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Calculating the relative humidity

  1. Jul 23, 2014 #1
    Can anyone help me with the below?

    Air is drawn into a compressor at normal temperature and pressure (N.T.P) and compressed to a pressure of 6 bar gauge. After compression the air is delivered at 1.2 m3 min-1 and cooled to a temperature of 30°C, at which point condensate is collected at the rate of 2 litres per hour. Estimate the FAD (N.T.P) of the compressor, and the relative humidity of the air entering the compressor.

    I have calculated the FAD to be 2.6324 m3 min-1 but I am unsure on the relative humidity?
  2. jcsd
  3. Jul 25, 2014 #2
    Hi, just to expand this is how I calculated the FAD

    V1= (P2 X V2 X T1) / (P1 X T2)
    V1= (6 X 1.2 X 15) / (30 X 1.013)
    V1= 108 / 30.39
    ∴ FAD of the compressor = 2.6324 m3 min-1

    For the relative humidity I believe the below formula is correct

    = absolute humidity / saturation quantity

    I believe the saturation quantity present is 12.5 g m-3.

    Can someone please advise me if I am correct so far and guide me how to find the absolute humidity?

  4. Sep 15, 2014 #3
    in my opinion both of your temperatures should be in °K, and P2 should be in absolute value, as your P1
  5. Feb 16, 2017 #4
    These are my workings...

    P1 = 1.013bar
    V1 = Unknown
    T1 = 15 + 273 = 288K
    P2 = 6 + 1.013 = 7.013
    V2 = 1.2 m³-1
    T2 = 30 + 273 = 303K

    V1= (P2 X V2 X T1) / (P1 X T2)
    V1= (7.013 X 1.2 X 288) / (303 X 1.013)
    V1= 2423.69 / 306.939

    ∴ FAD of the compressor = 7.89 m³ min-1

    Does this look correct?
  6. Feb 18, 2017 #5
    Was nearly right...
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