Second Law of
Thermodynamics
Prepared by ME B-2
PATEL PARIKSHIT SHAILESHBHAI130320102082
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• Heat engines
• Heat pumps and refrigerators
• Kelvin-Plank statement of
second law of thermodynamics
• Clausius statement of
second law of thermodynamics
• Equivalence of
Kelvin-Plank & Clausius statements
• Comparison between
Kelvin-Plank & Clausius statements
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Heat engines
 Heat engine receives
heat from high
temperature source (
furnace, nuclear reactor,
etc.
 It converts heat into
work.
 It rejects the remaining
waste heat to a low
temperature sink.
 It operates on complete
thermodynamics cycle.
Q1
Work = Q1-Q2
Q2
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Heat pumps and refrigerators
Q1 ( Desired output)
Wnet
Q2
Q1
Wnet
Q2 ( Desired output)
 Heat pumps absorbs heat from a low temp. body
and rejects it to a high temp. body.
 Refrigerators absorbs heat from low temp.
reservoir and supplying this heat to the high temp.
body.
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Kelvin-Plank statement of
2nd law of thermodynamics
“ It is impossible for any device as heat engine
that operates on a cycles to receive heat from a
single reservoir and produce a net amount of
work”.
“ No process is possible whose removes heat
from a single thermal reservoir at a uniform
temperature and performs equal amount of
work”.
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“ No het engine have
a thermal efficiency of
100%”.
“ To oprate power
plant, working fluid
must exchange heat
with the furnace as
well as the
atmosphere.”
Heat source at T1
Q1 = 100 kJ
W = 40 kJ
Q2 = 60 kJ
Heat sink at T2
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Clausius statement of
2nd law of thermodynamics
“ Heat can not itself flow from a colder body
to a hotter body.”
“ It is impossible to construct a device as heat
pump that operates in a cycle and produces no
effect other than the transfer of heat from a
lower temperature body to a higher
temperature body”
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“ No process is possible
whose removes heat
from a reservoir at lower
temperature and absorbs
equal amount of heat by
a reservoir at a higher
temperature without
any external assistant.”
Heat source at T1
Q1 = 100 kJ
W = 40 kJ
Q2 = 60 kJ
Heat sink at T2
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Equivalence
Violation of Kelvin-Plank statement leading to violation of
Clausius statement.
Q1 + Q2
Q1
Q2
W = Q1
Q2
Q2
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Equivalence
Violation of Clausius statement leading to violation of
Kelvin-Plank statement.
Q2
Q1
W = Q1-Q2
Q2
Q1-Q2
W = Q1-Q2
Q2
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