An uncoated, solid cable of length L = 1m and diameter D = 40 mm is exposed to convection conditions characterized by h = 55 W/m2 ·K and T[infinity] = 20°C. Determine the maximum electric current that ca be carried by the cable if it is pure copper, pure aluminum, or pure tin. Calculate the minimum wire temperatures. The electrical resistivity is Re = 10 x 10-8 Ω·m for copper and aluminum at their melting points, while the electrical resistivity of tin is Re = 20 x 10-8 Ω·m at its melting point

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.