10.1SecondLawofThermodynamics - Second Law of...

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1 Second Law of Thermodynamics. 9.1 Second Law of Thermodynamics Carnot cycle efficiency -Heat engines - Refrigerators Second Law of Thermodynamics Heat engines (Kelvin-Planck Law) Refrigerators (Claussius Statement) Entropy Principle Three Statements of the second law Heat Engines A heat engine takes in heat at a high temperature and exhausts heat at a low temperature. In the process of heat flow some of the input heat is converted to work First Law (for a cycle) Q = Q h + Q c = W T c Second Law ( puts limits on Q h and Q C ) Kelvin-Planck Statement of the second law of thermodynamics Perfect heat engine It is impossible to construct a heat engine operating in a cycle that extracts heat from a reservoir and delivers an equal amount of work. No perfect heat engine Efficiency of a heat engine The efficiency is the fraction of the heat input at high temperature converted to work. hc hh QQ W e == In calculating efficiencies Q h and Q c are taken as positive quantities. (i.e. the magnitude of the heat) c h Q e1 Q =− The second law says that a heat engine cannot be 100% efficient. Carnot Cycle Sadi Carnot, a French engineer (1796-1832) proposed a cycle set the limits to the efficiency of a heat engine operating between two temperatures. The cycle consists of 4 reversible steps. 1. Isothermal expansion at T h 2. Adiabatic expansion from T h to T c 3. Isothermal compression at T c 4. Adiabatic compression from T c to T h. P V T h T c Q h Q c 1 2 3 4
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2 Heat engine. Heat engine undergoing the Carnot cycle.
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10.1SecondLawofThermodynamics - Second Law of...

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