SECOND LAW OF THERMODYNAMICS
Thermodynamics
Carnot’s Principle
With the practice of using reversible processes, Sadi Carnot in 1824 advanced the study of the
second law by disclosing a principle consisting of the following propositions.
1.
No engine can be more efficient than a reversible engine operating between the
same high temperature and low temperature reservoirs. Here the term heat
reservoir is taken to mean either a heat source or a heat sink.
2.
The efficiencies of all reversible engines operating between the same constant
temperature reservoirs are the same.
3.
The efficiency of a reversible engine depends only upon the temperatures of the
heat source and heat receiver.
Carnot Cycle
The above principle is best demonstrated with a simple cycle (shown in Figure 21) and an
example of a proposed heat power cycle. The cycle consists of the following reversible
processes.
1-2:
adiabatic compression from TC to TH due to work performed on fluid.
2-3:
isothermal expansion as fluid expands when heat is added to the fluid at
temperature TH.
3-4:
adiabatic expansion as the fluid performs work during the expansion process and
temperature drops from TH to TC.
4-1:
isothermal compression as the fluid contracts when heat is removed from the fluid
at temperature TC.
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