Question

Consider the Rankine cycle below with steam flow rate of 5kg/s. The steam receives heat from the combustion gases in the furnace of the generator; assume the combustion gases change temperature from 2000°K to 425 K in flowing through the steam generator. The cooling water enters the condenser 20°C and leaves at 40°C. Assume the flow in the pump and the turbine is adiabatic and internally reversible. Also assume the combustion gas has the properties of air. If To is 20°C, determine the cycle irreversibility, I. The irreversibility I is give by: i = Σ(n3). Σ(hs ), + out T Question #2b) Show that the thermal efficiency of a combined gas-steam power plant cc can be expressed as: where nW and n W,IQu are the thermal efficiencies of the gas and steam cycles, respectively. Where Qin is the heat supplied to the gas cycle, where Qout is the heat rejected by the steam cycle, and where Qout is the heat rejected from the gas cycle and supplied to the steam cycle PP Heater Combustion gas Brayton gas turbine cycle (b) 425° K Gas turbine Compressor P2 8MPa 520 C T= m-5 kg/s 2000 K Air (a) Turbine Ww PP ww Fuel P-20 kPa 3 20° C Rankine steam cycle Condenser Cooling water Steam turbine 40 C Condenser PP oump Figure for Question 2a Figure for Question 2b

Answer 1

T Te Tapp ing Cycle Bat torm Cyele amd Omo 32(1-2) 3 (4-1) (34-1 ('41) -1 jn dOu,he overall ficiency could be here are (4-1) - (- (4) (1-p) (1-1) (- - 4 - To tal lors-Product ofstes in all he gyok far -1-(-k) -e) Proved

unithal erergy of the (h-h) y7-To)-Ti) 2g3 293x1.00 S S000- 593) 1.0o S 565.588 71 5.35 1149.947 K/K the 425 132109.56 23.144 K3/Kg ecteer in enry of pduet - 7 425 (2000 42s) 2g 3HoosX - 582.875- 656.24 g2462 K3/Kg Increase wates 303 293 CG 6 4g.497K5/Kタ Sporeversibi lity 5X92u? -5x49.4g7 4410.6125 KW