Free air delivered and relative humidity.

Free air delivered and relative humidity.

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Axionknight

Original Poster:

8,505 posts

141 months

Wednesday 3rd February 2016
quotequote all
Folks of the science section, I'm looking for a bit of help/guidance with a question that has cropped up during my HND, the learning modules have left me scratching my head a bit to be honest, so any guidance or tips (happy to do the leg work myself of course as it's my education) would be gratefully received.

"Air is drawn into a compressor at N.T.P and compressed to a pressure of six bar gauge. After compression the air is delivered at "1.2m3 min-1" and cooled to a temperature of 30c at which point condensate is collected at the rate of two litres per hour. Estimate the free air delivered (N.T.P) of the compressor and the relative humidity of the air entering the compressor".

N.T.P = 15 degrees celcius and 1.013 bar/101.3kPA.




Free air delivered (V2)
Compressor inlet pressure (P1)
Volume at inlet (V1)
Pressure at compressor outlet (P2)

V2 = (P1 x V1)
-------
P2

or


V2 = (1.013 x 1.2)
-----------
6 = 0.02026 m3 min-1


So I think I've gotten that far (but perhaps it's all pish), just struggling with the relative humidity so any assistance is much appreciated beer

mike_knott

339 posts

230 months

Wednesday 3rd February 2016
quotequote all
It’s a while since I’ve done anything like this but if memory serves:

The compressor is delivering 1.2 m3/min of air at 6 barg (~7 bara). To approximate this flow rate at NTP you need to ratio the pressures, so the volume delivered would be:

1.2 * 7.013 / 1.013 = 8.3 m3/min.

Note that you can’t compensate for temperature as you don’t know the final temperature of the compressed gas (at 6 barg)].

For the relative humidity of the inlet air, you know there is [saturated content plus 2 kg/h] at 6 barg and 30 degC. You can calculate this as a mass of water in the 8.3 m3/min of air and then determine the relative humidity from tables.

What is the course, out of interest?

Mike…

Axionknight

Original Poster:

8,505 posts

141 months

Thursday 4th February 2016
quotequote all
HND in Instrumentation and Controls but several of the modules have a mechanical bias/crossover. It's done via distance learning so I'm just plodding through it in my own time. Tbh the rest of the module has been a piece of cake - I haveflown through it, just a wee head scratcher at this particular stage is all.


Cheers for the reply smile

mike_knott

339 posts

230 months

Thursday 4th February 2016
quotequote all
I&C is a good qualification to have at the moment; many chemical plants are trying to reduce manpower via increased automation so they are always looking for decent people.

Good luck.

Mike...

Axionknight

Original Poster:

8,505 posts

141 months

Thursday 4th February 2016
quotequote all
Cheers, I'm a sparky by trade, just branching out a bit as I work for a department in an oil field service company that does a lot of data acquisition work so it helps with that smile