Acoustic cavitation bubbles ultrasonic frequency

Fig. 1.1 The regions for transient cavitation bubbles and stable cavitation bubbles when they are defined by the shape stability of bubbles in the parameter space of ambient bubble radius (R0) and the acoustic amplitude (p ). The ultrasonic frequency is 515 kHz. The thickest line is the border between the region for stable cavitation bubbles and that for transient ones. The type of bubble pulsation has been indicated by the frequency spectrum of acoustic cavitation noise such as nf0 (periodic pulsation with the acoustic period), nfo/2 (doubled acoustic period), nf0/4 (quadrupled acoustic period), and chaotic (non-periodic pulsation). Any transient cavitation bubbles result in the broad-band noise due to the temporal fluctuation in the number of bubbles. Reprinted from Ultrasonics Sonochemistry, vol. 17, K.Yasui, T.Tuziuti, J. Lee, T.Kozuka, A.Towata, and Y. Iida, Numerical simulations of acoustic cavitation noise with the temporal fluctuation in the number of bubbles, pp. 460-472, Copyright (2010), with permission from Elsevier...

The technique of a cavitation noise measurement is the basis for the methods of determination of the cavitation threshold [31]. It is well known that the occurrence of cavitation phenomena in liquid—formation and collapse of a large quantity of bubbles of different sizes which have their own resonance frequencies—results in radiation of white acoustic noise. Separate frequency peaks corresponding to resonance frequencies and subharmonics of cavitation bubbles being added together with frequency tones from other cavitation bubbles produce a spectrogram of noises quantitatively different from that of the base tone of the carrier ultrasonic frequency which is used during the current US treatment. 

Figure 2. Experimental apparatus for the investigations of acoustic cavitation in a liquid metal. (1) Signal-Generator (2) Amplifier (3) Ultrasonic Generator (4) Transducer (5) Frequency meter (6) Valve voltmeter (7) Sensor of a waveguide stick (8) Recorder (9) Cavitometer (10) Potentiometer (11) Probe (12) Crucible with a melt (13) Source of ultrasound (14) Receiving stick (15) Electric furnace (16) Detector of the first bubble.

The bubble-dynamics equations are very similar to acoustic cavitation the only difference being the fact that the surrounding fluctuating pressure field is driven by hydrodynamic conditions existing downstream of the constriction, whereas in the case of acoustic cavitation, it is dependent on the frequency and intensity of the ultrasonic irradiation (sinusoidal variation). There are two approaches used for the estimation of the local pressure at any location downstream of the constriction (the typical pressure recovery profiles are shown in Fig. 8.2.6). 

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