Ultrasonic cavitation

  1. Hi,

    I was wondering whether I could practically produce ultrasound capable of producing acoustic cavitation. I tried an arduino module at 40kHz, but this did bot work, would a higher frequency work? If so, is there a practical way of achieving this?

    Thanks in advance.
     
  2. jcsd
  3. Simon Bridge

    Simon Bridge 15,259
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    There is quite a lot of lit about acoustic cavitation - have you had a go getting hold of some?
    It looks like your frequency is high enough but your intensity probably isn't.

    A fairly typical setup would use 20kHz at 2kW.
    i.e. http://www.hielscher.com/cavitat.htm
     
  4. I was wondering of there was a way to apply the ultrasound without submerging in the liquid, i.e positioning transducers very close to the liquid surface. Would this be possible?
     
  5. You need good sound coupling to the water. When waves encounter a barrier where the material media changes properties there will be some reflection. It's doable but keep in mind that you'll lose some power from reflections off the water's surface.
     
  6. Bobbywhy

    Bobbywhy 1,908
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    In my estimation we cannot expect to induce cavitation by the application of the sound energy "very close to the liquid surface". As Okefenokee says, there is a BIG acoustic impeadance mis-match unlesss there is direct coupling. Hard to believe enough acoustic energy to cause cavitation could be forced across the transducer-air- liquid barrier. Why do sonograms require the "contact gel" to image a fetus?

    Cavitation in physics is the formation of vapor bubbles of a liquid in a region where the pressure of the liquid falls below its vapor pressure. The extreme pressure reduction literally “rips” the water molecules apart and creates a bubble. This bubble contains gas that had been dissolved in the liquid. Cavitation bubbles can easily be seen near the tips of a rapidly spinning propeller under water. For a good description of hydrodynamic cavitation, see: http://en.wikipedia.org/wiki/Cavitation

    Cavitation in liquids may also be caused when the low pressure portion of a powerful acoustic (sound) wave causes a bubble to form. When a cavitation bubble collapses it compresses the gas and vapor inside it to an extremely high temperature. This can be used to cause chemical reactions not possible without acoustic cavitation. Under some specific conditions the process will emit visible light called “sonoluminescence”.

    An excellent technical paper authored by some of the original pioneers in the field is this:
    “Acoustic cavitation and its chemical consequences”
    By Kenneth S. Suslick, et al.
    http://www.scs.illinois.edu/suslick/documents/philtrans99335.pdf

    See these images for acoustic cavitation:
    http://www.google.com/search?q=acou...QWiloCgAg&sqi=2&ved=0CD0QsAQ&biw=1333&bih=648

    Suggested search terms you may use in Google searches to learn more:

    hydrodynamic cavitation
    physics of acoustic cavitation in liquids
    acoustic cavitation ultrasound
    sonoluminescence

    Cheers, Bobbywhy
     
  7. Simon Bridge

    Simon Bridge 15,259
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    So your project had turned from something you needed to remove the bubbles from to something you want to add bubbles to?
     
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