Talk:Cavitation

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[edit] Factual inaccuracy

The following statement seems untrue to me:

In order for cavitation to occur, the cavitation "bubbles" need a surface on which to nucleate. (emphasis added)

I would expect that while a nucleation surface subtantially lowers the nucleation energy required to create a cavity, it is not strictly required, and cavitation could occur spontaneously in a liquid with no impurities or local surfaces, if a higher nucleation energy is met. This seems analagous to the nucleation of crystals in a freezing liquid -- a crystal will typically form on a surface or at an impurity due to a lower nucleation energy, but absent that, crystals will form spontaneously if the liquid is supercooled.

Any experts care to comment?- Bantman 23:35, 12 January 2006 (UTC)

Hi Bantman

Indeed you are right, there exist two scenarios, one is termed "homogeneous cavitation" where you overcome the cohesive forces between the liquid molecules/atoms and the second "heterogeneous cavitation" where cavitation starts from some inhomogeneities. For water the homogeneous cavitation threshold is approximately -1.4kbar (number is correct!) which has been calculated and demonstrated experimentally. However, it is *very* difficult to have ultra-pure water which does not cavitate before the theoretical threshold. To my knowledge nobody was able to redo the experiments of Zheng et al. 1991. In contrast, the threshold on heterogeneous cavitation depends on the nuclei size, and can already start at a few tenth of a bar negative pressure.

Some references:

Homogeneous cavitation threshold: GREEN, J.L., DURBEN, D.J., WOLF, G.H. & ANGELL, C.A., 1990 Water and solutions at negative pressure: Raman spectroscopy study to -80 megapascals. Science 249, 649-652. ZHENG, Q., DURBEN, D.J., WOLF, G.H. & ANGELL, C.A., 1991 Liquids at large negative pressures: water at the homogeneous nucleation limit. Science 254, 829-832. BOTELER, J.M. & SUTHERLAND, G.T. 2004 Tensile failure of water due to shock wave interactions. J. Appl. Phys. 96, 6919-6924.

Stabilization of gaseous nuclei: FOX, F.E. & HERZFELD, K.F., 1954 Gas bubbles with organic skin as cavitation nuclei. J. Acoust. Soc. Am., 26, 984-989. HARVEY, E.N., BARNES, D.K., MCELROY, W.D. WHITELEY, A.H., PEASE, D.C. & COOPER, K.W., 1944 Bubble formation in animals. J. Cell Comp. Physiol. 24, 1-22.

Cavitation in dirty liquids: MADADNIA, J. & OWEN, I. 1993 Accelerated surface erosion by cavitating particulate-laden flows. Wear 165, 113-116.

[edit] Specious statement

By eliminating contact with water, and, therefore, eliminating the high drag of water, these torpedoes can move very fast underwater, perhaps even at supersonic speeds.

Seeing as the speed of sound in water is about 5300 km/hr, I think the last clause of that sentence is rather specious and detracts from the statement in general. After all, the Russians' Shkval torpedo can only travel at 370 km/hr.

Axda0002 16:39, 19 May 2006 (UTC)

There is indeed research going on, and small objects have been traveling with supersonic speed of the liquid in test channels. Some of the results are presented at conferences (not too much in open literature) and most of the spectacular experiments are confidential. One of the conferences where supercavitation is a topic are the regularly organized CAV symposia with the last one being held at Wageningen (The Netherlands) in 2006 (www.cav2006.com).