Compression

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Adiabatic compression

Compression power equation

When the compression is small, we can get away with the following simple equation:

1) W=(Q*dp)/n

Where:

W= compressor power (kW)

dp=pressure change (kPa)

Q=flow (m3/s)

n=compressor efficiency (usually between 0.6 and 0.8)

But when the compression becomes significant, we need to take into account the work done in compressing the gas.  The equation for adiabatic compression (no heat loss at the compressor) is still not exact, but it is OK for settlement design.

2)  W=(y/y-1)*[(Q*R*T)/(w*n)]*[(P2/P1)(y-1/y)-1]

Where:

W= power (Watts),

y= Heat capacity ratio[1] of the working fluid = 1.67 for noble gases = 1.41 for other gases, including air

Q= mass flow (kg/s)

R= Ideal gas constant = 8.314 J/kg mole

T= Absolute gas temperature before the compressor (K)

w= Molecular weight of the gas (g/mole)

n= Efficiency (from 0,null to 1, perfect)

P2= Absolute gas pressure after the compressor (kPa)

P1= Absolute gas pressure before the compressor(kPa)

Gas molecular weight
Hydrogen (H2) 2
Deuterium (D2) 4
Helium 4
Nitrogen (N2) 28
Air 28.9
Oxygen (O2) 32
CO2 44
Fluorine (F2) 38
Argon 40
Neon 20

Table 1, gas molecular weight, many gases are diatomic in their natural state