The dynamics of vapor bubbles in acoustic pressure fields

In spite of a superficial similarity with gas bubbles, the intimate couplin g between dynamical and thermal processes confers to oscillating vapor bubb les some unique characteristics. This paper examines numerically the validi ty of some asymptotic-theory predictions such as the existence of two reson ant radii and a limit size for a given sound amplitude and frequency. It is found that a small vapor bubble in a sound field of sufficient amplitude g rows quickly through resonance and continues to grow thereafter at a very s low rate, seemingly indefinitely. Resonance phenomena therefore play a role for a few cycles at most, and reaching a limit size-if one exists at all-i s found to require far more than several tens of thousands of cycles. It is also found that some small bubbles may grow or collapse depending on the p hase of the sound field. The model accounts in detail for the thermo-fluid- mechanic processes in the vapor. In the second part of the paper, an approx imate formulation valid for bubbles small with respect to the thermal penet ration length in the vapor is derived and its accuracy examined. The presen t findings have implications for acoustically enhanced boiling heat transfe r and other special applications such as boiling in microgravity. (C) 1999 American Institute of Physics. [S1070-6631(99)02208-4].