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2010quiz3

# 2010quiz3 - Gift from Professor Muller to save y’all work...

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Center for Advanced Energy Systems Michael R. Muller, Director 640 Bartholomew Road, Piscataway NJ 08854 (732) 445-3655 FAX: (732) 445-0730 [email protected] http://caes.rutgers.edu 650:462 Power Plants Quiz 3 NAME: __________________________ Open book October 12, 2010 Mixing is an irreversible event and thereby should create entropy. Consider the entropy production in an open feedwater heater. In this case 60 kg/min of liquid from the condensor is pumped from 20 kPa to 7 mPa and enters the feedwater heater at 22 °C and is mixed with steam tapped (at 7 mPa) from a turbine. The steam is superheated by 114 °C. a) Find the enthalpy of the steam b) Find the mass flow rate of steam needed to create saturated liquid at the exit of the feedwater heater c) Find the change in entropy caused by the mixing

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Unformatted text preview: Gift from Professor Muller: to save y’all work, the enthalpy of the water entering the feedwater heater is 92.27 kJ/kg and the entropy is 0.3249 kJ/kg-K Solution: a) 0.1 mPa = 1 bar 1 bar = 100 kPa 7 mPa, = 70 bar - saturation temperature = 285.9 °C …. superheated temp = 400 °C Enthalpy = 3158.1 kJ/kg; entropy = 6.4478 kJ/kg-K b) After the pump, h = 92.27 kJ/kg, entropy = 0.3249 kJ/kg-K For saturated liquid, s= 3.1216 h = 1267.4 60 * 92.27 + X * 3158.1 = (60 +X) * 1267.4 (3158.1 – 1267.4) X = 70,507.8 X = 37.29 kg/min Center for Advanced Energy Systems Michael R. Muller, Director C) entropy in = 60*0.3249 + 37.29* 6.4478 = 259.93 kJ/K Entropy 0ut = 97.29* 3.1216 = 303.70 Entropy production = 43.77 kJ/min-K...
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2010quiz3 - Gift from Professor Muller to save y’all work...

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