Repeat Problem 7.9 if the extrusion cross-section is elliptical with the major axis normal to the air flow and the same mass per unit length. The major axis of the elliptical cross section is 5.46 cm, and its perimeter is 12.8 cm.
Problem 7.9
A long, hexagonal copper extrusion is removed from a heat-treatment oven at 400°C and immersed in a 50°C airstream flowing perpendicular to its axis at 10 m/s. The surface of the copper has an emissivity of 0.9 due to oxidation. The rod is 3 cm across opposing flat sides and has a cross-sectional area of 7.79 cm2 and a perimeter of 10.4 cm. Determine the time required for the center of the copper to cool to 100°C.
