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Thermo & Stat Mech - Spring 2006 Class 5 1 Thermodynamics and Statistical Mechanics Heat Engines and Refrigerators

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Thermo & Stat Mech - Spring 2006 Class 52 Carnot Cycle A Carnot cycle is an idealized reversible cycle that operates between two heat reservoirs at temperatures T 1 and T 2, where T 2 > T 1. It can operate as a heat engine, or a refrigerator.

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Thermo & Stat Mech - Spring 2006 Class 53 Carnot Cycle

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Thermo & Stat Mech - Spring 2006 Class 54 Carnot Cycle (Heat Engine)

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Thermo & Stat Mech - Spring 2006 Class 55 Carnot Cycle

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Thermo & Stat Mech - Spring 2006 Class 56 Carnot Cycle For the entire cycle, Q = W + U, and U = 0. The total heat equals the total work, Q = W. |W| = |Q 2 | – |Q 1 | Conservation of energy. |Q 2 | = |Q 1 | + |W|

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Thermo & Stat Mech - Spring 2006 Class 57 Carnot Cycle For an isothermal process: For an adiabatic process:

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Thermo & Stat Mech - Spring 2006 Class 58 Path a b

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Thermo & Stat Mech - Spring 2006 Class 59 Paths b c, c d, and d a

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Thermo & Stat Mech - Spring 2006 Class 510 Carnot Cycle Divide a b by c d and then b c by d a, and

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Thermo & Stat Mech - Spring 2006 Class 511 Thermal Efficiency ( ) If T 1 = 0, = 1 (100%)

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Thermo & Stat Mech - Spring 2006 Class 512 Refrigerator (Heat Pump) Run the cycle in reverse. Do work |W| on the system, remove |Q 1 | from the low temperature reservoir, and put |Q 2 | into the high temperature reservoir. As in a heat engine, |Q 2 | = |Q 1 | + |W|.

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Thermo & Stat Mech - Spring 2006 Class 513 Coefficient of Performance (for Refrigerator)

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Thermo & Stat Mech - Spring 2006 Class 514 Coefficient of Performance (for Heat Pump)

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Thermo & Stat Mech - Spring 2006 Class 515 Otto Cycle (Gasoline Engine)

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Thermo & Stat Mech - Spring 2006 Class 516 Otto Cycle W = |Q 2 | – |Q 1 | |Q 2 | = C V (T c – T b ) |Q 1 | = C V (T d – T a )

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Thermo & Stat Mech - Spring 2006 Class 517 Otto Cycle

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Thermo & Stat Mech - Spring 2006 Class 518 Otto Cycle and Subtract, and get, Then,

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Thermo & Stat Mech - Spring 2006 Class 519 Otto Cycle is called the compression ratio.

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Thermo & Stat Mech - Spring 2006 Class 520 Diesel Cycle

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