Problem 9-2 - Example 9-2 Saturated water at 15 kPa enters...

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Example 9-2 Saturated water at 15 kPa enters the pump in an ideal reheat Rankine cycle. It is pumped to 25 MPa and heated in a boiler to 700°C. After expansion through the first- stage turbine, the steam pressure is reduced to 6MPa. The steam is reheated to 700°C and expanded in the second-stage turbine. If the power output desired is 400 MW, find the mass flow rate. Estimate the cycle efficiency assuming pump work is negligible. Solution: Define a control volume around the boiler and reheater. The first law for this control volume is ee ii QW m h m h −= ± ± ±± ei mmm == ±±± Since there is no work and the total heat added to the cycle is the sum of the heat in the boiler and reheater () 3524 H Qm h h h h =+ ± ± To find h 2 , we will have to work our way across the pump. At the pump inlet 1 kJ enthalpy(steam, 0, 15) 226 kg hx P = = ( ) 21 P Wm h h m v P P =− = ± 3 m volume(steam, 0, 15) 0.001014 kg vx P = = hh v P P 3 2 kJ m 226 0.001014 25000 15 kPa kg kg h ⎛⎞ ⎜⎟ ⎝⎠
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2 kJ 251.2 kg h = 3 kJ enthalpy(steam, 700, 25000) 3773 kg hT P == = = To find h 4 , consider the second law for the first stage turbine
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Problem 9-2 - Example 9-2 Saturated water at 15 kPa enters...

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