The Naked Scientists

The Naked Scientists Forum

Author Topic: Breaking the sound barrier in a liquid  (Read 3768 times)

Offline j_hendrixpurplehaze

  • First timers
  • *
  • Posts: 2
    • View Profile
Breaking the sound barrier in a liquid
« on: 04/05/2006 22:34:58 »
What happens when the sound barrier is broken in a liquid?

I recently read an article on Sonoluminescence which seems to show what happens to air bubbles as sound waves cause them to collapse inward (implode.) If this is the case would it also be true that light would be created by imploding the vortex created by exceeding the speed of sound in a liquid?

Anyone have any thoughts?



 

Offline neilep

  • Withdrawnmist
  • Naked Science Forum GOD!
  • *******
  • Posts: 20602
  • Thanked: 8 times
    • View Profile
Re: Breaking the sound barrier in a liquid
« Reply #1 on: 04/05/2006 22:46:33 »
Great post J (can i call you 'J ' ?... as I am too tired to write hendrixpurplehaze  .....DOH !!)

I haven't got a clue myself, but I recently asked a sound barrier orientated question and so hopefully the clever bods who helped me out will also help you out too..

....oh....and welcome to the site !

Men are the same as women, just inside out !
 

another_someone

  • Guest
Re: Breaking the sound barrier in a liquid
« Reply #2 on: 05/05/2006 00:10:09 »
Looking at the wikipedia pages on sonoluminescence and cavitation (http://en.wikipedia.org/wiki/Sonoluminescence and http://en.wikipedia.org/wiki/Cavitation):

Sonoluminescence is a consequence of cavitation, and the very rapid implosion of the cavities.  Cavitation can occur even at subsonic speeds, but much as the cavities can implode (and can generate enough heat to cause serious damage to propellers and other machinery), the question is how rapidly they implode.

In cavitation that creates sonoluminescence (i.e. that created by ultrasonic transducers), the temperature inside the cavity can reach 20,000 kelvin.

http://en.wikipedia.org/wiki/Sonoluminescence
quote:

Sonoluminescence may or may not occur whenever a sound wave of sufficient intensity induces a gaseous cavity within a liquid to quickly collapse. This cavity may take the form of a pre-existing bubble, or may be generated through a process known as cavitation. Sonoluminescence in the laboratory can be made to be stable, so that a single bubble will expand and collapse over and over again in a periodic fashion, emitting a burst of light each time it collapses. For this to occur, a standing acoustic wave is set up within a liquid, and the bubble will sit at a pressure anti-node of the standing wave. The frequencies of resonance depend on the shape and size of the container in which the bubble is contained.

Some facts about sonoluminescence:

  • The light flashes from the bubbles are extremely short—between 35 and a few hundred picoseconds long.

  • The bubbles are very small when they emit the light—about 1 micrometre in diameter.

  • Single-bubble sonoluminescence pulses can have very stable periods and positions. In fact, the frequency of light flashes can be more stable than the rated frequency stability of the oscillator making the sound waves driving them.

  • For unknown reasons, the addition of a small amount of noble gas (such as helium, argon, or xenon) to the gas in the bubble increases the intensity of the emitted light dramatically.


The wavelength of emitted light is very short; the spectrum can reach into the ultraviolet. Light of shorter wavelengths has higher energy, and the measured spectrum of emitted light seems to indicate a temperature in the bubble of at least 20,000 kelvins, up to a possible temperature in excess of one megakelvin. Some estimates put the inside of the bubble at one gigakelvin [1]. These estimates are based on models which cannot be verified at present, and may include too many unsupported assumptions.

Temperatures this high make the study of sonoluminescence especially interesting for the possibility that it might produce a method for achieving thermonuclear fusion. If the bubble is hot enough, and the pressure in it is high enough, fusion reactions like those that occur in the Sun could be produced within these tiny bubbles. This possibility is sometimes referred to as bubble fusion. Recent experiments (2002, 2005) of R. P. Taleyarkhan, et.al., using deuterated acetone, show measurements of tritium and neutron output consistent with fusion, but these measurements have not been reproduced outside of the Taleyarkhan lab and remain controversial. Brian Naranjo of the University of California, Los Angeles, has recently completed an analysis of the Taleyarkhan results claiming that Taleyarkhan had most likely misinterpreted the radioactive decay of standard lab materials for the byproducts of nuclear fusion. Taleyarkhan's patent application has also been rejected.

