EGR 334 Homework Solutions HW Set32

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EGR 334         HW Set32_

Problem 8: 21

The figure provides steady state operating data for a vapor power plant using water as the working fluid. The mass flow rate of water is 12 kg/s. The turbine and pump operate adiabatically but not reversibly. Determine

  1. a) the thermal efficiency
  2. b) the rates of heat transfer Qin dot and Qoutdot each in kW.

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EGR 334         HW Set32

Problem 8: 29

Water is the working fluid in an ideal Rankine cycle with reheat. Superheated vapor enters the turbine at 10 MPa, 480 C and the condenser pressure is 6 kPa. Steam expands through the first stage turbine to 0.7 MPa and then is reheated to 480 C. Determine for the cycle

  1. a) the rate of heat addition in kJ per kg of steam entering the first stage turbine.
  2. b) the thermal efficiency.
  3. c) the rate of heat transfer from the working fluid passing through the condenser to the cooling water in kJ per kg of steam entering the first stage turbine.

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EGR 334         HW Set32_

Problem 8: 49

Water is the working fluid in an ideal regenerative Rankine cycle with one closed feedwater heater. Superheated vapor enters the turbine at 10 MPa, 480 C and the condenser pressure is 6 kPa. Steam expands through the first stage turbine where some is extracted and diverted to a closed feedwater heater at 0.7 MPa. Condensate drains from the feedwater heater as saturated liquid at 0.7 MPa and is trapped into the condenser. The feedwater leaves the heater at 10 MPa and a temperature equal to the saturation temperature at 0.7 MPa. Determine for the cycle.

  1. a) the rate of heat transfer to the working fluid passing through the steam generator in kJ per kg of steam entering the first stage turbine.
  2. b) the thermal efficiency
  3. c) the rate of heat transfer from the working fluid passing through the condenser to the cooling water in kJ per kg of steam entering the first stage turbine.

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EGR 334         HW Set32_

Problem 8: 60

Consider a regenerative vapor power cycle with two feedwater heaters, a closed one and an open one as shown in the figure. Steam enters the first turbine stage at 12 MPa, 480 C and expands to 2 MPa. Some steam is extracted at 2 MPa and fed to the closed feedwater heater. The remainder expands through the second stage turbine to 0.3 MPa where an additional amount is extracted and fed into the open feedwater heater operating at 0.3 MPa. The steam expanding through the third stage turbine exits at the condenser pressure of 6 kPa.

Feedwater leaves the closed heater at 210 C, 12 MPa, and condensate exiting as saturated liquid at 2 MPa is trapped into the open feedwater heater. Saturated liquid at 0.3 MPa leaves the open feedwater heater. Assume all pumps and turbine stages operate isentropically. Determine for the cycle

  1. a) the rate of heat transfer to the working fluid passing through the steam generator, in kJ per kg of steam entering the first stage turbine.
  2. b) the thermal efficiency.
  3. c) the rate of heat transfer from the working fluid passing through the condenser to the cooling water in kJ per kg of steam entering the first stage turbine.
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