Property Data Use in the Closed System Energy Balance Example A piston cylinder assembly contains 2 kg of water at 100oC and 1 bar The water is compressed to a saturated vapor state where the pressure is 2 5 bar During compression there is a heat transfer of energy from the water to its surroundings having a magnitude of 250 kJ Neglecting changes in kinetic energy and potential energy determine the work in kJ for the process of the water T State 1 T1 100oC p1 1 bar State 2 2 kg of water Q 250 kJ Saturated vapor p2 2 5 bar p2 2 5 bar 2 T1 100oC p1 1 bar 1 v Property Data Use in the Closed System Energy Balance Solution An energy balance for the closed system is 0 0 DKE DPE DU Q W where the kinetic and potential energy changes are neglected Thus W Q m u2 u1 State 1 is in the superheated vapor region and is fixed by p1 1 bar and T1 100oC From Table A 4 u1 2506 7 kJ kg State 2 is saturated vapor at p2 2 5 bar From Table A 3 u2 ug 2537 2 kJ kg W 250 kJ 2 kg 2537 2 2506 7 kJ kg 311 kJ The negative sign indicates work is done on the system as expected for a compression process
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