TEST_3_F95 - ME 326: THERMODYNAMICS I Test 3, Dec. 1, 1995...

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ME 326: THERMODYNAMICS I Test 3, Dec. 1, 1995 1) (33%) An inventor brings you a heat engine that she claims takes thermal energy from a solar collector at 227°C at a rate of 300 kW, converts 200 kW to mechanical power and rejects the rest to a cooling pond at 27°C. a) What is the thermal efficiency of this heat engine if it operates as claimed? b) Does this heat engine violate the first law of thermodynamics? c) Does this heat engine violate the second law of thermodynamics? (Provide some mathematical justification for your answers.) SOLUTION: a) h=W net /Q h =200/300=0.67 or 67% b) Write First Law around complete cycle: W net =Q h -Q c or Q c = Q h - W net =300-200 = 100 kW; As long as rejected rate of heat transfer is 100 kW, the device obeys the First Law . c) Can 1) Check whether efficiency of real device (0.67 from part a) is less than the ideal (Carnot) efficiency = 1 - (T c /T h ) =1-(27+273)/(227+273) =1 - (300/500) = 1 - 0.6 = 0.4. It’s not, so violates Second Law. or
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This note was uploaded on 02/07/2011 for the course ME 326 taught by Professor Schmidt during the Spring '07 term at University of Texas at Austin.

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TEST_3_F95 - ME 326: THERMODYNAMICS I Test 3, Dec. 1, 1995...

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