Difference between revisions of "Compression"
(Created page with "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= compress...") |
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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. | 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)]*[(P<sub>2</sub>/P<sub>1</sub>)<sup>(y-1/y)</sup>-1] | |
Where: | Where: | ||
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W= power (Watts), | W= power (Watts), | ||
| − | y= Heat capacity ratio of the working fluid = 1.67 for noble gases = 1.41 for other gases, including air | + | y= Heat capacity ratio<ref>https://en.wikipedia.org/wiki/Heat_capacity_ratio</ref> of the working fluid = 1.67 for noble gases = 1.41 for other gases, including air |
Q= mass flow (kg/s) | Q= mass flow (kg/s) | ||
| Line 35: | Line 35: | ||
w= Molecular weight of the gas (g/mole) | w= Molecular weight of the gas (g/mole) | ||
| − | n= Efficiency | + | n= Efficiency (from 0,null to 1, perfect) |
P<sub>2</sub>= Absolute gas pressure after the compressor (kPa) | P<sub>2</sub>= Absolute gas pressure after the compressor (kPa) | ||
Revision as of 17:24, 17 April 2019
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
