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Word Data Modules PowerPoint Data Modules Excel Data Modules Access Data Modules Some authors [70, 88] believe that the degassing of a liquid is possible only when cavitation is present, after the formation of vapor-gas cavities, which, increasing in size due to diffusion and coalescence, escape from the liquid. In the opinion of others [72] degassing has nothing to do with cavitation, but is determined by the diffusion of gas into pulsating bubbles already present in the liquid and their subsequent coalescence.

If this problem is to be resolved unequivocally, we must compare the kinetics of the degassing process at low enough acoustic intensities that cavitation is clearly absent, as well as in the presence of cavitation. Of decisive interest in this connection is the report in [93] of the existence of an optimum range of intensities for degassing, within which the rate of change of the gas concentration is a maximum. This range is limited at the low-intensity end by the cavitation threshold.

The authors ascribe the concurrent onset of cavitation and increase in the mass-transfer rate to the action of two factors: 1 an increase in the number of bubble nuclei due to the formation and detachment of microbubbles from the surface of the extant bubbles by the excitation of large-amplitude surface modes; 2 an increase in the diffusion flow of gas into the bubbles due to the increase in the interface area when the bubbles oscillate in higher modes.

The striking feature of the effect was the fact that the shape of the resulting cavity very precisely emulated the contour of the emitter tip. The technique was rapidly exploited in industry, and during — several countries had begun the manufacture of industrial prototypes of ultrasonic machine tools. Unable to display preview.

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