Consider a small diffuse surface of area A1 = 1 cm2 with a total emissive power of 50000 W/m2. Another small surface of area A2 = 5 cm2 is located at a distance of r = 50 cm from A1 at an angle of θ1 = 60° w. r.t to the normal of A1. The line joining the two surfaces is at an angle of θ2 = 30° w. r.t to the normal of A2.

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.