Gas Turbine Handbook : Principles and Practices

Gas Turbine Systems Theory 45
Chapter 4
Gas Turbine Systems Theory
GAS TURBINE OPERATING CYCLE
The gas turbine cycle is best depicted by the Brayton Cycle.
The characteristics of the operating cycle are shown on the
pressure-temperature map, the pressure-specific volume map,
and the temperature-entropy map (Figure 4-1a to 4-1c).
The gas turbine, as a continuous flow machine, is best described
by the first law of thermodynamics.
where
1 W 2
W ( 1
Q 2
) ≡ W (h 2
– h 1
+ KE 2
– KE 1
+ PE 2
– PE 1
+ ——)
J (4-1)
W* = Mass flow rate, lb m
/sec
1 Q 2
= H eat transferred to or from the system, Btu/lb m
h 2
= enthalpy of the fluid leaving, Btu/lb m
h 1
= enthalpy of the fluid entering, Btu/lb m
KE 2
= kinetic energy of the fluid leaving, Btu/lb m
KE 1
= kinetic energy of the fluid entering, Btu/lb m
PE 2
= potential energy of the fluid leaving, Btu/lb m
PE 1
= potential energy of the fluid entering, Btu/lb m
1 W 2 = Work per unit mass on or by the system, ft-lb f /lb m
J = Ratio of work unit to heat unit, 778.2 ft lb f
/Btu
1 W 2 /J = Work, Btu/lb m
*Here mass flow is designated by W to distinguish it from 1
W 2
, which is used
to designate work. Later in this text W a
and W f
(which are industry standards)
are used to designate air flow and fuel flow.
45