Previous in Forum: How to weld.032 stainless wire mesh . Next in Forum: Hardfacing of Valve Seat & Trim
Anonymous Poster

# Usefull Equations of Air compressor Systems

06/18/2008 1:10 AM

I would like to improve my knowledge on Air compressor Power out /input, air flow delicery versus pressure calculations.

welcome to any body willing to provide these equations

Interested in this topic? By joining CR4 you can "subscribe" to

Active Contributor

Join Date: May 2008
Posts: 17
#1

### Re: Usefull Equations of Air compressor Systems

06/18/2008 2:27 AM

hi

i can send U by mail 2 files.

Power-User

Join Date: Mar 2007
Location: Newburgh, IN
Posts: 285
#2

### Re: Usefull Equations of Air compressor Systems

06/18/2008 7:53 AM
__________________
Bud Trinkel
2
Commentator

Join Date: Aug 2005
Location: Greer, SC, USA
Posts: 73
#3

### Re: Usefull Equations of Air compressor Systems

06/19/2008 8:29 AM

From Machinery's handbook (which is a common reference for oil flooded compressor engineers), the HP to compress the air adiabatically is:

HP = [144*N*P*V*n] / [33000 (n-1)] * [(P2/P)^[(n-1)/(N*n)] - 1]

where N = number of stages in which compressions is accomplished

P = atmoshperic pressure in pounds per square inch

P2 = absolute terminal pressure in pounds per ssquare inch

V = volume of air , in cubic feet, compressed per minute, at atmospheric pressure (this is the rated cfm of the machine typically and relates to the intake cfm)

n=exponent of the compression curve = 1.41 for adiabatic compression

This is the HP required at the compressor to compress the air. Now you have factors including efficiencies of the bearing system in the compressor, the motor efficiency, and the drivetrain efficiency that will add to the power required by the motor. For a given compressor you can simplify the problem by measuring the power consumption of the compressor, calculating the theoretical horsepower, and then back-calculating the efficiency of the machine. However, you should note that this efficiency can change with speed, inlet air temperature, oil temperatures (for an oil cooled compressor), etc.

And then you can use the following formulas for calculating the relationship between pressure and volume in adiabatic compression of air:

P2/P1 = (V1/V2)^1.41

where P1 = initial absolute pressure in lbs/ft^2

P2 = absolute pressure in lbs/ft^2 after compression

V1 = initial volume in cubic feet

V2 = volume in cubic feet after compression.

Hope all this helps.

__________________
Self-motivational quote: "If they can make penicillin out of moldy bread, they can sure make something out of you." -- Muhammad Ali
Active Contributor

Join Date: Jun 2008
Posts: 16
#4

### Re: Usefull Equations of Air compressor Systems

06/19/2008 9:27 AM

Nate,

The majority of the oil flooded air compressors followed the polytropic process since some of the heat generated is removed. You happen to have the equations for those too?

Participant

Join Date: Jan 2010
Posts: 1
#5

### Re: Usefull Equations of Air compressor Systems

01/15/2010 5:05 AM

All this information I read in my thermal engineering book in my diploma....Thanks for sharing with us.

Interested in this topic? By joining CR4 you can "subscribe" to