· Carnot Cycle
The Carnot cycle is the most efficient cycle possible. It consists of four basic reversible processes meaning that the cycle as a whole is also reversible. The four reversible processes are:
1. Isothermal expansion (by placing the system in contact with a heat reservoir with temperature T1).
2. Adiabatic expansion to T2 < T1.
3. Isothermal compression (by placing the system in contact with a heat reservoir with temperature T2).
4. Adiabatic compression from T2 to T1.
Carnot's Principle
An irreversible heat engine operating between two heat reservoirs at constant temperatures cannot have an efficiency greater than that of a reversible heat engine operating between the same two temperatures.
Another form of the Second Law of Thermodynamics or Carnot's Principle is that : It is not possible to make a heat engine whose only effect is to absorb heat from a high-temperature region and turn all that heat into work. That is, it is not possible to design a heat engine that does not exhaust heat to the environment. Or, it is not possible to design a heat engine that has an efficiency of 1.00 or 100%.
LIMITATIONS OF REVERSE CARNOT CYCLE
Isothermal process is possible if it is very slow and
isentropic process is possible if it very fast.
This alternate combination of very fast, very slow, very fast and very slow is not possible to achieve in actual practice and these are thus the limitations of this cycle.
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The isothermal and adiabatic processes take place during the same stroke. Therefoe the piston has to move very slowly for isothermal process and it has to move very faster during remaining stroke for adiabatic process which is practically not possible.
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