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Unformatted text preview: ME320 Final Exam December 17, 2003 Name: Section: 1. Short questions (25 points) a. Does a heat engine that has a thermal efficiency of 100% neces- sarily violate: (i) the first law; (ii) the second law of thermody- namics? (Explain your answer.) It doesnt violate 1st law. But It violates the 2nd law, since no heat engine can have efficiency of 100%. b. A Carnot heat engine is operating between a source at T H and a sink at T L . In order to triple the initital thermal efficiency th of this engine, the initial performace th can be at most (a) th < 1; (b) th < 1 2 ; (c) th < 2 3 ; (d) th > 3 4 ; (e) th > 5 6 . (Circle your answer.) (c) c. A heat pump cycle absorbs heat from the environment at 5 C and supplies heat to a house at 22 C at a rate of 18,000 kJ/h. If the power consumed by the heat pump is 2.5 kW, the coefficient of performance of the heat pump is (a) 0.5 (b) 2.0 (c) 1.0 (d) 17.3 (e) 5.0. (Circle your answer.) (b) d. A power cycle operating between two reservoirs receives energy Q H by heat transfer from a hot reservoir at T H = 2000 K and rejects energy Q C by heat transfer to a cold reservoir at T C = 400 K. If Q H = 1200 kJ and Q C = 240 kJ, does the cycle operates reversibly or irreversibly? (Explain your answer.)reversibly or irreversibly?...
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This note was uploaded on 04/11/2008 for the course MASE 320 taught by Professor Shen during the Spring '08 term at Washington University in St. Louis.
- Spring '08