Ball bearing ro=4 mm leaving the oven at a uniform temperature of 900 oC are exposed to air for a while before they are dropped in to the water for quenching . Determine the time they can stand the air before their temperature falls below 850 oC also find the total rate of heat transfer .Take for the balls k = 54 W/m .oC , ρ= 7833 kg/m3 , Cp=0.456 kJ/kg.oC

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