A spherical object with diameter D $,$ thermal conductivity k $,$ and thermal diffusivity $$ is initially at a uniform temperature $T_i.$ The object is submerged in a hot fluid at temperature $T_{},$ with a convection heat transfer coefficient $h$ at the surface. Illustrate the geometric shape and coordinate system you will use. Clearly outline the conditions and simplifications you are making. Formulate the differential equation and specify the initial and boundary conditions necessary to describe the temperature distribution within the sphere. Do not solve the equation.