Thermodynamics and Statistical Mechanics

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Thermodynamics and Statistical Mechanics

• Heat Engines and Refrigerators

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Carnot Cycle
A Carnot cycle is an idealized reversible cycle
that operates between two heat reservoirs at
temperatures T1 and T2, where T2 gt T1. It can
operate as a heat engine, or a refrigerator.
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Carnot Cycle
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Carnot Cycle (Heat Engine)
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Carnot Cycle
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Carnot Cycle
For the entire cycle, Q W DU, and DU
0. The total heat equals the total work, Q
W. W Q2 Q1 Conservation of
energy. Q2 Q1 W
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Carnot Cycle
For an isothermal process
For an adiabatic process
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Path ab
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Paths bc, cd, and da
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Carnot Cycle
Divide ab by cd and then bc by da, and
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Thermal Efficiency (h)
If T1 0, h 1 (100)
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Refrigerator (Heat Pump)
Run the cycle in reverse. Do work W on the
system, remove Q1 from the low temperature
reservoir, and put Q2 into the high temperature
reservoir. As in a heat engine, Q2 Q1 W.
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Coefficient of Performance (for Refrigerator)
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Coefficient of Performance (for Heat Pump)
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Otto Cycle (Gasoline Engine)
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Otto Cycle

• W Q2 Q1
• Q2 CV(Tc Tb)
• Q1 CV(Td Ta)

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Otto Cycle
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Otto Cycle

• and
• Subtract, and get,
• Then,

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Otto Cycle

• is called the compression ratio.

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Diesel Cycle