A long steel rod (2 cm in diameter, 2 m long) has been heat-treated and quenched to a temperature of 100°C in an oil bath. In order to cool the rod further it is necessary to remove it from the bath and expose it to room air. Will the faster cool-down result from cooling the cylinder in the vertical or horizontal position? How long will the two methods require to allow the rod to cool to 40°C in 20°C air?
GIVEN
A long steel rod in air
Diameter (D) = 2 cm = 0.02 m
Length (L) = 2 m
Initial temperature (Ts,i) = 100°C
Air temperature (T∞) = 20°C
ASSUMPTIONS
Steel is 1% carbon