ME200 - Lecture 23

ME200 - Lecture 23 - 10/18/2010 MoreonThermodynamicCycles...

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10/18/2010 1 More on Thermodynamic Cycles Temperature scales ME 200 Thermodynamics I Purdue University , Dr. Tim Pourpoint – [email protected] Lecture 23 October 20 th , 2010 Up: Temperature distribution on the sun Right: Space Shuttle Main Engine with combustion temperature of ~3600 K Lecture Outline Last Lecture: More on the entropy statement of 2 nd law Heat Engines Refrigerators and heat pumps Perpetual motion machines Carnot cycle This Lecture: Carnot principle ME 200 2 Carnot principles Thermodynamic temperature scale Carnot heat engine Carnot refrigerator and heat pump
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10/18/2010 2 •2 nd law limits operation of cyclic devices as expressed by KP and Clausius statements –Hea t engine cannot operate by exchanging heat with a single reservoi Carnot Principles reservoir – Refrigerator cannot operate without net work input from external source •Ca rno t principles –The efficiency of an irreversible heat engine (or COP of an irreversible refrigerator/heat pump) is always less than the efficiency of a reversible one operating between the same two ME 200 3 reservoirs –The efficiencies of all reversible heat engines (or COP of all refrigerators/heat pumps) operating between the same two reservoirs are the same irrespective of the working fluid Carnot principles illustrated High Temperature Reservoir at T H 1 Irrev. HE 2 Rev. HE 3 HE ME 200 4 Low Temperature Reservoir at T L th,1 < th,2 th,2 = th,3
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10/18/2010 3 Proof of first Carnot principle High Temperature Reservoir at T H Q H Q H Rev. HE (or R) Irrev. HE Q L, irrev < Q L,rev Q L,rev W rev Combined HE + R Q L, irrev Q L,rev W irrev W irrev W rev ME 200 5 Low Temperature Reservoir at T L Low Temperature Reservoir at T L A reversible and an irreversible heat engine operating between the same two reservoirs (the reversible heat engine is then reversed to run as a refrigerator) The equivalent combined system Second Carnot principle illustrated High Temperature Reservoir at T H =1000 K A reversible HE, th,A Another reversible HE, th,B ME 200 6 Low Temperature Reservoir at T L =300 K th,A = th,B = 70%
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10/18/2010 4 • Independent of properties of substances used to measure temperature •Re ca l l 2 nd Carnot principle says all reversible heat engines Thermodynamic temperature scale (RHEs) have same efficiency operating between same two reservoirs •So efficiency of RHEs is independent of working fluid, it properties, details of cycle and engine •S in ce energy reservoirs are characterized by their
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This note was uploaded on 12/11/2011 for the course ME 200 taught by Professor Gal during the Fall '08 term at Purdue.

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ME200 - Lecture 23 - 10/18/2010 MoreonThermodynamicCycles...

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