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Evaporation in 100% relative humidity

  1. Jun 23, 2012 #1
    hello guys

    if the water surface is at same temp as air above, and humidity is 100%, do any wataer molecules leave their liquid state to become vapour ie evaporate?

    I couldnt remember what professor said exactly, so i checked up on internet and it says

    water cant evaporate at 100% relatve humidity. But I vaguely remember it can..

    I am not so sure so can anyone clarify this please?

    What happen to net evaporation ie positive or zero. if the water surface is warmer than the air above at 100 humidity?

    thank you

    also, if the humidity is 50% at 20 degrees, what happen to evaporation rate as funtion of time? (two critical processes invovled)
     
  2. jcsd
  3. Jun 25, 2012 #2

    haruspex

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    Not all molecules in an ensemble will carry the same energy. Temperature only specifies the average. More energetic molecules in the water will evaporate, but at the same time the less energetic molecules in the air will condense. If the air is saturated at the water's temperature then these two processes will be in equilibrium.
    If the water is warmer then evaporation will exceed condensation, locally raising the temperature of the air. As the warmed air mixes with the cooler air around, some will recondense, forming a mist.
    As time passes, evaporation robs the water of its more energetic molecules, lowering the average energy (and hence temperature) of what remains.
     
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