Ciclo Rankine

examen

Equations
Consider an ideal steam regenerative Rankine cycle with two feedwater heaters, one closed and one open. Steam enters the turbine at 10 MPa and 500 C and exhausts to the condenserat 10 kPa. Steam is extracted from the turbine at 0.7 MPa for the closed feedwater heater and 0.3 MPa for the open one. The extracted steam leaves the closed feedwater heater and is subsequentlythrottled to the open feedwater heater. Show the cycle on a T-s diagram with respect to saturation lines, and using only the data presented in the data tables given below determine: a) the fraction ofsteam leaving the boiler that is extracted at 0.3 MPa z=0.1425 b) the fraction of steam leaving the boiler that is extracted at 0.7 MPa y=0.06213 c) the heat transfer from the condenser per unit massleaving the boiler qout =1509 kJ/kg d) the heat transfer to the boiler per unit mass leaving the boiler qin =2677 kJ/kg e) the mass flow rate of steam through the boiler for a net power output of 250 MWm=214.1 kg/s ˙ f) the thermal efficiency of the cycle. η th =0.4363 DATOS x1 = 0 P7 = 300 [kPa] P8 = 10000 [kPa] P9 = 700 [kPa] P11 = 10 [kPa] Con estas presiones podemos optener las temperaturas desaturacion con sus respectivos volumenes Tsat;8 = Tsat (Steam; P = P8 ) Tsat;7 = Tsat (Steam; P = P7 ) Tsat;9 = Tsat (Steam; P = P9 ) Tsat;11 = Tsat (Steam; P = P11 ) v8 = v (Steam; T = Tsat;8 ; x = x1 )v7 = v (Steam; T = Tsat;7 ; x = x1 ) v9 = v (Steam; T = Tsat;9 ; x = x1 ) v11 = v (Steam; T = Tsat;11 ; x = x1 ) v3 = v7 (6) (7) (8) (9) (10) (11) (12) (13) (14) (1) (2) (3) (4) (5)

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Como esun ciclo Rankine las bombas y turbina, son isentropicas; y no hay caidas de presi´ n en la caldera, el condensador o y los calentadores por lo tanto se tiene que: P1 = P11 P2 = P7 P3 = P7 P4 = P8 P5 =P8 P6 = P9 P10 = P7 h8 = h (Steam; T = 500; P = P8 ) s8 = s (Steam; T = 500; P = P8 ) Dado que en las turbinas y bombas son isentropicas: s9 = s8 s10 = s8 s11 = s8 Con las entropias anteriores...