Lect No 08

1. Unit No:01
Thermodynamics
Prof. Yash B. Parikh
M.Tech (Computer Integrated Manufacturing)
B.E.(Mechanical Engineering)
Assistant Professor
Department of Mechanical Engineering

2. Entropy
2
 The term entropy was coined in 1865 by Rudolf
Clausius based on the Greek word
[entropía], meaning a turning toward.
 Entropy is an expression of disorder or randomness.
 Entropy is a thermodynamic property that can be
used to determine the energy not available
for work in a thermodynamic process.
 Entropy is denoted by letter S.
 Entropy is a function of quantity of heat and
temperature.
 The increase and decrease of entropy during a
process represents whether the heat is absorbed or
rejected by the system.

3. Entropy
3
 Ice melting in a warm room is a common example of
increasing entropy.
 If the system receives heat
from surroundings, the
entropy of the system
increases.
 Whereas entropy of
surroundings decreases.
 Entropy of an isolated
system remains constant.

4. Carnot Cycle
4
 The Carnot cycle is a theoretical thermodynamic
cycle proposed by Nicolas Léonard Sadi Carnot in the
year 1824.
 It is the most efficient cycle for converting a given
amount of thermal energy into work, or conversely,
creating a temperature difference (e.g. refrigeration)
by doing a given amount of work.
 Every thermodynamic system exists in a
particular thermodynamic state. When a system is
taken through a series of different states and finally
returned to its initial state, a thermodynamic cycle is
said to have occurred.
 In the process of going through this cycle, the
system may perform work on its surroundings,
thereby acting as a heat engine.

5. Carnot Cycle
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 A system undergoing a Carnot cycle is called a Carnot
heat engine, although such a 'perfect' engine is only
a theoretical limit and cannot be built in practice.

6. Carnot Cycle
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7. Carnot Cycle
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 The first process performed on the gas is
an isothermal expansion. The 300 degree heat
source is brought into contact with the cylinder, and
weight is removed, which lowers the pressure in the
gas. The temperature remains constant, but the
volume increases.
 During the process from State 1 to State 2 heat is
transferred from the source to the gas to maintain
the temperature. We will note the heat transfer
by Q1 into the gas.

8. Carnot Cycle
8
 The second process performed on the gas is
an adiabatic expansion. During an adiabatic
process no heat is transferred to the gas. Weight is
removed, which lowers the pressure in the gas. The
temperature decreases and the volume increases as
the gas expands to fill the volume. During the
process from State 2 to State 3 no heat is
transferred.

9. Carnot Cycle
9
 The third process performed on the gas is
an isothermal compression. The 200 degree heat
source is brought into contact with the cylinder, and
weight is added, which raises the pressure in the gas.
 The temperature remains constant, but the volume
decreases. During the process from State 3 to State
4 heat is transferred from the gas to heat source to
maintain the temperature.
 We will note the heat transfer by Q2 away from the
gas.

10. Carnot Cycle
10
 The fourth process performed on the gas is
an adiabatic compression. Weight is added, which
raises the pressure in the gas. The temperature
increases and the volume decreases as the gas
is compressed. During the process from State
4 to State 1 no heat is transferred.

11. Carnot Cycle
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 At the end of the fourth process, the state of the gas
has returned to its original state and the cycle can be
repeated as often as you wish.
 During the cycle, work W has been produced by the
gas, and the amount of work is equal to the area
enclosed by the process curves.
 From the first law of thermodynamics, the amount of
work produced is equal to the net heat transferred
during the process:
W = Q1 - Q2