Talk:Cavitation/Archive 1

Archive 1

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.

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).(www.flightglobal.com)

Tunnels

The article gives a long "list of Cavitation tunnels" without giving any reference in the article on what a "Cavitation tunnel" even is. --Rehcsif (talk) 04:14, 23 March 2008 (UTC)

Lots of changes to this article since I wrote this, but no one has addressed (or commented on) this issue. I think it's a big flaw in the article. --Rehcsif (talk) 18:40, 31 March 2008 (UTC)

Liquid Energy

In section (Problems) what is "liquid energy", please elaborate or change to proper English. I hesitate to edit unless I am 100% sure of the edit. Suggest: energetic liquid energy stored in liquid

or something that does not allude to a new form of energy in liquid form.

Liquid Energy

In section (Problems) what is "liquid energy", please elaborate or change to proper English. I hesitate to edit unless I am 100% sure of the edit. Suggest: energetic liquid energy stored in liquid

or something that does not allude to a new form of energy in liquid form. 79.67.56.124 (talk) 02:51, 24 March 2008 (UTC)

Sonar or Hydrophonics

Perhaps this should be in sonar, but is reflected here.

I know the page on sonar covers the two under the same heading but; Correct me if I am wrong but SONAR uses a sound pulse to detect objects in liquids. Hydrophonics is the practice of underwater listening. —Preceding unsigned comment added by 79.67.56.124 (talk) 02:56, 24 March 2008 (UTC)

Discharge Cavitation

I feel that this section could be written to describe a more general phenomenon using laymen's terms. What, for example, is a "pump cutwater?"

Proper link?

In the introduction section, I linked the term "acoustic field" with our Sound article. I realize that there is an article on Underwater acoustics, but since the article term defines Cavitation as an occurrence with fluids, I've decided to link to the former instead. If anyone has any better ideas, feel free to make the change. --24.76.249.36 (talk) 20:13, 22 August 2008 (UTC)

Plant Cavitation

[my erroneous statement removed --HarryZilber (talk) 23:39, 10 April 2009 (UTC) ]

The explanation of Cavitation is hopelessly wrong.

Unfortunately it is wrong in many books also, specially if engineers trying to make physics. It is also wrong in written encyclopedias. I thought Wikipedia is a great opportunity to correct easily such mistakes, but Admins fight always for the wrong thing. It was hopeless in the german Wikipedia and probably there also.

“Cavitation is the formation of vapor bubbles of a flowing liquid…” it can not be more wrong. This happens if you cook water!

By the way: Cavitation has absolute nothing to do with bubbles, steam etc Since everything has a breaking point, Water get torn apart by great forces. Between the torn pieces is in the first microseconds nothing, no steam – simply a vacuum. It is a very fast process, much faster than steam can build up. The empty space can be called “cavity”. At the implosion of the cavity by the water pressure the surface energy of the cavity get concentrated at a very small point and heat this spot up that metal melts. The fluid metal is taking away by the mechanical Energy of the implosion and last by the water flow. The damage is done –as always – by a concentration of energy in space and time. The pictures of the damaged propellers are right; everything else is wrong. Engineers have never understood cavitation and it seem they are all together there. I find not a single reference to a physicist. He, it is a physical phenomenon! A hard boiled Physicist --Inventor 00:50, 26 November 2010 (UTC) www.InventorWolfhart.com —Preceding unsigned comment added by Inventor (talk • contribs) 00:50, 26 November 2010 (UTC)

Cavitation is nothing more than temporary of bubbles of vacuum created in a liquid or gas material. There, 1 sentence description. Patcat88 (talk) 22:45, 11 June 2011 (UTC)

I do not agree. It is not a vacuum, according to Fundamentals of Caviataion (Franc and Michel) and Cavitation and Bubble Dynamics (Brennen). Cavitation results in vapor bubbles in the fluid. Boiling and cavitation are both phenomena that result in water vapor, but boiling happens due to higher temperature, and cavitation happens due to lower pressure. Ehufsted (talk) 21:27, 27 June 2011 (UTC)

The vapor would not be there if there were no vacuum there. Patcat88 (talk) 15:29, 8 August 2011 (UTC)

