# EGR 334 Homework solutions HW Set 26

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EGR 334         HW Set 26

Problem 6: 80

A gas flows through a 1-inlet, 1-outlet control volume operating at steady state. Heat transfer at the rate Qdotcv takes place only at a location on the boundary where the temperature is Tb. For each of the following cases, determine whether the specific entropy of the gas at the exit is greater than, equal to, or less than the specific entropy of the gas at the inlet.

1. a) no internal irreversibilities, Qdotcv = 0
2. b) no internal irreversibilities, Qdotcv < 0
3. c) no internal irreversibilities, Qdotcv > 0
4. d) no internal irreversibilities, Qdotcv >= 0

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EGR 334         HW Set 26

Problem 6:86

By injecting liquid water into superheated steam, the desuperheater shown has a saturated vapor stream at its exit. Steady state operating data are provided in the accompanying table. Stray heat transfer and all kinetic and potential energy effect are negligible. a) Locate states 1, 2, nd 3 on a sketch on the T-s diagram. b) Determine the rate of entropy production within the desuperheater in kW/K.

 State p(MPa) T(deg C) v(m3/kg) u(kJ/kg) h(kJ/kg) s(kJ/kg-K) 1 2.7 40 0.0010066 167.2 169.9 0.5714 2 2.7 300 0.09101 2757.0 3002.8 6.6001 3 2.5 sat. vapor 0.07998 2603.1 2803.1 6.2575

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EGR 334         HW Set 26

Problem 6:91

Steam at 240 deg C and 700 kPa enters an open feedwater heater operating at steady state with a mass flow rate of 0.5 kg/s. A separate stream of liquid water enters at 45 deg C, 700 kPa with a mass flow rate of 4 kg/s. A single mixed stream exits at 700 kPa and temperature T. Stray heat transfer and KE and PE can be ignored. Determine

1. a) T, in deg C and
2. b) the rate of entropy production within the feedwater heater in kW/K.
3. c) Locate the three principal states on a sketch of the T-s diagram.

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EGR 334         HW Set 26

Problem 6: 111

The figure show data for a portion of the ducting in a ventilation system operating at steady state. The ducts are well insulated and the pressure is very nearly 1 atm throughout. Assuming the ideal gas law for air with cp = 0.24 Btu/lb-R and ignoring KE and PE, determine

1. a) the temperature of the air at the exit in deg F.
2. b) the exit diameter in ft
3. c) the rate of entropy production within the duct in Btu/min-R.

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