lecture_8_03_02_2011

lecture_8_03_02_2011 - Heat Engines and Refrigerators Exam...

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Heat Engines and Refrigerators Exam II will be held on Friday May 6, 2011 Lecture 8 TIME: 7:00 – 9:00 PM PLACE: ARMS 3115
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Any device that has the primary purpose to convert heat to work is called a Heat Engine. DEFINITION First, a quick review of different types of heat engines
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Basic Idea gas h Mass = m A B C D Remove Heat! Apply Heat! V PdV mgh = i P B A D C Q in Q out Schematic:
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Simplified Steam Engine Piston Mechanical Linkage EXAMPLE I: Early heat engines were steam engines (Savery in 1698, Newcomen in 1705, Watt in 1770) Turning wheel Boiler Cold Condenser Steam
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High pressure Low pressure (Work comes from decrease of E int of steam) flywheel Modern steam engine An example of an external combustion engine Earliest steam engines were ~1% efficient (they burned enormous amounts of fuel!); by early 1900’s efficiencies reached ~10%; modern steam engines have efficiencies above 30%. Steam condenses to water at low pressure (invented ~1865) Clean water is recycled!
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Classic Heat Engines Rankine (steam) engine – 1859 (theory) Stirling engine - 1816 Internal Combustion (Otto) engine - 1876 1 st generation 2 nd generation Diesel engine - 1893
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Steam (Rankine) Cycle sentropic change water to steam Isentropic (constant entropy) expansion Isentropic compression change steam to water isentropic = quasistatic plus adiabatic E int = 0 Why?
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Example II: The Stirling Engine cooling fins o (Invented by Robert Sterling in 1816) http://en.wikipedia.org/wiki/Stirling_engine Heat Heat Heat Heat Characteristics: Recycles same trapped gas, quiet, low vibration, higher efficiency (~40%) than steam engine or internal combustion engine, low power applications. two pistons
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Moveable displacer w. shaft Moveable gas tight piston Loose- 1 2 3 4 5 (or 1) Flywheel not shown Cold Cold Cold Cold Cold Tube, open at top end, closed at bottom end fitting displacer (takes up space) Hot Hot P P P Hot P P gas
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lecture_8_03_02_2011 - Heat Engines and Refrigerators Exam...

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