Find the solidification time of the two iron castings when both are poured (with no superheats) into the sand molds at initial temperature 28°C.

(i) A slab shaped casting of 10 cm thickness, (ii) a sphere of 10 cm in dia. Iron: freezing temp: 1540°C; L= 272 kJ/kg; density = 7850 kg/m3 Sand: c = 1.17 kJ/kg-K; k = 0.865 W/mk; density = 1600 kg/m3

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.