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Question: a rankine cycle operates with and without a feedwater heater...

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A Rankine cycle operates with and without a feedwater heater. Pressure of the steam at the inlet is 8 MPa and T= 440 C. Pressure of the condenser is 0.006 MPa. The steam expands to 0.6 MPa after the 1st-stage turbine and a certain percentage of steam is turned into an open feedwater heater of pressure 0.6 MPa. At the exit of the feedwater heater, Saturated liquid is at 0.6 MPa. The rest of the steam expands after 2nd-stage turbine and streams to the condenser that is operated at 0.006 MPa. The 1st-stage turbine, 2nd-stage turbine, and pump have 80% isentropic efficiency.

  • Find the thermal efficiency without the feedwater heater (Hint: mass flow at state 2 is zero and treat the two pumps as one pump).
  • Find the heat added to the boiler (kJ/kg) without the feedwater heater.
  • Find the thermal efficiency with the feedwater heater.
  • Find the heat added to the boiler with the feedwater heater (kJ/kg).

Power output Turbine Boiler 2 Condenser Heater 6 Pump Pump

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