8/11/2019 materi termo-Chapter7
1/37
The Second Law ofThermodynamics
Chapter 7
8/11/2019 materi termo-Chapter7
2/37
The first law of thermodynamics states that during any
cycle that a system undergoes, the cyclic integral of
the heat is equal to the cyclic integral of the work. However, we know from our experience that because
a proposed cycle does not violate the first lawdoes not
ensure that the cycle will actually occur.
It is this kind of experimental evidence that led to theformulation of the second law of thermodynamics.
8/11/2019 materi termo-Chapter7
3/37
In its broader significance the second law
acknowledges that processes proceed in a certain
direction but not in the opposite direction. A hot cup of coffeecools by virtue of heat transfer to
the surroundings, but heat will not flow from the cooler
surroundings to the hotter cup of coffee.
Gasolineis used as a car drives up a hill, but the fuellevel in the gasoline tank cannot be restored to its
original level when the car coasts down the hill.
8/11/2019 materi termo-Chapter7
4/37
7.1 HEAT ENGINES AND REFRIGERATORS
8/11/2019 materi termo-Chapter7
5/37
8/11/2019 materi termo-Chapter7
6/37
The first law of thermodynamics states that during any cyclethat a system undergoes, the cyclic integral of the heat is equalto the cyclic integral of the work.
8/11/2019 materi termo-Chapter7
7/37
8/11/2019 materi termo-Chapter7
8/37
8/11/2019 materi termo-Chapter7
9/37
8/11/2019 materi termo-Chapter7
10/37
8/11/2019 materi termo-Chapter7
11/37
8/11/2019 materi termo-Chapter7
12/37
7.2 THE SECOND LAW OF THERMODYNAMICS
Two classical statements of the second
law
KelvinPlanck statement
Clausius statement.
8/11/2019 materi termo-Chapter7
13/37
The KelvinPlanck statement:
It is impossible to construct a device that will operate in
a cycle and produce no effect other thanthe raising of
a weight and the exchange of heat with a singlereservoir.
See Fig. 7.6.
8/11/2019 materi termo-Chapter7
14/37
The Clausiu s s tatement:
It is impossible to construct a device that operates in a
cycle and produces no effect other than the transfer of
heat from a cooler body to a hotter body.See Fig. 7.7.
8/11/2019 materi termo-Chapter7
15/37
Equivalence of the two statements
(source)
(sink)
=0
8/11/2019 materi termo-Chapter7
16/37
(Impossible device)
8/11/2019 materi termo-Chapter7
17/37
7.3 THE REVERSIBLE PROCESS
A reversible process for a system
-- is defined as a process that once having taken place
can be reversed and in so doing leave no change ineither systemor surroundings.
8/11/2019 materi termo-Chapter7
18/37
8/11/2019 materi termo-Chapter7
19/37
8/11/2019 materi termo-Chapter7
20/37
7.4 FACTORS THAT RENDERPROCESSES IRREVERSIBLE
Friction
8/11/2019 materi termo-Chapter7
21/37
Unrestrained Expansion
8/11/2019 materi termo-Chapter7
22/37
Heat Transfer through a Finite Temperature
Difference
Mixing of Two Different Substances
8/11/2019 materi termo-Chapter7
23/37
Other Factors
hysteresis effects
i 2R loss encountered in electrical circuits
ordinary combustion
8/11/2019 materi termo-Chapter7
24/37
7.5 THE CARNOT CYCLE
8/11/2019 materi termo-Chapter7
25/37
8/11/2019 materi termo-Chapter7
26/37
8/11/2019 materi termo-Chapter7
27/37
7.6 TWO PROPOSITIONS REGARDING THEEFFICIENCY OF A CARNOT CYCLE
First Proposition
It is impossible to construct an engine that
operates between two given reservoirs and is moreefficient than a reversible engineoperating
between the same two reservoirs.
8/11/2019 materi termo-Chapter7
28/37
Second PropositionAll engines that operate on the Carnot cycle between two
given constant temperaturereservoirs have the same
efficiency.
8/11/2019 materi termo-Chapter7
29/37
The thermodynamic scale
8/11/2019 materi termo-Chapter7
30/37
8/11/2019 materi termo-Chapter7
31/37
7.7 THE IDEAL-GAS TEMPERATURE SCALE
Ttp.
8/11/2019 materi termo-Chapter7
32/37
How is the ideal-gas temperature determined ?
8/11/2019 materi termo-Chapter7
33/37
8/11/2019 materi termo-Chapter7
34/37
8/11/2019 materi termo-Chapter7
35/37
7.8 Ideal versus Real Machines
8/11/2019 materi termo-Chapter7
36/37
8/11/2019 materi termo-Chapter7
37/37
Top Related