# Calculating the relative humidity

1. Jul 23, 2014

### stackemup

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. Jul 25, 2014

### stackemup

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?

Thanks

3. Sep 15, 2014

### poortech

in my opinion both of your temperatures should be in °K, and P2 should be in absolute value, as your P1

4. Feb 16, 2017

### Jack Mc

These are my workings...

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

Formula:
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?

5. Feb 18, 2017

### Jack Mc

Was nearly right...