Dynamics of bubbles in sound fields at low temperatures



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A review is given of previous knowledge of bubble dynamics in normal and quantum liquids. An experimental investigation of the dynamics of bubbles in water, liquid nitrogen, liquid helium I and liquid helium II has been conducted by optical and acoustical means. The optical studies consisted of the making of high speed movie pictures (3,000 frames/s) of visible cavitation in liquid helium I (Regime C) and in liquid helium II (Regime A) Cavitation was induced by means of a plane wave system in water and a cylindrical wave system in liquid nitrogen and liquid helium. The noise produced by cavitation has been analyzed and typical examples of the spectrum are shown, together with a summary of the line spectra in all three liquids. A more detailed study was carried out for the half-frequency response present in the cavitation noise spectrum. This consisted of discrete measurements of its variation with the driving voltage, temperature and static pressure. Chart recordings of the ambient sound pressure level were taken in liquid helium and liquid nitrogen to determine possible correlations between the audible cavitation threshold, the first harmonic response, the half-frequency response and the background noise. The results of the present investigation are discussed in the light of existing theories and special attention is devoted to the effects of the unusual thermal transport mechanism in liquid helium II.



Fluid dynamics, Bubbles, Dynamics, Low temperature engineering