Chapter 10.9, Problem 112RP

Show that the thermal efficiency of a combined gas–steam power plant ηcc can be expressed as

${\eta }_{\infty }={\eta }_g+{\eta }_s-{\eta }_g{\eta }_s$

where ηg = Wg /Qin and η_s = W_s/Q_g,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.