|MadSci Network: Physics|
Ray, Cavitation—the formation of bubbles—is a familiar phenomenon. Whenever a liquid is agitated violently, there is a possibility that cavitation will occur In the case of boat propellers or hydraulic machines, cavitation is a problem that engineers try to avoid. In other contexts, however, cavitation can be useful—as, for example, in ultrasonic cleaning devices. Desirable or not, cavitation is a complex phenomenon because inhomogeneities in the liquid—such as walls, dissolved gases, vortices, and impurities—usually play a major role in the nucleation of bubbles. As a consequence, our understanding of cavitation is incomplete. (taken from PhysicsToday, -- Humphrey Maris and Sebastien Balibar) When sound enters water it forms a complicated array of waves that may cause localised increases and decreases in pressure. At the low pressure points the water is stretched and can overcome an energy barrier (the spinodal limit) in order to form a bubble. It would seem to me that at high frequencies the likelihood of a bubble forming will be at its greatest, as would an increase in amplitude. Unfortunately the chaotic nature of the system implies a breakdown (or disruption) of bubbles by interference thus higher frequencies would see many smaller short lived bubbles and lower frequencies would see fewer yet larger and longer lived bubbles. Check out http://www.aip.org/pt/feb00/maris.htm for more detail. Sean Hunt
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