Consider a combined gas-steam power plant that has a net power output of 280 MW. The pressure ratio of the gas-turbine cycle is 11. Air enters the compressor at 300 K and the turbine at 1100 K. The combustion gases leaving the gas turbine are used to heat the steam at 5 MPa to 350°C in a heat exchanger. The combustion gases leave the heat exchanger at 420 K. An open feedwater heater incorporated with the steam cycle operates at a pressure of 0.8 MPa. The condenser pressure is 10 kPa. Assuming isentropic efficiences of 100 percent for the pump, 82 percent for the compressor, and 86 percent for the gas and steam turbines, determine (
a) the mass flow rate ratio of air to steam,
b. ) the required rate of heat input in the combustion chamber, and (
c. ) the thermal efficiency of the combined cycle.