Determining the absolute efficiency of any compressor requires a knowledge of a) the gas properties b) suction and discharge temperatures and pressures and c) gas flow.
a) and b) are usually quite easy to determine, but c) can be difficult, especially for a gas turbine compressor section.
What are you trying to achieve? If you are looking at compressor efficiency to determine wash intervals, then maybe a measure of EGT changes might be a better indicator.
Rolls Royce have a procedure involving trending non-dimensional intake dP against IP compressor speed for scheduling wash intervals.
Liebermanns book ‘Working Guide to Process Equipment’ suggests using the following formula ((P2/P1)-1)/(T2-T1) to give a trendable value of relative compressor efficiency
To determine the (isentropic) efficiency of a gas turbine compressor, such as the Frame 7 the airflow is not needed. The compressor efficiency can be calculated via:
Eff= (C-1)/(T2/T1-1)
Where C= Pr^((Gamma-1)/Gamma)
Eff is the isentropic efficiency, which is the same as adiabatic
Pr is the compressor pressure ratio
T2/T1 is the compressor temperature ratio
Gamma = cp/cv for air (approximately 1.4)
The RR method may not be suitable for a Frame7. The Frame7 has a VIGV/VSV and if active during normal operating power range (as we would find in a combined cycle plant) the RR method is not applicable.
EGT is Exhaust Gas Temperature and limits the engine from running too hot.
What are your temperature units - degrees F I think? Whatever units you use it should be in absolute (R or K). The efficiency should be bewteen 0.85(85%) to 0.9(90%). There is something wrong in your data. It gives 100% efficiency (assuming F for temperature)??? Where did you get these measurement?
Good books are GT Theory and GT Performance. We also sell GT simulators for training and education. If interested try
p1 = 14.7 (atmoshperic pressure)
p2 = 230 psi (compressor discharge pressure)
t1 = 75 deg F or 535 K (ambient temp)
t2 = 650 deg F or 1110 K (compressor discharge temp)
Gamma = cp/cv for air (approximately 1.4)
This is for a GE 7FA... I am taking these values right off the Mark VI during operation, am I missing something here? You are correct when I use these values the efficiency is to high... I am out of my specific area here so please bare with me.
I reviewed some internal data for the GE-F7A gas turbine and it appears that as gtsim suspected, your T2 temperature is too low. Your T2 should be on the order of 804 to 806 deg F at sea level 14.67 psia. The PR which you supplied is consistent with the data that I have for that particular gas turbine.
Therefore making using the higher compressor discharge temperature in the above calculations, your compressor efficiency should be approximately : 87%
