Consider a combined gas-steam power plant that has a net 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 stem cycle operates of 0.8 Mpa. The condenser pressure is 10 kPa. Assuming isentropic efficiencies of 100% for the pump, 82% for the compressor, and 86% for the gas and steam turbines, determine

i. the mass flow ratio of air to steam;

ii. the required rate of heat input in the combustion chamber, and

iii. the thermal efficiency of the combined.