Section summary |
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1. Formula |

2. Usual values |

For 1 compressor stage, the isentropic compression is the following

A compression is said isentropic when it is carried out by an ideal
compressor, without friction, without internal leakage and while
being perfectly insulated. To account for non idealities, the
calculation will have to be corrected by an efficiency coefficient
(η) dependent on the technology used.

P_{is}=Power (kW)

T_{suct}=Temperature inlet compressor (K)

T_{discharge}=Temperature outlet compressor (K)

M=Molar weight of gas (g/mol)

Qm=Compressor throughput (t/h) k=Gas isentropic coefficient

For air k=1.4

Reciprocating compressor high compression rate η=0.75

Reciprocating compressor low compression rate η=0.75

Rotary compressors η=0.7

Centrifugal compressors η is calculated from the polytropic
efficiency given by the manufacturer. A chart is then used to
calculate the polytropic coefficient of the gas, then the discharge
temperature calculated and then the actual power needed thanks to
the formula above.