Gas Turbine Handbook : Principles and Practices

Gas Turbine Systems Theory 49
COMPONENT EFFICIENCIES
The efficiency of each module contributes to the overall efficiency
of the gas turbine. The ability to examine the efficiency of each module
or component is a necessary tool in isolating engine problems.
Compressor Efficiency
Compressor efficiency (η c
) is directly proportional to the compressor
pressure ratio and inversely proportional to the compressor
discharge temperature. The following equation more exactly defines
compressor efficiency:
η c = R σ c –1
T o
–1
T i
(4-11)
where
σ = k –1
k
and
(4-12)
R c
= Compressor pressure ratio, P o
/P i
P o
= Compressor total discharge pressure, psia
P i
= Compressor total inlet pressure, psia
k = Ratio of specific heats, c p
/c v
c p
= Specific heat at constant pressure, Btu/lb °F
c v =
Specific heat at constant volume, Btu/lb °F
T o
= Compressor total discharge temperature, °R
T i
= Compressor total inlet temperature, °R
Compressor Horsepower (Required)
Compressor horsepower is the power that the compressor consumes
in compressing the air and moving it into the combustor.
HP c =
J
550 W ac p
T i
η c
P o
P i
σ
–1 =
J
550
W a c p (ÄT)
(4-13)
where W a
is the air flow entering the compressor in lb/sec.