Carbon steel balls ( = 7830 kg/m 3 , k = 64 W/m K, c p

Carbon steel balls (ρ = 7830 kg/m³, k = 64 W/m · K, c_p = 434 J/kg · K) initially at 150°C are quenched in an oil bath at 20°C for a period of 3 minutes. If the balls have a diameter of 5 cm and the convection heat transfer coefficient is 450 W/m² · K. The center temperature of the balls after quenching will be.

(a) 27.4°C

(b) 143°C

(c) 12.7°C

(d) 48.2°C

(e) 76.9°C