Asteel sphere with a diameter of 7.6 cm is to be hardened by first heating it to a uniform temperature of 870c and then quenching it in a large bath of water maintained at a temperature of 38c. the fluid motion in the quenching bath is such that it produces a convective heat transfer coefficient of h = 566 w/m2 · k. determine (a) the time required to cool the center of the sphere to 204c, and (b) the elapsed time when the surface of the sphere has cooled to 750c. and property values: k = 43 w/m · k, cp = 628 j/kg k, and = 7840 kg/m3 .