Handbook of Turbomachinery Second Edition Revised - Ventech!

The Mollier diagram is quite useful for diagnosing the influence of
moisture and impurities on various damage mechanisms. A first step in the
evaluation of blade damage may often be plotting the damage location on
the Mollier diagram to determine its relationship to the start of the phasetransition
zone.
Steam Cycles—Theory
A power plant cycle is the paths and processes through which a working
fluid passes, in a cyclic fashion, in the production of power by a prime mover
[7]. The efficiency of a power plant depends on the type of cycle,
temperatures and pressures in the cycle, the distribution of the working
fluid, and system losses. It is useful in the analysis of real systems to analyze
the so-called ideal cycles. Such analyses provide insights about the upper
bounds on efficiency, help characterize losses, and provide suggestions for
improvements in real-world equipment.
Here we examine three such cycles: the Carnot cycle; the simple or
base Rankine cycle; and the regenerative cycle.
Carnot Cycle
The Carnot cycle is illustrative because it represents the upper limit for
performance in a real system. The Carnot cycle is illustrated on a
temperature–entropy diagram in Fig. 9. It consists of two isothermal
processes and two isentropic processes. The Carnot cycle is completely
reversible, has no losses nor increases in entropy, and therefore represents
the ideal condition.
The Carnot efficiency is equal to
Where
Z Carnot ¼ 1
TA
TB
TA ¼ temperature of heat transfer into steam engine.
TB ¼ temperature of environment.
Efficiency will be the highest where the temperature of heat transfer
into the engine is at the highest possible temperature and the heat rejection is
at the lowest possible temperature. For example, for TA ¼ 1500 Fð1960 RÞ
and TB ¼ 60 Fð560 RÞ, the maximum thermal efficiency is approximately
73.5%. No real-world devices, which are all inherently irreversible, operate
at efficiencies as high as the ideal Carnot efficiency.
The expected efficiency of real-world energy conversion is also less by
Copyright © 2003 Marcel Dekker, Inc.
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