Gas Turbine compressor efficiency calculation
Gas Turbine compressor efficiency calculation
(OP)
Hello
I need to create a PI calculation that can trend compressor degradation. I have found an old calculation in xl from another plant that looks like this
A = RATIO OF PRESSURES AT INLET AND DISCHARGE =((BAROMETER + CDP) DIVIDED BY BAROMETER)RAISED TO THE EXP (0.28627)
B = RATIO OF TEMPERATURE AT INLET AND DISCHARGE = (INLET TEMP + 460) DIVIDED BY (COMP DISCHARGE TEMP+460)
FINAL EFFICIENCY CALC = (1- A)/(1-B)*100
What is EXP (.28627) and what is the 460 added to T1 and T2
Thank you for in advance
I need to create a PI calculation that can trend compressor degradation. I have found an old calculation in xl from another plant that looks like this
A = RATIO OF PRESSURES AT INLET AND DISCHARGE =((BAROMETER + CDP) DIVIDED BY BAROMETER)RAISED TO THE EXP (0.28627)
B = RATIO OF TEMPERATURE AT INLET AND DISCHARGE = (INLET TEMP + 460) DIVIDED BY (COMP DISCHARGE TEMP+460)
FINAL EFFICIENCY CALC = (1- A)/(1-B)*100
What is EXP (.28627) and what is the 460 added to T1 and T2
Thank you for in advance





RE: Gas Turbine compressor efficiency calculation
I don't have a clue what language you cut and pasted, but it is no programming language I'm familiar with. I'm going to assume it is program documentation and the phrase "RAISED TO THE EXP" means "^" so it would be:
[(P(bara)+P(disch))/P(bara)]^0.28627
If I misinterpreted and it is really "RAISED TO" exp(0.28627) why wouldn't they have just said "RAISED TO 1.331". In case you ditched algebra while you were avoiding physics "exp(x)" usually taken as e^x and "e" is called Euler's Constant and has a value of 2.71828.
So this is an air compressor and P(bara) is actually local atmospheric pressure and the term is generally called "compression ratios".
The part that makes no sense is that raising compression ratios >1 to .28627 is greater than 1. Ratio of temperatures is less than 1 so this equation results in "efficiency" around -150%. Negative efficiency is a bad thing. Efficiency greater than 100 is also pretty tough.
David
RE: Gas Turbine compressor efficiency calculation
"460" is the interest the bank charges per year in eurodollars per 1000 milliliters of displacement.
Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
RE: Gas Turbine compressor efficiency calculation
RE: Gas Turbine compressor efficiency calculation
FYI, this is a site where one engineering professional helps another and it is posted as such on the home page.
Not being an engineer, you should really engage the help of a mechanical engineer to answer your question, although the question already has been answered by zdas04, a registered ME.
Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
RE: Gas Turbine compressor efficiency calculation
((P2/P1)^0.28627-1) / ((T2-T1)/T1)
T1=inlet temp in Rankine
T2=discharge temp
P1=inlet presure in psia
P2=disharge pressure in psia
0.28672 = (k-1)/k, where k is the ratio of specific heats for air, which is somewhere around 1.4 depending on your average temperature.
RE: Gas Turbine compressor efficiency calculation
Thanks for describing the constant, I've been thinking about where it might have come from since the original post. So since:
T(adiabatic)=T1*(P2/P1)^((k-1)/k)
and your equation is
T1*[(P2/P1)^((k-1)/k)-1]/ΔT
That is the same as
(T(adiabatic)-T1)/(T2-T1)
It all makes sense as long as T2>T(adiabatic) which is generally true except when you have leaking suction valves (which cause the early introduction of gas and lower compression ratios and less heat of compression within the cylinder). This equation could easily show a malfunctioning machine as >100% efficient.
David