A long iron rod (ρ = 7870 kg/m3 , cp = 447 J/kg · K, k = 80.2 W/m · K, and α = 23.1 × 10-6...

A long iron rod (ρ = 7870 kg/m3 , cp = 447 J/kg · K, k = 80.2 W/m · K, and α = 23.1 × 10-6 m2 /s) with diameter of 25 mm is initially heated to a uniform temperature of 700°C. The iron rod is then quenched in a large water bath that is maintained at constant temperature of 50°C and convection heat transfer coefficient of 128 W/m2 ·K. Determine the time required for the iron rod surface temperature to cool to 200°C.

FIGURE P 18-63