The Carnot cycle consists of four reversible processes involving a working substance: (1) an isothermal expansion during which heat is absorbed from a hot reservoir, (2) an adiabatic expansion during which the temperature decreases, (3) an isothermal compression during which heat is rejected to a cold reservoir, and (4) an adiabatic compression during which the temperature increases, returning the system to the initial state. Nicolas Léonard Sadi Carnot published the first generalized theory of heat engines in 1824 based on this ideal Carnot cycle. The Carnot cycle establishes the maximum possible efficiency for a heat engine operating between two temperature reservoirs.

1. Carnot cycle
Presented by-
Rohan Ramesh Balkondekar
2019BME061 A56

2. History of Carnot cycle
• In the early 19th century, steam engines came to play
an increasingly important role in industry and
transportation.
• However, a systematic set of theories of the conversion
of thermal energy to motive power by steam engines
had not yet been developed.
• Nicolas Léonard Sadi Carnot (1796-1832), a French
military engineer, published Reflections on the Motive
Power of Fire in 1824.
• The book proposed a generalized theory of heat
engines, as well as an idealized model of a
thermodynamic system for a heat engine that is now
known as the Carnot cycle.
• Carnot developed the foundation of the second law of
thermodynamics and is often described as the "Father
of thermodynamics."

3. • Heat engine is a device
by which a system is
made to undergo a
cyclic process that
results in conversion of
heat into work.

4. Basic Heat Engine

5. MAIN PARTS OF HEAT ENGINE
1. HOT RESERVOIR
• SOURCE is a material kept at
high temperature and having
infinite thermal capacity. Any
amount of heat can be taken
from it without changing its
temperature.

6. 2. Sink
• COLD RESERVOIR or Sink is a
material kept at low temperature and
having infinite thermal capacity. Any
amount of heat can be given to it
without changing its temperature.

7. 3. Working Substance
• Working substance is a material which
converts heat energy in to work. It is
taken in a cylinder fitted with tight
movable frictionless piston. The lower
side of the cylinder will be thermally
conducting.

8. 4. Insulating Stand
• It insulates the working substance from
thermal contact with the surroundings.
That is used for performing the
adiabatic process.

9. Arrangement of all parts

10. Carnot Engine
• Carnot engine is an ideal heat engine
whose efficiency is maximum. In Carnot
engine, Carnot cycle is used. In carnot
engine, ideal gas is the working
substance, and all the dissipative forces
are absent.

11. Carnot Cycle
• Carnot devised an ideal cycle of
operation for a heat engine and is know
as Carnot cycle. In one complete cycle
of operation, there are four different
thermodynamic processes.

12. The Carnot
Cycle
The Carnot cycle consists of the following four processes:
1.A reversible isothermal gas expansion process.
2.A reversible adiabatic gas expansion process.
3.A reversible isothermal gas compression process.
4.A reversible adiabatic gas compression process.

14. PV Diagram of
the processes

15. Carnot cycle

16. TS diagram of processes

17. Isothermal Expansion
• At first, the working substance is kept in contact
with the source. The piston of the cylinder is
moved outwards. The gas expands at constant
temperature. The amount of heat (Q1 ) is
absorbed from the source to make the
temperature constant. The volume increases and
pressure decreases. This is called isothermal
expansion. It is represented by the curve 1-2 {AB}
in the indicator diagram.

18. Adiabatic Expansion
• The lower conducting side of the cylinder is kept in
contact with the insulating stand. The piston of the
cylinder is moved outwards. The gas expands
such that no heat enters the system or leaves
from it. The volume increases and pressure
decreases. The temperature is decreased from T1
to T2 . This is called adiabatic expansion. It is
represented by the curve 2-3 {BC} in the indicator
diagram.

19. Isothermal Compression
• The cylinder is kept in contact with the sink. The
piston of the cylinder is moved inwards. The gas is
compressed at constant temperature. The excess
heat produced(Q2 ) will flow to the sink to make
the temperature constant. The volume decreases
and pressure increases. This is called isothermal
compression. It is represented by the curve 3-4
{CD} in the indicator diagram.

20. Adiabatic Expansion
• The cylinder is kept in contact with the insulating
stand. The piston of the cylinder is moved
inwards. The gas is compressed such that no heat
enters the system or leaves from it. The volume
decreases and pressure increases. The
temperature increases from T2 to T1 . This is
called adiabatic expansion. It is represented by the
curve 4-1 {DA} in the indicator diagram.

21. Efficiency of Carnot engine
• We have the efficiency of heat engine, η = W/Q1 where
‘W’ is the work done and Q1 is the amount of heat
absorbed from the source.
• Also W = Q1 – Q2 where Q2 is the amount of energy
rejected to sink. There fore, η = ( Q1 – Q2 )/Q1 = 1 –
(Q2 /Q1 )
• For a carnot engine, it can be shown that η = 1 – (T2
/T1 ) where T1 is the temperature of source and T2 that
of sink.

22. Points to
remember
Carnot engine is purely an imaginary
engine. But all real engines are
constructed based on carnot cycle.
No other engine can have same efficiency
as that of a carnot engine working
between the same temperature range.