A copper sphere weighing 3 kg is heated in a furnace to a temperature of 300°C and is suddenly taken out and allowed to cool in ambient air at 25° C.
If it takes 60 min for the copper sphere to cool down to 35°C, what is the average surface heat transfer coefficient? Take density of copper sphere r= 8950 kg/m3 and specific heat cP = 0.383 kJ/kg°C.
State the assumptions made and derive the relation used.