A metal sphere 20 mm radius at 90 K is allowed to cool in a room at 310 K by (a) convection only, (b) radiation only. Determine in each case the time required for the sphere to reach 450 K. Take density = 2700 kg/m3, specific heat = 1110 J/kgK, conductivity = 218 W/mK, heat transfer coefficient 18 W/m2K.
Hints: (a) Solve by lumped parameter model.
(b) Cooling by radiation, as in the previous problem
Negative sign is being used due to cooling.
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