Question

P8-29 A closed feedwater heater is used in a Rankine cycle Steam leaves the boiler at 20 MPa, 600°C. Between the high and low-pressure turbines, steam at 1 MPa is extracted and delivered to the closed feedwater heater. Feedwater exits the feedwater heater at 20 MPa and the saturation temperature of the 1-MPa steam; saturated liquid condensate is fed through a steam trap back to the condenser. Steam from the second- stage turbine enters the condenser at 10 kPa, and saturated liquid exits the condenser. Both stages of the turbine have isen- tropic efficiencies of 90%, and the pump isentropic efficiency is 85%. a. Determine the fraction of steam entering the turbine that must be extracted b. etermine the net work per unit mass of steam entering the lirst turbine stage (in kJ/kg) c. Determine the heat added per unit mass of steam entering the first turbine stage (in kJ/kg) d. Determine the cyele thermal efficiency P 20 MPa T 600 C a90 % Boiler P-1.0 MPa 6P- 10 kPB Conderser Closed feedwater heater te85%

Answer 1

iven hi= 191.81 KI|kq v 000101 |K9 h2s= hitvi R)=191.81+0.0010l(20/000-10) Pi = 10 KPa O has212 KJlkg 7p-0-85as-h, h2-h R12-19.8 P 181bl-y A2-215.56 Ps 20MPa T3Tsat@IN Kslkg 3 haTT3 79-88'С (MPa P420MPa2b4=3539 KJ|9 TA 600 C S4 65015 K|k k P5IMPa 2 b=2141-9 KJ|kg D S4 S55J t=0.9-ha-hs , 3539- hs hr4-h5s 3539-2741-9 KsIkg-K hs-2821-6 KJ|kq, 5- 6 6811 Kalkg BP1O KPa hesR1576 S5= S65 PIMPa 2 h162.5/ хчо h718-1625 Kk9

T0.9 5-he 28216- h6 2821-6-211576 ドakg AFPly enngy alarxe 2186.34 CF WH On hs-h 773-21556 R821.6-162:51 J0.21 osteam entering teorbine, y=0-271 2O MPa 2 IMPa 2 fraction the loKPa bNet ork by turbine, (ha-h)(1-) (h5-h -C539-28216) + -o-21)(R81-6-2186.34) 805 K|kg Wp=hュ-b」 p23T5 KJ) kq Wイニ + WT 15 56-191-8I Heat addition, 9in =h4-thg = d539-773 n2166 Kkg d) ycle thermal ficieny WT WP 11805-2375 2766 Mth= 418