Along 8-cm diameter steam pipe whose external surface temperature is 90°c 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 50°c 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 10°c, determine (i) the length of the tube for an exit temperature of air to be 40 °c (ii) the rate of heat transfer from the air and (iii) the fan power needed to overcome the pressure drop in this section of the duct.