A circular air-conditioning duct carries cool air at 5oC and is constructed of 1 percent carbon steel with a thickness of 0.2 mm and an outside diameter of 18 cm. The duct is in a horizontal position and gains heat from room air at 20oC. If the average air velocity in the duct is 7.5 m/s, estimate the air temperature rise in a duct run of 30 m. Be sure to state your assumptions in arriving at an answer.