MadSci Network: Physics

Re: is there relationship between the Hz of an Ultrasonic pulse and bubble size

Date: Wed Sep 29 06:36:06 2004
Posted By: Sean Hunt, Secondary School Teacher, Science, ISM
Area of science: Physics
ID: 1094110425.Ph

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 for more detail.

Sean Hunt

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