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Thread: Wet Nitrogen

  1. #1 Wet Nitrogen 
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    Jan 2021
    I have a nitrogen gas stream that is wetted using water at 50C in a bubbler tank , after that I need to calculate how much dry nitrogen gas has to be added to get a dew point of -20C.

    I have found that the vapor pressure of water at 50C is 123mbara. When the tank is at 1200mbara the fraction of water vapor should be 123/1200, is this correct ?

    How do I calculated the dew point of the wetted stream when I have only the fraction ?

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  3. #2  
    Bullshit Intolerant PhDemon's Avatar
    Join Date
    Feb 2013
    Newcastle-upon-Tyne, UK
    Ok I'm a bit rusty but I think what you need is as folliws:

    The 123/1200 s the relative humidity at 50 C (10.25 %)

    Next you need the saturation vapour pressure at -20 C. (0.1 kPa using Tetens formula)

    Calculate the relative humidity this vapour pressure would correspond to at 50 C. (0.1/12.36) = 0.81%
    [12.36 is the saturated vapour pressure of water at 50 C in kPa]
    This assumes the final mixture will also be at 50 C.

    Calculate the volumes of wet and dry nitrogen.
    Flow rate(wet) x 10.25 = 0.81 x Flow rate (wet + dry)

    So the ratio of wet and dry flow rates is 0.086.

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