In the first instance of the implosion causing the bubble there is an expanded vacuum, a bubble of nothing if you will. This is also evident with sonoluminescence, whilst I have no articles to cite backing this up my only knowledge on this subject is from physics, not engineering; thus I concur with the above statement that if we are citing engineering points of view on this subject then they are terribly wrong. BaSH PR0MPT (talk) 22:06, 23 June 2013 (UTC)

help

if anyone knows an equation to find how fast the "bubble" will calapse, that would be great. thanks. Jake1993811 (talk) 06:16, 28 December 2011 (UTC)

List of cavitation tunnels

The long "List of cavitation tunnels" interrupts the article flow and intereferes with reading the TOC smoothly. It should either be deleted, shifted off to a standalone page, or converted to a table. —DIV (138.194.11.244 (talk) 05:54, 19 July 2012 (UTC))

I agree. I've deleted the list, and added the link to water tunnels in the 'See Also' section. Artorius (talk) 03:46, 16 October 2012 (UTC)

Article quality

An excellent article for the interested reader. (talk) 01:13, 16 October 2012 (UTC)

Spellings

I have standardized on American spellings, although I am English. I found lots of -ize but no -ise and the number of vapors and vapours was roughly equal. Biscuittin (talk) 19:36, 14 March 2013 (UTC)

citation needed - solved?

"At the point of total collapse, the temperature of the vapor within the bubble may be several thousand kelvin, and the pressure several hundred atmospheres.[citation needed]"

http://www.newton.dep.anl.gov/askasci/phy00/phy00135.htm

Cavitation of water and Hydrogen Fuel

I've heard that water can be injected into a near vacuum environment and split into its component elements via cavitation by turbines. This has been proposed as a way to produce hydrogen fuel for cars. Is there anythig to this? Whether the answer is yes or no, this really should be noted in this article or in its own dedicated article, even if its just to debunk the myth.WertMooMoo (talk) 08:59, 28 May 2013 (UTC)

Cavitation modeling

If anyone knows anything about cavitation modelling, check out the main article to help improve it. --Iamozy (talk) 20:39, 23 June 2014 (UTC)

Vascular cavitation in plants -- clarifications/corrections?

The plant section describes the cavitation bubbles as "air" -- is this a mistake? It is water vapor, not air, correct?

It also describes the reintegration of the bubble into the water as "dissolving" -- is this accurate? Doesn't it just phase change back into water?

It also describes the cavitation as sometimes being "clearly audible". I read the citation (#31) and while I didn't read every word, I could not find supporting claims regarding sound. A youtube video on what I assume is the same phenomenon describes the sounds as ultrasonic: https://www.youtube.com/watch?v=uWL0EoZh09w, i.e. not audible.

Chconnor (talk) 06:23, 13 October 2014 (UTC)

@Chconnor:. Good questions! I wrote that section from various lecture notes about 5 years ago and unforuntately it's not properly referenced. The previous version was absolutely terrible though, so I hope that this is at least an improvement on that. Regarding 'air' from what I gather this is correct - e.g. [1] [2]. Regarding 'dissolving' see this which as far as I know is one of the more up-to-date reviews. Judging by this I think you are right about the noise being ultrasonic. Feel free to be bold and improve the referencing etc. Cheers SmartSE (talk) 10:21, 13 October 2014 (UTC)

@Smartse:. Thanks for the links -- Not to pass the buck, but I'm woefully underqualified to go much further on this myself :-). It seems from the links in your reponse that xylem first undergoes "true" cavitation (as defined by this page, anyway), which can then lead to infiltration of air afterwards. In other words, the field of plant biology seems to have a colloquial usage of "cavitation" that is used to refer collectively to "true cavitation" and the potentially-following xylem embolism -- maybe this is the confusion that needs to be cleared up. The last article you linked to (re: audio) seems to explain all this rather well (page 2: "Cavitation results in a primarily vapor-filled conduit that eventually fills with air. A conduit in this air-filled state is embolized and is not available for water conduction."). That article also seem to confirm that the sounds happen in the audible frequency range and the inaudible range, but implies that they aren't loud enough to hear -- the source they give (#34) is here: [3] and describes the listening technique in a way that clearly implies that they are not audible without equipment. Chconnor (talk) 20:23, 13 October 2014 (UTC)

Circular definition

Cavitation is [..] the consequence of cavitational forces acting upon the cavitational liquid. Isn't cavitation really the formation of vacuum in microscopic places within a liquid, when a solid material, such as a propeller is moving faster than the liquid can follow?

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