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Smaller droplet creation by ultrasonic humidifiers

  1. Aug 7, 2013 #1
    Hi all,

    For a science project, I'm using mist, created by an ultrasonic humidifier.
    An ultrasonic humidifier uses a membrane that vibrates at ultrasonic frequency to disperse water into tiny droplets, resulting in a cool mist.

    Now I was wondering; is there a way to reduce the droplet size by adding something to the water? I really don't know much about chemistry but I would guess the droplet size depends on the viscosity or maybe the surface tension of the fluid?

    ps. The mist can be contained, and does not necessarily have to be used in an open room, so no health risks here.

    Tnx a lot!
  2. jcsd
  3. Aug 18, 2013 #2
    Hi Arnoke! I don't know very much about the physics affecting droplet size, but I agree that surface tension is likely an important variable. I would expect decreasing surface tension to reduce the droplet size. Surfactants (such as soap or detergents) decrease water's surface tension, so I would try adding some of these to the water. Keep me posted on if that works or not!
  4. Aug 21, 2013 #3
    Tnx for your response, ZacharyM.
    I'll definitely test it, once I get hold of a new vaporizer (broke my old one :)).
    The strange thing however, is that most manuals state that soap will indeed change the surface tension, stopping the vapor production as a result.
    e.g. http://amasci.com/amateur/clouds.html :
    "If you use soap to wash down the humidifier parts, rinse it very well afterwards. A small amount of soap in the water will change the surface tension and inhibit the mist production. If your device mysteriously stops making mist, try cleaning out the humidifier's water-pool section with non-soapy paper towels. As an experiment, drip some liquid soap into the operating humidifier to see what happens."
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