In the boiler of a power plant are tubes through which water flows as it is brought from a saturated liquid condition at 1000 lbf/in.2 to 1300°F at essentially constant pressure. Combustion gases passing over the tubes cool from 1740°F to temperature T at essentially constant pressure. The mass flow rates of the water and combustion gases are 400 and 2995.1 lb/s, respectively. The combustion gases can be modeled as air behaving as an ideal gas. There is no significant heat transfer from the boiler to its surroundings. Assuming steady state and neglecting the effects of motion and gravity, determine

(a) the exit temperature T of the combustion gases, in °F.

(b) the exergy destruction rate, in Btu/s.

(c) the exergetic efficiency given by Eq. 7.27. Let T0 5 50°F, p0 5 1 atm.