Thermodynamics

450 | ThermodynamicsThat is, if the process between states 1 and 2 were executed in a reversiblemanner, the system would deliver 9.6 kJ of useful work.(c) The total exergy destroyed during this process can be determined fromthe exergy balance applied on the extended system (system + immediatesurroundings) whose boundary is at the environment temperature of T 0 (sothat there is no exergy transfer accompanying heat transfer to or from theenvironment),Net exergy transfer Exergy Changeby heat, work, and mass destruction in exergywhere W u,out is the useful boundary work delivered as the system expands. Bywriting an energy balance on the system, the total boundary work done duringthe process is determined to beNet energy transferby heat, work, and massChange in internal, kinetic,potential, etc., energiesThis is the total boundary work done by the system, including the work doneagainst the atmosphere to push the atmospheric air out of the way duringthe expansion process. The useful work is the difference between the two: 5.3 kJE in E out ¢E systemQ out W b,out ¢UW u W W surr W b,out P 0 1V 2 V 1 2 W b,out P 0 m 1v 2 v 1 2 8.8 kJ 1100 kPa2 10.05 kg2310.9599 0.257992 m 3 1 kJ>kg4a1 kPa # b m3Substituting, the exergy destroyed is determined to beX destroyed X 1 X 2 W u,out 35.0 25.4 5.3 4.3 kJThat is, 4.3 kJ of work potential is wasted during this process. In otherwords, an additional 4.3 kJ of energy could have been converted to workduring this process, but was not.The exergy destroyed could also be determined fromX destroyed T 0 S gen T 0 c m 1s 2 s 1 2 Q surrdT 0 1298 K2e10.05 kg2317.2810 7.12462 kJ>kg # K4 4.3 kJX in X out X destroyed ¢X systemW b,out Q out ¢U Q out m 1u 2 u 1 2 8.8 kJ⎫ ⎪⎬⎪⎭⎫⎪⎬⎪⎭⎫⎪⎬⎪⎭⎫ ⎪⎬⎪⎭⎫⎪⎬⎪⎭X work,out X heat,out ¡0 X destroyed X 2 X 1which is the same result obtained before.X destroyed X 1 X 2 W u,out12 kJ2 10.05 kg212577.1 2793.72 kJ>kg2 kJ298 K f