Writing in Nature, chemists David J. Flannigan and Kenneth S. Suslick study argon bubbles in sulfuric acid and show that ionized oxygen O2+, sulfur monoxide, and atomic argon populating high-energy excited states are present implying that the bubble has a hot plasma core. They point out that the ionization and excitation energy of dioxygenyl cation is 18 electronvolts, and thus cannot be formed thermally; they suggested it was produced by high-energy electron impact from the hot opaque plasma at the center of the bubble (Nature 434, 52 - 55 (03 March 2005); doi:10.1038/nature03361).

On January 27, 2006, researchers at Rensselaer Polytechnic Institute claimed to have produced fusion reactions by sonoluminescence, without an external neutron source, according to a paper published in Physical Review Letters. To date, these results have not been reproduced by other members of the scientific community.



Given the very short time-scales in which the implosion is supposed to happen, and it only happens at ultrasonic frequencies, not ordinary sound frequencies, would lead me to be sceptical about whether they could be created my simple hydrodynamic effects.

The speed of sound in water is between 1450 and 1500 m/s (upwards of around 3260 mph).  I don't know if this could cause the kind of abrupt implosion of cavities that would cause sonoluminescence, but it is quite a high speed to attempt to achieve to try and prove the point.



George
« Last Edit: 05/05/2006 03:03:54 by another_someone »
 

another_someone

  • Guest
Re: Breaking the sound barrier in a liquid
« Reply #3 on: 05/05/2006 02:58:08 »
OK, thinking about this a bit more (and maybe someone will come along and show me the flaw in my logic), I would suggest that sonoluminescence is not possible in supersonic travel through water.

The simplest reason is that since supersonic travel through water would require travel in excess of 3260 mph, the frictional forces would be sufficient to boil the water, and the hot steam will not implode.  It is possible that other physical processes may be initiated by the intense frictional processes that may be in some way luminescent, but it would not be through cavitation, and so would not be the same process as causes sonoluminescence.

Ofcourse, since water (or any liquid) is largely incompressible (unlike a gas), shock waves can be formed at very much lower speeds (in fact, I think the bow wave of a ship would be regarded as a low energy shock wave).  It is also true that cavitation can occur at subsonic speeds (and can become a serious problem in badly designed propellers since in increases noise, reduces efficiency, and can damage the propeller.

But there is another difference between cavitation that creates sonoluminescence and most other forms of cavitation, and that is the size of the bubbles created.  The important thing about  sonoluminescence is not the amount of energy contained in the cavity, but the high density of the energy, because the cavity is small and collapses very fast.  This all happens because the cavity is created within one wavelength of an ultrasonic sound wave.



George
 

Offline j_hendrixpurplehaze

  • First timers
  • *
  • Posts: 2
    • View Profile
Re: Breaking the sound barrier in a liquid
« Reply #4 on: 05/05/2006 14:59:20 »
Quote
Originally posted by j_hendrixpurplehaze

What happens when the sound barrier is broken in a liquid?

Thanks guys for the replies. (You can call me whatever you like.):)

The info on cavitation was cool. The wikipedia info on supercavitation was interesting. By the way wikipedia is a great place for obtaining science info. I will refer to Sonoluminescence from now on as SL for ease.

I was thinking more about this on my drive home yesterday, and here are somemore rabbit trails I came to.

Let us for the sake of argument rule out SL as a possible outcome of breaking a liquid sound barrier. My question still holds what then is the result? It certainly is a large speed just to prove a point but isn't that what physics is all about?

If you will allow me to digress for a moment to make an analogy by way of a fun quote: "Nothing so absurd can be said that it has not been said by some philosopher."
 --Cicero

I would say (with a big smirk ;)) that the same could be said of experiments proposed by physicists. As to directly related to liquid supersonic speeds this would not have to be an object of significant mass, although that would be more entertaining. Even a small projectile of some sort would be interesting.

Here is another possibility although possibly less related. Cherenkov radiation happens when an electron travels faster than the speed of light its respective medium. The “blue glow” is eerily similar to that of SL. If we consider de Broglie wave type implications with relation to mass and speed but then have some way to relate it to the index of refraction in the meduim via n = c/v with some formula would we come up some sort of visible wave emission?  

I wonder...
 

 

The Naked Scientists Forum

Re: Breaking the sound barrier in a liquid
« Reply #4 on: 05/05/2006 14:59:20 »

 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums