Chapter 13 Gas Turbine Power Plants

where the numerator is proportional to the energy received by the
cooler air, and the denominator is the ideal heat transfer to the
cooler air. Values of s. depend on the effectiveness of the heat
exchanger design and the air flow rate, but typical values of effectiveness
lie in the range 0.6-0.8. Procedures for heat exchanger
design are presented by Incropera and DeWitt (1990).
Compressor and turbine work for the Brayton cycle with regeneration
are handled as with the basic cycle. Only the energy
addition in the combustor, as determined from (13.17), is different,
but this increases the thermal efficiency, since the denominator
of (13.1) is decreased while the numerator remains fixed. The
denominator Q A can be written alternatively as
M
(13.19)
where Mf IM a is the mass of fuel by the corresponding mass of
air, i.e., the fuel-air ratio F/A, introduced in Chapter 11. Since the
equivalent heat transfer Q A , resulting from the burning of fuel in
the combustor, is directly proportional to the mass of fuel burned
Mp and since Q A is reduced by the addition of the regenerator, the
amount of fuel required to produce a unit of net work is decreased,
i.e., the specific fuel consumption is reduced. Paralleling
the definition introduced in Chapter 11 for internal combustion
engines, specific fuel consumption (sfc) is defined by
m f
-f (13.20)
where mj denotes the mass flow rate of fuel and P represents the
net power produced by the gas turbine. Usually the power is the
shaft power to the load, as indicated in Figure 13.5, and the sfc is