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2010quiz7 - Solution Find Total Enthalpy change for steam...

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Center for Advanced Energy Systems Michael R. Muller, Director 640 Bartholomew Road, Piscataway NJ 08854 (908) 655-8469 FAX: (732) 445-0730 [email protected] http://caes.rutgers.edu 650:462 Power Plants Quiz 7 NAME: __________________________ Open book November 15, 2010 Consider a single pressure HRSG attached to a gas turbine which exhausts 212 lbm/min into the HRSG at 941°F. If the 15 lbm/min of water at 300 psia enters the HRSG at 100°F and leaves at 700 °F, what are the pinch point temperature difference and the temperature of the air leaving the HRSG? Use Air Tables or Constant Specific Heats – Your choice! BUT – don’t mix them, use either one scheme or the other!!!
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Unformatted text preview: Solution: Find Total Enthalpy change for steam hin = 68.79 Btu/lbm and hout = 1368.9 Btu/lbm Enthalpy for saturated liquid = 394 Btu/lbm (sat temp = 417.35 °F) Given the flow rate, total energy transfer is: 19,501 Btu/min For air side, with given mass flow rate, total change in enthalpy should be: 91.98 Btu/lbm Inlet enthalpy = 342.9 Btu/lbm Exit enthalpy = 250.95 - exit air temp = 581 °F Pinch Point occurs where water starts to boil. Enthalpy difference there is 1368.9-394 = 974.9 Btu/lbm or 14623 Btu/min For Air – this means a drop in enthalpy of 14623/212 = 68.98 or an enthalpy of 342.9-68.98 = 273.92 Btu/lbm – or a temp of approx 669 °F Pinchpoint = 669-417.35= 251.65 °F...
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