Transcript ch07 second law.ppt

Chapter 7
THE SECOND LAW OF THERMODYNAMICS
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07-03
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07-02
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07-07
The Kelvin-Planck Statement of the
2nd Law of Thermodynamics
It is impossible to construct a device that
will operate in a cycle and produce no
effect other than the raising of a weight
and the exchange of heat with a single
reservoir.
07-03
07-04
07-08
The Clausius Statement of the
2nd Law of Thermodynamics
It is impossible to construct a device that
operates in a cycle and produce no effect
other than the transfer of heat from a
cooler body to a hotter body.
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07-09
The Reversible Process
A process that, once having taken place,
can be reversed and in so doing leave no
change in either system or surroundings.
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07-13
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Heat Transfer Through a Finite
Temperature Difference
We know from experience that heat energy flows
naturally from a high-temperature reservoir to a lowtemperature reservoir. To reverse that process we
would need to provide a heat pump (refrigerator), which
requires work from the surroundings and heat transfer
to the surroundings.
07-16
The Carnot Cycle
• A reversible isothermal process in which heat is
transferred to, or from, a high-temperature reservoir.
• A reversible adiabatic process (no heat transfer) in which
the temperature of the working fluid decreases from the
high temperature to the low temperature.
• A reversible isothermal process in which heat is
transferred to, or from, the low-temperature reservoir.
• A reversible adiabatic process in which the temperature
of the working fluid increases from the low temperature
to the high temperature.
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Two Propositions
• It is impossible to construct an engine that operates
between two given reservoirs and is more efficient
than a reversible engine operating between the same
two reservoirs.
• All engines that operate on the Carnot cycle between
two given constant-temperature reservoirs have the
same efficiency.
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07-24
Ideal vs Real Machines
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07-un01
07-un02
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p07-101
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