Processing using cavitation

[Julian]

This video was flagged up either on here or the VOD a while back ... http://www.youtube.com/watch?v=Abw3dG0SB0g

They don't show a finished product, and I have my doubts they would get complete conversion in one pass.

I know ultrasonics are used in some commercial processes, which I believe creates cavitation, but suitable transducers are ferociously expensive.

There are many ways to mechanically create cavitation but has anybody had any thoughts on using cavitation to aid processing on an existing rig?

[Tony]

Well thanks to Mark I have a three phase gear pump, and I've got a VFD to drive it, just need to find the time to give it a whirl!

[photoman290]

looks interesting. wonder if a electric PSP would work.? cheap enough on fleabay to be worth a try.
 i have seen this system working and producing bio diesel when i was in cambridge. never got around to building one though. i still have all the bits around somewhere.

http://onlinelibrary.wiley.com/doi/10.1002/jctb.782/abstract;jsessionid=88770DF91FDABA07763ACFF0BA20CC3E.f01t04?deniedAccessCustomisedMessage=&userIsAuthenticated=false


As that was filmed in texas in may i suspect the ambient temperature was quite high.  someone will look it up. austin texas may 2009. i have a small gear pump i got for my centrifuge. still have to marry it to the motor. should work just as well for this.

[Julian]

OK, someone's got to ask ... PSP?

[Julian]

I was thinking of a modified centrifugal pump.

Many years ago I was involved in testing adding water to ships fuel by creating an emulsion.  The device doing the mixing was, for all intents and purposes, a modified pump, designed by one of the universities.

The impeller (although it claimed not to pump) was like an enclosed centrifugal jobbie, with serrations around it's circumference, running very close to the body (can't remember if the body was serrated, but it would make sense if it were).

The claim was that this created cavitation to emulsify the water/fuel mix.  Having done a little reading on cavitation, centrifugal pumps suffer cavitation if the cutwater is too close to the impeller, so the the theory would seem to be sound.

I've been toying with the idea of a winter project modifying a centrifugal pump, but if you chaps are that close to a pumped orifice system I may hold back to see the results.

[greasemonkey]

I think he is wrong..........

The mixture doesn't become bio because of the pressure drop, or cavitation.

The mix becomes bio, because of what the gears are doing to it in the gear pump. The pressure is a factor in this. I think he would get the same results if he took the cavitation piece, off altogether.

[nigelb]

I don't know whether this is relavent or not but my plant creates cavitation all the time when running....at the venturi. I know of another producer as well who is affected by this. Could this be an advantage in bio production?

Currently I eliminate it by opening the vent slightly to allow a bit of air to be drawn into into the venturi during ops.

[Julian]

I don't know whether this is relavent or not but my plant creates cavitation all the time when running....at the venturi. I know of another producer as well who is affected by this. Could this be an advantage in bio production?

Currently I eliminate it by opening the vent slightly to allow a bit of air to be drawn into into the venturi during ops.

Interesting ... how do you know cavitation is taking place?

[Julian]

I think he is wrong..........

The mixture doesn't become bio because of the pressure drop, or cavitation.

The mix becomes bio, because of what the gears are doing to it in the gear pump. The pressure is a factor in this. I think he would get the same results if he took the cavitation piece, off altogether.

A gear pump is actually quite gentle on a fluid ... in essence it takes a slug of liquid and pushes it through a cavity.  A centrifugal pump creates far more shear and turbulence.

Cavitation creates voids which collapse, firing a jet of liquid at very high speed and very high temperature, all be it for a couple of milliseconds, but it's this action which is claimed to create the conversion.

[photoman290]

psp power steering pump.

[greasemonkey]

A gear pump is actually quite gentle on a fluid ... in essence it takes a slug of liquid and pushes it through a cavity.  A centrifugal pump creates far more shear and turbulence.

Cavitation creates voids which collapse, firing a jet of liquid at very high speed and very high temperature, all be it for a couple of milliseconds, but it's this action which is claimed to create the conversion.

I see what you mean. I guess they must have done their homework anyway.
I agree that there must be a better way of inducing cavitation than just effectively spraying it at high (ish) pressure, if that is the essential bit of the equation.

[nigelb]

I don't know whether this is relavent or not but my plant creates cavitation all the time when running....at the venturi. I know of another producer as well who is affected by this. Could this be an advantage in bio production?

Currently I eliminate it by opening the vent slightly to allow a bit of air to be drawn into into the venturi during ops.

Interesting ... how do you know cavitation is taking place?

I think it was Tony that identified what was going on. The noise is incredable as the cavitation takes place at the out put side of the venturi. RichardP also has this phenomena.

I figured that I needed to eliminate it and the best way for me was by opening up the vent to the venturi ever so slightly. I suppose that prolonged exposure to it could cause issues in the venturi depending on where the void collapse takes place.

[greasemonkey]

I'm still not entirely sure i understand this. How can cavitation be induced under pressure, or by spraying?
Surely it needs something like a vacuum being created.
Wouldn't it be easier to induce cavitation by suction?

[Julian]

I'm still not entirely sure i understand this. How can cavitation be induced under pressure, or by spraying?
Surely it needs something like a vacuum being created.
Wouldn't it be easier to induce cavitation by suction?

It's not just pressure, it's a sudden change of pressure which creates, not a bubble, but a void.  The void is unsustainable and collapses with the effects described above.

This explains diagrammatically ...





An easy way to create cavitation is indeed on the suction of a pump.  If you throttle a valve on the suction, most pumps will cavitate, but it doesn't do the pump much good ...



Or on a boats propeller ...

[Julian]

I don't know whether this is relavent or not but my plant creates cavitation all the time when running....at the venturi. I know of another producer as well who is affected by this. Could this be an advantage in bio production?

Currently I eliminate it by opening the vent slightly to allow a bit of air to be drawn into into the venturi during ops.

If the video is to be believed, yes.

I can't remember your plant exactly, have you got a high capacity pump?  Is the venturi matched to the pump or is it under sized?  Possibly smoothing the throat may help, so there's not quite such a sharp change of profile.