A 314 grade stainless steel sphere with a diameter of 500 mm is coated with a dielectric material layer of thickness 4 mm and thermal conductivity 0.025 W/m*K. After coating, the sphere is initially at a uniform temperature of 600C and then its quenched in ana oil bath with T=80 C and h=3500 W/m. Calculate the time required for the shere temperature to reach 1000C

Note 1 Explain why the thermal resistance for a conduction through a wall can be used in this case.

Note 2 Prove that lumped capacitance method is applicable here.

Properties of stainless steel at 350C: p=7850kg/m^3, C=570 J/kg*K, k=50W/m*K