The second law of thermodynamics may be used to show that a cyclic heat power plant (or cyclic heat engine) achieves maximum efficiency by operating on a reversible cycle called the Carnot cycle for a given (maximum) temperature of supply (T-) and given (minimum) temperature of heat rejection (Tmin)
Such a Carnot power plant receives all its heat (QB) at the maximum temperature @.e. TB = Tmm) and rejects all its heat (QA) at the minimum temperature (i.e. TA = Tmin) the other processes are reversible and adiabatic and therefore isentropic. Its thermal efficiency is
Clearly raising T,, and lowering Thn will lead to higher Carnot efficiency.
The Carnot engine (or cyclic power plant) is a useful hypothetical device in the study of the thermodynamics of gas turbine cycles, for it provides a measure of the best performance that can be achieved under the given boundary conditions of temperature.
It has three features which give it maximum thermal efficiency:
(i) all processes involved are reversible;
(ii) all heat is supplied at the maximum (specified) temperature (T-);
(iii) all heat is rejected at the lowest (specified) temperature (Tmin).
In his search for high efficiency, the designer of a gas turbine power plant will attempt to emulate these features of the Carnot cycle.
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