capacity and temperature changes in compressor 1

[elham2590]

Hi,
I'm working on a two stage air compressor with capacity of 170 Nm3/hr, 9bar g.
It should be installed in a situation with Tmax=55 C and Tmin= 0 C and sea level=300m
In this situation how much temperature will change by being compressed? What is relation between T,P and V?
It's not an ideal gas and I think I cannot use PV=MRT
And does capacity change by changing temperature? By what relation?

 

[willard3]

PV=NRT works for air, but it's not terribly accurate. Probably good enough for what you're doing.

 

[elham2590]

and does sea level change anything in flowrate?

 

[MortenA]

If your knowledge of basic thermodynamics are so low (sorry for being blunt - im not trying to put you down just trying to get behind what you are writing) - then i would recommend that you seek assistance in-house or from a consultant. You can only get so much help at these pages - and how would you QA the work?

Best regards

Morten

 

[willard3]

+1 MortenA

Find an Engineer who knows thermodynamics/fluids....if you guess and you are wrong, there will be problems.

 

[chicopee]

Get a ME handbook and you'll find your answers.

 

[sheiko]

Good evening,

See the following thread:

http://www.eng-tips.com/viewthread.cfm?qid=285616&page=1

"We don't believe things because they are true, things are true because we believe them."

 

[Chemeng100]

Elham2590,

I suggest you start with performing an energy balance around the compressor (open system, no heat transfer to the system). Forget PV and T. I really wish I never learned it or ideal gases. Complete waste!!! Think in terms of entropy, enthalpy, internal energy, pressure and temperature.

You know the intlet pressure / temperature. Therefore, you know the state of the gas going INTO the compressor. You also know the pressure you are compressing to, right? Now you know the outlet pressure. Now you need to define another state variable on the outlet to figure out the new temperature. Hmm....???

Assume there is no heat transfered into or removed from the system. So Q = 0.

Also assume isentropic compression. That means that all the energy being transferred by the compressor is used to compress the gas. In other words, nothing is wasted. Now you have 2 state variables for the outlet of the compressor!! Pressure and entropy. Now you know pressure and entropy, you can find temperature.


We all know isentropic compression is not realistic. Why?? Because some energy from the gas is lost to the surrondings. But that will give you a theoretical temperature increase.

The real questions you should understand is why did the temperature increase? Not all gases increase in temperature when they are compressed? Hint: It has to do with the internal energy and the INTRA molecular forces.