The gas-turbine portion of a combined gas-steam power plant has a pressure ratio of 16. Air enters the compressor at 300 K at a rate of 14 kg/s and is heated to 1500 K in the combustion chamber. The combustion gases leaving the gas turbine are used to heat the steam to $400^{\circ} \mathrm{C}$ at 10 MPa in a heat exchanger. The combustion gases leave the heat exchanger at at 420 K. The steam leaving the turbine is condensed at 15 kPa. Assuming all the compression and expansion processes to be isentropic, determine (a) the mass flow rate of the steam. (b) the net power output, and (c) the thermal efficiency of the combined cycle. For air, assume constant specific heats at room temperature.

Consider a combined gas–steam power plant that has a net power output of 450 MW. The pressure ratio of the gas-turbine cycle is 14. Air enters the compressor at 300 K and the turbine at 1400 K. The combustion gases leaving the gas turbine are used to heat the steam at 8 MPa to 4008C in a heat exchanger. The combustion gases leave the heat exchanger at 460 K. An open feedwater heater incorporated with the steam cycle operates at a pressure of 0.6 MPa. The condenser pressure is 20 kPa. Assuming all the compression and expansion processes to be isentropic, determine (a) the mass flow rate ration of air to steam, (b) the required rate of heat input in the combustion chamber, and (c) thermal efficiency of the combined cycle.

The gas-turbine cycle of a combined gas-steam power plant has a pressure ratio of 12. Air enters the compressor at 310 K and the turbine at 1400 K. The combustion gases leaving the gas turbine are used to heat the steam at 12.5 MPa to $500^{\circ} \mathrm{C}$ in a heat exchanger. The combustion gases leave the heat exchanger at $247^{\circ} \mathrm{C}.$ Steam expands in a high-pressure turbine to a pressure of 2.5 MPa and is reheated in the combustion chamber to $550^{\circ} \mathrm{C}$ before it expands in a low-pressure turbine to 10 kPa. The mass flow rate of steam is 12 kg/s. Assuming all the compression and expansion processes to be isentropic, determine (a) the mass flow rate of air in the gas-turbine cycle, (b) the rate of total heat input, and (c) the thermal efficiency of the combined cycle.

Show that the thermal efficiency of a combined gas-steam power plant $\eta_{cc}$ can be expressed as $\eta_{cc}=\eta_{g}+\eta_{s}-\eta_{g}\eta_{s}$ where $\eta_{g}=W_{g} / Q_{\text {in}}$ and $\eta_{s}=W_{s} / Q_{\text {R.out}}$ are the thermal efficiencies of the gas and steam cycles, respectively. Using this relation, determine the thermal efficiency of a combined power cycle that consists of a topping gas-turbine cycle with an efficiency of 40 percent and a bottoming steam-turbine cycle with an efficiency of 30 percent.

A steam power plant operates on an ideal reheat-regenerative Rankine cycle. Steam enters the high-pressure turbine at 10 MPa and $550^{\circ} \mathrm{C}$ and leaves at 0.8 MPa. Some steam is extracted at this pressure to heat the feedwater in an open feedwater heater. The rest of the steam is reheated to $500^{\circ} \mathrm{C}$ and is expanded in the low-pressure turbine to the condenser pressure of 10 kPa. Determine the exergy destruction associated with the reheating and regeneration processes. Assume a source temperature of 1800 K and a sink temperature of 290 K.