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Some experimental findings on the dynamics of vapor bubbles in ultrasonic fields are reviewed. In particular, attention is drawn to a phenomenon which might be described as ultrasonically stimulated boiling. There is also a summary of certain pertinent facts about the threshold of cavitation in liquids with low foreign gas content, such as liquid nitrogen or liquid helium. It is emphasized that threshold pressure amplitudes can be less than the static pressure. It is proposed that an explanation of these observations could lie in a net positive heat transfer into a pulsating bubble. The minimum amplitude required to cause such a ‘‘rectified’’ heat transfer is calculated.

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The equations governing the motion of vapor bubbles in a sound field were formulated earlier [R. D. Finch and E. A. Neppiras, J. Acoust. Soc. Am. 53, 1402–1410 (1973)], and linear oscillatory solutions of the equations were obtained. Nonlinear solutions have now been obtained, using a numerical method, and some typical results will be presented. Some of these results are in accordance with the linear oscillatory solutions but some are not. These nonoscillatory solutions can be associated with an exponential type of linear solution. Both collapse and growth of an exponential nature are predicted.