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Relative Humidity more than 100%

  1. Jul 26, 2011 #1
    In a calculation I am getting relative humidity more than 100%. What does it suggests?
    I know this means liquid water is also present in addition to saturated vapour. How should I calculate liquid water content then? Do I have to calculate activity first? Also what happens when I am considering diffusion of water vapour to a dry side (through a membrane)? Does liquid water present will evaporate to compensate drop in partial pressure of water vapour (considering total pressure remains constant)?
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  3. Jul 26, 2011 #2


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    It's raining.
  4. Jul 26, 2011 #3
    You haven’t said what your calculations were based on. If they were based on a simulation, it is entirely possible for the relative humidity to exceed 100%. If they were based on actual real world air conditions, then it is still possible, but very unlikely. Water droplets condense on foreign particles, such as dust, that are suspended in the air. Without such particles, condensation becomes difficult, and relative humidity’s as high as 800 % have been recorded in extremely clean air under laboratory conditions. In real life conditions, with all the combustion products and pollution that is present in the air, it is very unlikely that relative humidity will ever exceed 100%.
  5. Jul 26, 2011 #4
    I did calculations for a membrane humidifier. I am having dry air on one side and on other inlet I have humid air. The problem is that I am getting >100% RH in humid air. Partial pressure of water vapour is more than saturation pressure at that temperature
  6. Jul 27, 2011 #5
    Saturation vapor pressures are compiled for still air. If your air is in movement, it is entirely possible that your partial pressures should exceed the saturation pressure by a small amount. What is the magnitude of your excess vapor pressure? Is the RH being calculated or is it being measured? Keep in mind that all measurements are subject to measurement errors.
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