For Problem 9.134, determine the change in exergy of the water flow and that of the air flow. Use these values to determine the second-law efficiency of the boiler heat exchanger.
Problem 9.134
A Rankine steam power plant should operate with a high pressure of 3 MPa and a low pressure of 10 kPa, and the boiler exit temperature should be 500?C. The available high-temperature source is the exhaust of 175 kg/s air at 600?C from a gas turbine. If the boiler operates as a counter flowing heat exchanger in which the temperature difference at the pinch point is 20?C, find the maximum water mass flow rate possible and the air exit temperature.