Calculate the exergy associated with the drum of an industrial steam boiler that is shutting down. Assume all the mass flow rates of water in and out of the drum are negligible. The environment is at T₀ = 293 K and 1 atm. The drum is at 15 m height, and its water at 12.4 MPa in saturated conditions, and half of its volume is occupied by liquid. The drum diameter is 1.5 m and its length 5 m. Which is its largest form of exergy? What should be the height of the drum for its potential exergy to equal its physical exergy?