2. A steel sphere (AISI 1010), 100mm in diameter, is coated with a dielectric material layer of thickness 2mm and thermal conductivity 0.04W/mK. The coated sphere is initially at a uniform temperature of 500C and is suddenly quenched in a large oil bath for which T=100 C and h=3000W/m2K. Note: Use thermal properties of steel from Table A.1 (k and cp @, 600K, at 300K). (a) Estimate the time require for the coated sphere temperature to reach 150C. Hint: Neglect the effect of energy storage in the dielectric material, since its thermal capacitance (cV) is small compared to that of the steel sphere. (b) Repeat your calculation in part (a) for the bare sphere with no dielectric coating (still assume lumped capacitance model)