Air at 1 atm and 38oC is forced through a horizontal 6.5-mm-diameter tube at an average velocity

Question:

Air at 1 atm and 38oC is forced through a horizontal 6.5-mm-diameter tube at an average velocity of 30 m/s. The tube wall is maintained at 540oC, and the tube is 30 cm long. Calculate the average heat-transfer coefficient. Repeat for a velocity of 30 m/s and a tube wall temperature of 800oC.