A gas turbine plant consists of a compressor with a pressureratio of 10, a combustion chamber, and a turbine mounted on thesame shaft as the compressor; the net electrical power of the unitis 20 MW. The inlet air conditions are 1.013 bar and 15 ?C and themaximum cycle temperature is 1100 K. The exhaust gases from theturbine are passed through a heat exchanger to heat water for spaceheating before passing to the chimney; by this means water at 60 ?Cflowing at a rate of 2×106 kg/h is heated to 80 ?C. Using thefurther data below and neglecting the mass flow rate of fuel,calculate; (i) the temperature of the gases leaving theturbine;
(ii) the mass flow rate of air entering the unit;
(iii) the temperature of the gases entering the chimney;
(iv) the overall efficiency of the system defined as the usefulenergy output divided by the energy input from the fuel. Combinedmechanical and electrical efficiency of gas turbine unit, 90 %;combustion efficiency, 99 %; isentropic efficiency of aircompressor, 80 %; isentropic efficiency of gas turbine, 83 %;pressure drop in combustion chamber, 0.20 bar; pressure drop ofgases in heat exchanger, 0.15 bar; pressure drop in chimney, 0.05bar; specific heat capacity and ? of combustion gases, 1.15 kJ/kg Kand 4/3; mean specific heat capacity of water, 4.191 kJ/kg K.
ANSWER (453.8 ?C; 240 kg/s; 285 ?C; 50 %)
