24 HANDBOOK OF ELECTRICAL ENGINEERING
Figure 2.5 Gas turbine thermodynamic cycle. Simple-cycle gas turbine.‘simple-cycle’ version of the Joule cycle. The main components of the gas turbine are shown in
Figure 2.5.
The thermodynamic relationships used to describe the operation of the gas turbine are the
pressure (P) versus volume (V) characteristic in Figure 2.6 and the temperature (T) versus entropy
(S) characteristic in Figure 2.7. These figures also show the effect of practical inefficiencies that
occur both in the air compressor and the turbine.
Air is drawn into the compressor at atmospheric pressureP 1 (in practice slightly lower due to
the inlet silencer, filter and ducting) and atmospheric temperatureT 1 , and compressed adiabatically
to a higher pressureP 2 to reduce its volume toV 2 and raise its temperature toT 2. The adiabatic
compression is given by the following equations; see standard textbooks e.g. References 1 to 5.
P 2 V 2
T 2=
P 1 V 1
T 1
=constant (2.1)P 2 V 2 γ=P 1 V 1 γ=constant (2.2)The work done in the compressor per kg of fluidUcis,
Uc=γ
γ− 1(P 2 V 2 −P 1 V 1 )( 2. 3 )
The following standard relationships apply,
P 1 V 1 =RT 1 (2.4)
P 2 V 2 =RT 2 (2.5)
Cp−Cv=R (2.6)
Cp
Cv=γ (2.7)