Cavitation Thread

Serj

http://caltechbook.library.caltech.edu/1/02/bubbook.pdf

As you may or may not know cavitation is when the pressure of a liquid drops causing it to vaporize then the pressure returns and the vapor bubble implodes producing several interesting effects.

There are a few things I could not find in the document such as how they produced a single bubble and how to raise the temperature of the bubble at implosion.

FredGarvin

Great link Serj. I have never seen testing of this kind done in person. The only kinds I have seen involved boat props and pump impellers. It did not get down to the bubble level detail. I'll have to keep an eye out for more papers.

Serj

http://authors.library.caltech.edu/115/01/KUM113.pdf here's another one. I still can't figure out how to make a single bubble.

OnTheCuttingEdge2005

I believe the cavitation is caused when a focused Ultra Sound wave heats up the chemical by focused aggitation, The Focused Ultra Sound vibrates the chemical into a fusion velocity state at the focal point, the excessive cavitated heat generates bubbles, Like when you boil water and see bubbles but on a different principle and desired effect, The bubbles implode so fast they produce micro fusion states around the focal point.

They use a very high frequency Ultra Sonic Tranducer. The higher the better.

Gerald L. Blakley

Serj

I thought ultrasound was used for sonoluminescence? On the subject of sonoluminescence: why does a certain frequency cause a small bubble to expand and why does the bubble only expand to a certain limit then implode? And why does the bubble have to be so small?

OnTheCuttingEdge2005

Please read carefully on Sonic Fusion:
http://members.nuvox.net/~on.jwclymer/snf/


Gerald L. Blakley

Astronuc

Bubble size has to do with surface tension and pressure in a liquid. Small bubbles can coalesce into large bubbles. In boiling, bubbles nucleate as sites in a material (hence the name nucleate boiling), usually where the local temperature exceeds the saturation temperature for the liquid.

Nucleate boiling does occur in pressurized water reactors (PWRs), but it is limited, and bulk boiling, i.e. departure from nucleate boiling is expressely forbidden. Bulk boiling occurs (deliberately) in boiling water reactors, but dryout - where a sheath of steam forms on the fuel is expressly forbidden.

Ultrasound (acoustic energy) can be used to superheat a liquid to one can have bubbles of superheated vapor in a liquid which is subcooled. In addition to surface tension, the bubble pressure and heat conductance can limit size as well.

Serj

In a video of a bubble undergoing sonoluminescene, the buble ocillates momentarily after imploding. If the bubble was expanded again during its occilation (when the bubble is slightly bigger than normal size) would it expand more?

Pret

On going thru this thread, 'm reminded of these so called "cavitation generators" I read somewhr. these genrators use UHF sonic waves and can b used to blast a part of a mountain or dig de surface of the earth (instead of using dynamite).
the point tht intrigues me is, it's mentioned tht de focal point can be marked manually(by caliberations) and the sound waves can be directed at tht point from which vibrations start(more like the epicentre of an earthquake).

Is this kinda technology in use?

Serj

http://www.scs.uiuc.edu/suslick/imag...le.2cycles.mpg Why does the bubble behave like that? Why is there a 2 second pause were the bubble does nothing if the ultrasound is still on the entire time? How is bubble expansion related to the waves, does it grow as amplitude of the wave grows? Why does the bubble stop growing?

OnTheCuttingEdge2005

The Ultra sound frequency is pulsed.

If you are familure with how opera singers break crystal goblets with sound, First the opera singer gets the goblet to resinate then there is a slight pause then the opera singer hits a certain note that shocks the goblet into breaking.

I believe that once the bubble is in its resinate stage at full peak, The note is paused to a lower level then the high note shock pulse collapses the bubble just as the opera singer breaks goblets.

It pretty much has to do with the pulse duration and frequency and shock note, The pulse never gets fully turned off, Just lowered in modulation.

The first note sets up resinance and then it's lowered to allow the molecule to relax just a little while declining in resinance then a shock note is sounded which destablizes the shell structure causing it to rupture, The atmospheric pressure does the rest by implosion pressure.

There's probably more to it than that but I did my best to descibe it.

Gerald L. Blakley

ZeroGravity

Here is a link to a thesis on SingleBubbleSonoluminescence :
http://www.spetakelx.dk download the file : Sonoluminescence.pdf (7.8 MB)
And to answer a few questions.
The ultrasound field is keeping the bubble in place, so it doesn't drift up due to buoyancy.
The bubble is seeded (produced) in the almost air-free water by either plugging a needle through the surface, a short blow of air on the surface, passing an electrical current through a very small coil or by focusing a laser to vaporize some water. several bubbles are seeded this way and the "right" size bubbles are attracted to the center of the water filled container because of the ultrasonic field.

The bubble grows during the low pressure part of the ultrasound period, (see thesis front page blue line) as the sound pressure reach zero "overpressure" the bubble implodes under the pressure of the water (calculated by Lord Rayleigh (3rd), London, Edinburgh, and Dublin Philosophical Magazine
and Journal of Science (ser.6) 34, 94 (1917)).

The bubble heats up because of adiabatic compression, that is the air inside the bubble is compressed so fast that it cannot exchange heat with the water (temperatures of about 10000 K to maybe 100000 K) in this setup.

- All for now :)

OnTheCuttingEdge2005

I believe that by carefully choosing the liquid with the lowest vescosity would allow for a faster bubble collapse, It would be interesting if they chose Superfluid Liquid Helium as the liquid medium, Doing so may increase the efficiency of bubble collapse also, The zero vescosity of superfluid liquid Helium would collapse must faster than 3000 meters per second.

If anybody has contacts with anybody doing these experiments please try the SuperFluid Liquid Helium as the liquid medium.

Gerald L. Blakley

Serj

Thanks, that really helps! By "low prssure part of the ultrasound period" do you mean that the bubble growth happens over one half of a sound wave?

ZeroGravity

Yes just as the plot on the front page of the thesis shows.

In our experiment we used a frequenzy of about 25000 Hz,
so the bubble will expand and collapse 25000 times a second.
The frequenzy is chosen at one of the lowest resonances of the
spherical glass container which had a volume of 100 mL.

-The effect of the viscosity on the bubble collapse speed is small.
Simulations shows an increese from 1800 m/s to 2200 m/s upon changing
the liquid viscosity from that of water to zero.
It shortens the duration of the afterbounces so that at the end of the acoustic period, the bubble has stopped its oscillations. A 10 fold increase of viscosity will only decrease maximum bubble radius by 10% [S. Hilgenfeldt, M. Brenner, S. Grossmann and D. Lohse, J. Fluid. Mech. 365, p. 171 (1998)].
In water-glycerine mixtures used as host liquid the viscosity could be enhanced to a level where single bubble sonoluminescence (SBSL) is not possible, due to a damping of the collapse. This might be why Gaitan (the first guy to optain SBSL in 1990) was unable to get SBSL at water-glycerine mixtures above 60% glycerin(by weight)[S. Hilgenfeldt, M. Brenner, S. Grossmann and D. Lohse, J. Fluid. Mech.
365, p. 171 (1998)].
I am not sure if it has been done (SBSL in liquid helium).

Serj

According to the link the grows because of recitified diffussion so wouldnt the ammount of buble collapses will be significantly less than the number of waves?

Could SBSL be carried out without trapping the bubble in an acoustic if it was "trapped" instead by an extremely viscous gel? Or would SBSL not occur because of the viscosity?

Is measure of temperature an accurate measure of the heat in the bubble at implosion?

How do you increase Rmax?

Serj

would it be possible to increase Rmax by occilating the bubble on its first return (after it implodes)?