Transient cavitation in high-quality-factor resonators at high static pressures

Abstract

It is well known that cavitation collapse can generate intense concentrations of mechanical energy, sufficient to erode even the hardest metals and to generate light emissions visible to the naked eye [sonoluminescence (SL)]. Considerable attention has been devoted to the phenomenon of "single bubble sonoluminescence" (SBSL) in which a single stable cavitation bubble radiates light flashes each and every acoustic cycle. Most of these studies involve acoustic resonators in which the ambient pressure is near 0.1 MPa (1 bar), and with acoustic driving pressures on the order of 0.1 MPa. This study describes a high-quality factor, spherical resonator capable of achieving acoustic cavitation at ambient pressures in excess of 30 MPa (300 bars). This system generates bursts of violent inertial cavitation events lasting only a few milliseconds (hundreds of acoustic cycles), in contrast with the repetitive cavitation events (lasting several minutes) observed in SBSL; accordingly, these events are described as "inertial transient cavitation." Cavitation observed in this high pressure resonator is characterized by flashes of light with intensities up to 1000 times brighter than SBSL flashes, as well as spherical shock waves with amplitudes exceeding 30 MPa at the resonator wall. Both SL and shock amplitudes increase with static pressure.

Sonoluminescence: Experiments and models (Review)

“…Within the first acoustic cycle in the experiment with the water-water vapor system [121], under the experimental conditions f a = 26 kHz, Т l = 20°С, and p st = 100 atm, nucleation of a bubble, its expansion to R m ≈ 0.5 mm, its collapse, and SW in the liquid were observed. The SW amplitude measured at distance r = 1 cm from the bubble center was ~1 kbar.…”

“…In this device, bub ble oscillations only persist for several hundreds of cycles. In [121], this type of cavitation was called tran sient cavitation to distinguish it from SBSL, where the bubble lifetime is much longer.…”

“…In [121], the authors describe a high quality spherical resonator that allowed studies at a static pressure of up to 300 bar. The resonator was made from stainless steel with an inner diameter of 203 mm and a wall thickness of 0.55 mm.…”

“…Experimental studies of SL and shock waves that form in the resonator were carried out [121,122]. Within the first acoustic cycle in the experiment with the water-water vapor system [121], under the experimental conditions f a = 26 kHz, Т l = 20°С, and p st = 100 atm, nucleation of a bubble, its expansion to R m ≈ 0.5 mm, its collapse, and SW in the liquid were observed.…”

Enhancing the aggressive intensity of hydrodynamic cavitation through a Venturi tube by increasing the pressure in the region where the bubbles collapse

“…10 A system to generate acoustic cavitation at ambient pressures in excess of 30 MPa has been developed. 11 However, some studies have reported that the intensity of hydrodynamic cavitation could be increased with less energy compared with that required for acoustic cavitation. 12 In practical applications for chemical reactors, such as water treatment systems, hydrodynamic cavitation is preferable to acoustic cavitation, as it can be easily scaled up to enhance its aggressive intensity, and acoustic cavitation, moreover, has not been applied to large scale operations because of the difficulties in scaling up ultrasonic reactors.…”