文档介绍：Thermodynamics and Statistical Mechanics
Heat Engines and Refrigerators
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Thermo & Stat Mech - Spring 2004 Class 18
Carnot Cycle is Best
A Carnot cycle is the most efficient possible, operating between two reservoirs at temperatures T1 and T2.
Proof: Assume there is a more efficient engine. Let it produce work, and use that work to run a Carnot refrigerator between the same two reservoirs.
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Thermo & Stat Mech - Spring 2004 Class 18
Carnot Cycle is Best
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Thermo & Stat Mech - Spring 2004 Class 18
Carnot Cycle is Best
Then, Q1¢ < Q1. Also, W = Q1¢ – Q2¢ = Q1 – Q2.
So, Q1 – Q1¢ = Q2 – Q2¢, and Q2¢ < Q2 also.
Heat has been taken out of the low temperature reservoir and put into the high temperature reservoir with no expenditure of work!
Not possible.
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Thermo & Stat Mech - Spring 2004 Class 18
Otto Cycle (Gasoline Engine)
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Thermo & Stat Mech - Spring 2004 Class 18
Otto Cycle
W = Q1 – Q2
Q1 = CV(Tc – Tb)
Q2 = CV(Td – Ta)
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Thermo & Stat Mech - Spring 2004 Class 18
Otto Cycle
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Thermo & Stat Mech - Spring 2004 Class 18
Otto Cycle
and
Subtract, and get,
Then,
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Thermo & Stat Mech - Spring 2004 Class 18
Otto Cycle
is called pression ratio.
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Thermo & Stat Mech - Spring 2004 Class 18
Diesel Cycle
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Thermo & Stat Mech - Spring 2004 Class 18