Chapter_10 - Chapter 10 10-8C Heat rejected decreases;...

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Unformatted text preview: Chapter 10 10-8C Heat rejected decreases; everything else increases. 10-12C The boiler exit pressure will be (a) lower than the boiler inlet pressure in actual cycles, and (b) the same as the boiler inlet pressure in ideal cycles. 10-16 A simple ideal Rankine cycle with water as the working fluid operates between the specified pressure limits. The maximum thermal efficiency of the cycle for a given quality at the turbine exit is to be determined. Assumptions 1 Steady operating conditions exist. 2 Kinetic and potential energy changes are negligible. Analysis For maximum thermal efficiency, the quality at state 4 would be at its minimum of 85% (most closely approaches the Carnot cycle), and the properties at state 4 would be (Table A-5) K kJ/kg 7440 . 6 ) 8234 . 6 )( 85 . ( 9441 . kJ/kg 3 . 2274 ) 3 . 2335 )( 85 . ( 27 . 289 85 . kPa 30 4 4 4 4 4 4 fg f fg f s x s s h x h h x P Since the expansion in the turbine is isentropic, kJ/kg 5 . 3115 K kJ/kg 7440 . 6 kPa 3000 3 4 3 3 h s s P Other properties are obtained as follows (Tables A-4, A-5, and A-6), kJ/kg 31 . 292 04 . 3 27 . 289 kJ/kg 04 . 3 m kPa 1 kJ 1 kPa ) 30 3000 )( /kg m 001022 . ( ) ( /kg m 001022 . kJ/kg 27 . 289 in p, 1 2 3 3 1 2 1 in p, 3 kPa 30 @ 1 kPa 30 @ 1 w h h P P w h h f f v v v Thus, kJ/kg . 1985 27 . 289 3 . 2274 kJ/kg 2823.2 31 . 292 5 . 3115 1 4 out 2 3 in h h q h h q and the thermal efficiency of the cycle is 0.297 2 . 2823 . 1985 1 1 in out th q q 10-21E A simple steam Rankine cycle operates between the specified pressure limits. The mass flow rate, the power produced by the turbine, the rate of heat addition, and the thermal efficiency of the cycle are to be determined. Assumptions 1 Steady operating conditions exist. 2 Kinetic and potential energy changes are negligible. q 30 3 T Analysis From the steam tables (Tables A-4E, A-5E, and A-6E), Btu/lbm 18 . 77 46 . 7 72 . 69 Btu/lbm 46 . 7 ft psia 5.404 Btu 1 psia ) 1 2500 )( /lbm ft 01614 . ( ) ( /lbm ft 01614 ....
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Chapter_10 - Chapter 10 10-8C Heat rejected decreases;...

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