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MECH 213 - 10.3.07

# MECH 213 - 10.3.07 - Carnot Principles o Thermal efficiency...

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MECH 213 – October 3, 2007 Perpetual Motion Machines o PMM1 First law of thermodynamics o PMM2 Second Law of thermodynamics No such thing as a reversible process o Friction o Fluid mixtures Reversible output engine will always give maximal work output Reversible input engine will always give max work input o Use reversible engines as models o Internally reversible No irreversibilites inside system boundary o Externally reversible No irreversibilites outside the system boundary o Totally reversible No irreversibilites Carnot Cycle o State 1 State 2 ISOTHERMAL EXPANSION Isothermal heat input o State 2 State 3 ADIABATIC EXPANSION o State 3 State 4 ISOTHERMAL COMPRESSION Isothermal heat input o State 4 State 1 ADIABATIC COMPRESSION Reverse Carnot Cycle is a Carnot refrigeration cycle Anytime the direction of the cycle on the pv-diagram is counterclockwise, there is a required work input Carnot Engine is a perfect engine

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Unformatted text preview: Carnot Principles o Thermal efficiency of a reversible heat engine will be greater than the thermal efficiency of an irreversible one η th, rev > η th, irrev o The thermal efficiency of any thermal heat engine depends on the temperatures of the reservoirs Η th,rev = g(T H , T L ) • η th, A = 1 – Q 2 /Q 1 = f(T 1 ,T 2 ) η th, B = 1 – Q 3 /Q 2 = f(T 2 ,T 3 ) η th, C = 1 – Q3/Q 1 = f(T 1 ,T 3 ) η th, C = η th, A • η th, B T H = T 1 T L = T 3 Q 1 Q 1 A C Q 2 T 2 Q 3 B Q 1 p 2 A= Work output 4 3 v f(T 1 ,T 3 ) = f(T 1 ,T 2 )• f(T 2 ,T 3 ) φ(T 1 )/ φ(T 3 ) = [φ(T 1 )/ φ(T 2 )]•[ φ(T 2 )/ φ(T 3 )] Q1/Q2 = T1/T2 Q1/Q3 = T1/T3 Q2/Q3 = T2/T3 COP Ref = 1/[(Q H /Q L ) – 1] COP Ref, Carnot = 1/[(T H /T L ) – 1] COP HP = 1/[1 – (Q L /Q H )] COP HP, Carnot = 1/[1 – (T L /T H )] W net = (η th )(Q H )...
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MECH 213 - 10.3.07 - Carnot Principles o Thermal efficiency...

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