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Author: mbeychok
Time: 01/07/06 13:53 PST
This is a reply to message no. 17208 by 737guy
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Current Topic:
energy required to compress air

For an ideal gas, the adiabatic head (H) required to compress a gas from P1 to P2 is:

H = [k/(k-1)] [R T1/9.806][(P2/P1)(k-1)/k - 1]

where:
H = adiabatic head, in meters
k = cp/cv = specific heat of gas at constant pressure/ specific heat at constant volume
T1 = inlet temperature, in °K (degrees Kelvin)
R = (universal gas constant, in J/kgmol•°K)/MW = 8314/MW
MW = molecular weight of gas (dimensionless)
P1 = absolute inlet pressure, in kPa (kiloPascals)
P2 = absolute discharge pressure. in kPa

The theoretical power (P) required is:

P = (F H)/1000 = [k/(k-1)] [w R T1/9806][(P2/P1)(k-1)/k - 1] 

where:
P = theoretical power, in kW (kilowatts) which is same as (Nm/s)/1000
F = (mass flow of gas, in kg/s)(9.806 m/s2), in kg•m/s3 which is same as N/s
N = Newtons
m = meters
s = seconds

To obtain the actual power, simply divide the theoretical power by the compressor efficiency which you will have to obtain from the manufacturer.

Please excuse my spelling the metric units ... this is done for those readers who (like myself) are struggling to get away from the USA customary units.

Milton Beychok
(Visit me at http://www.air-dispersion.com)

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