Page 141 - DJJ20063- Thermodynamics 1
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DJJ20063- Thermodynamics 1
possible or impossible. We shall see, though, that a limit is imposed by the Second Law
of Thermodynamics, and that the possibility or otherwise of a process can be determined
through a property of the working fluid called entropy.
4.2 Analyze the concept of the second law of the thermodynamics.
4.2.1 Describe the property diagrams involving isentropic expansion and compression
process.
a) The Carnot cycle
From the Second Law of Thermodynamics it can be derived that no heat engine can be
more efficient than a reversible heat engine working between the same temperature
1
limits. Carnot, a French engineer, has shown in a paper written in 1824 that the most
efficient possible cycle is one in which all the heat supplied is supplied at one fixed
temperature, and all the heat rejected is rejected at a lower fixed temperature. The cycle
therefore consists of two isothermal processes joined by two adiabatic processes. Since
all processes are reversible, then the adiabatic processes in the cycle are also isentropic.
The cycle is most conveniently represented on a T-s diagram as shown in Fig. 4.2.1.
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