Moisture content of compressed air

If at suction of compressor (1st stage) temp is 90F & RH 70% then air is compressed up to 22 psig what will be the temp & RH ?

If air at 90F & 70% RH at atm pressure is directly compressed to 100 psig what will be the temp, RH, dew point of this air?





Bill says...

Sounds like a school assignment to me, and I gave up doing homework a long, long time ago.

Sorry, I can't help you.

Cheers,

Bill

Comments for
Moisture content of compressed air

Click here to add your own comments

Jan 07, 2010
 About the calculations
by: Sorlozer

Hey. Nice to see someone interested in the details of compression stage.

Well I can give you some background, since I don't know the exact values of the resulting compression stage.

First, we must know that Compressors are normally Isentropic Process, or Reversible Adiabatic Process (refer to the internet of you want to know the details). Meaning, Compression is not just a Volume-Pressure Relationship, wherein Volume is directly inversely proportional to each other. Temperature, and Enthalpy changes as well. Only the Entropy does not change. That is theoretical.

However, in real-life situation, Compression is irreversible. Meaning, if you want to reverse the process, additional input is required just to return the condition of air to its previous state (refer to Law of Thermodynamics). Be compression, we know that the Pressure increases as Volume decreases, at the same time, the temperature increases, depending on the status of the compressor.

If the compressor is running very frequently, then you might want to expect the temperature of the Compressor to be 80-110C, meaning that the temperature of air during the compression stage has a lot of kicking molecules as pressure builds up, which results to higher disorder, lower Compression Efficiency, and higher energy loss.

Relative Humidity after compression is assumed to remain the same.

However, based on the Psychometric Chart, if temperature decreases, condensate formation is inevitable. And as air goes to the receiver, the temperature of air will go down to match with the atmospheric temperature.

That is when the condensate occur.

So, if the inlet air temperature and RH are 90F and 70% respectively, then we must learn that for every 4C rise in inlet air temperature, there will be 1% higher energy consumption.

Also, the immediate outlet temperature after compression should be higher as explained above, and the Relative Humidity has a high chance of remaining the same, although we won't be able to determine the exact value due to the compression stage existing inside the system, and the quality of air can't be determined of the air inside compression is isolated.

Normally, RH should have a value of 36%. 70% RH is too high, and signals us that the conditions of air in that area is not good.

One suggestion might be to isolate the compressor and put it on a air-conditioned system, and set its temperature to around 20C, and its RH to 0%, if applicable.

I hope the information I gave will bring more people to learn more about their ACS.

Thanks.
_________________

Most welcome. Thank you. Wish I understood more of what you wrote. :-)

Cheers,

Bill

Click here to add your own comments

Join in and write your own page! It's easy to do. How?
Simply click here to return to Miscellaneous Compressor Issues