In the 1930s, the U. S. Navy operated dirigibles. The largest was the U. S.S. Akron with a length of 785 ft and a maximum diameter of 132 ft. Its maximum speed was 84 mph (123.2 ft/sec). Moving at top speed at 10,000 ft standard atmosphere, estimate the power required in horsepower to overcome the friction drag. Disregard effects of fins and other protrusions. Assume the surface of the dirigible is smooth and the friction drag is that over a flat plate. W=

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.