump, cyclical pressure fluctuations with the second harmonic frequency 2f are observed using a high-response pressure transducer. The maximum value of accumulating pressure is equivalent to the positive peak of the sound pressure in the tube without acoustic cavitation. It can be thought that the cyclic collapse and expansion of acoustic cavitation bubbles at the tubes open end contribute to the control of the inrushing sound pressure. In particular, the transmission behavior of the received pressure in a viscous liquid containing gas bubbles with high number density near the tubes open end (a quantity that is related to the kinematic viscosity of the medium liquid) plays an important role in this pressure accumulation mechanism. A dynamic model of this pressurization phenomenon is also discussed.