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Evaporation speed of liquids

  1. Mar 27, 2004 #1
    I'd like to know if there's any law/formula that allows you to calculate the evaporation speed of a liquid at a precise temperature, pressure, with a precise surface.
    Which physical parameters of the substance should i know?
    Thank You!

    Ciao!
    Andrea
     
  2. jcsd
  3. Mar 27, 2004 #2
    aursic,

    You need the rate of vaporization (in kg/m2) or some such units. You can probably find values tabulated in CRC or somewhere on the www. Try a google search.

    Being able to do much with the value you find is another story. Like you said, the rate depends on temp which can be determined pretty easily. But it also depends on the partial pressure of the vapor in question. Now just above the liquid/vapor surface, the two phases are very nearly in equilibrium so the vapor pressure is almost at the equilibrium value, meaning nearly no net transport of molecules across the surface would occur. This means the actual rate that evaporation occurs will usually have a huge dependence on tiny fluctuations in the actual partial pressure at the interface. These fluctuations can be caused by diffusion, convection, stirring etc. Sorting all that out in a real experiment gets pretty messy.

    Hope that helps and isn't too discouraging.
     
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