Awell-insulated rigid tank contains 3 kg of saturated liquid-vapor mixture of water at 250 kpa. initially, three-quar- ters of the mass is in the liquid phase. an electric resistance heater placed in the tank is turned on and kept on until all the liquid in the tank is vaporized. assuming the surroundings to be at 25°c and 100 kpa, determine (a) the exergy destruction and (b) the second-law efficiency for this process.

Along 8-cm diameter steam pipe whose external surface temperature is 900c connects two buildings. the pipe is exposed to ambient air at 70c with a wind speed of 50 km/hr blowing across the pipe. determine the heat loss from the pipe per unit length. (b) air at 500c enters a section of a rectangular duct (15 cm x 20 cm) at an average velocity of 7 m/s. if the walls of the duct are maintained at 100c. a) the length of the tube for an exit temperature of the air to be 40 0c. b)the rate of heat transfer from the air. c) the fan power needed to overcome the pressure drop in this section of the duct.