relationships between turbines. Since the job of the high-pressure turbine is
to drive the compressor， the equations to use are:
h4α二h3 -Wca h4二h3 -(Wca/ηt) Thus， the output work can be represented by the relationship: Wα二(的內α +的內 )(h4α -h5)ηt (2-24) (2-25)(2-26)
ln the split-shaft cycle the first shaft supports the compressor and theturbine that drivesit， while the second shaft supports the free turbine that drives the load. The two shafts can operate at entirely different speeds. The advantage of the split-shaft gas turbine is its high torque at low speed. A free-power turbine gives a very high torque at low rpm. Very high torque at low rpm isconvenient for automotiveuse， but with constant full-poweroperation， it is of little or no value. lts use is usually limited to variable mechanical-drive applications.
The Regenerative Cycle
The regenerative cycle is becoming prominent in these days of tight fuel reserves and high fuel costs. The amount of fuel needed can be reduced by the use of a regenerator in which the hot turbine exhaust gas is used to preheat the air between the compressor and the combustion chamber. FromFigure 2-4 and the definition of a regenerator， the temperature at the exit of the regenerator is given by the following relationship:
T3二 T2α + ηreg(T5 -T2α)(2-27)
Where T2α is the actual temperature at the compressor exit. The regen-erator increases the temperature of the air entering theburner， thus reducing the fuel-to-air ratio and increasing the thermal efficiency.
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Figure 2-1.. The performance map of a regenerative gas turbine cycle.
For a regenerator assumed to have an effectiveness of80%， the efficiency of the regenerative cycle is about 40% higher than its counterpart in thesimplecycle， as seen in Figure 2-13. The work output per pound of air is about the same or slightly less than that experienced with the simple cycle. The point of maximum efficiency in the regenerative cycle occurs at a lowerpressure ratio than that of the simplecycle，but the opti內u內 pJessuJe Jαtio oJthe內αxi內u內 woJk is thesα內e in the two cycles. Thus， when companies aredesigning gas turbines， the choice of pressure ratio should be such that maximum benefit from both cycles canbe obtained， since most offer a regeneration option. lt is not correct to say that a regenerator at off-opti-mum would not be effective， but a proper analysis should be made before a large expense is incurred.
The split-shaft regenerative turbine is very similar to the split-shaft cycle.The advantage of this turbine is the same as that mentioned before;namely， high torque at low rpm. The cycle efficiencies are also about the same. Figure 2-14 indicates the performance that may be expected from such a cycle.
The Intercooled Simple Cycle
A simple cycle with intercooler can reduce total compressor work and improve net output work. Figure 2-7 shows the simple cycle with inter-cooling between compressors. The assumptions made in evaluating this cycle are: (1) compressor interstage temperature equals inlet temperature，
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本文鏈接地址：燃氣渦輪工程手冊 Gas Turbine Engineering Handbook 1(31)
