12mm diameter Steel balls are annealed by heating to 1150 K and then slowly cooling to 400K in an air environment for which T 00 = 325 K and h=20 W/m² K. If the properties of the steel are k = 40 W/m K, p= 7800 kg/ m° and c, = 600 J/kg-K, what will be the d. time required for the cooling process? A 17 min B 19 min C 16 min D 15 min

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6. a. The heat flux applied to the walls of the biomass combustion furnace is 20 W/m2. The furnace walls have a thickness of 10 mm and a thermal conductivity of 12 W/m.K. If the wall surface temperature is measured to be 50oC on the left and 30oC on the right, prove that conduction heat transfer occurs at a steady state!b. Heating the iron cylinder on the bottom side is done by placing the iron on the hotplate. This iron has a length of 20 cm. The surface temperature of the hotplate is set at 300oC while the top side of the iron is in contact with the still outside air. To reach the desired hotplate temperature, it takes 5 minutes. Then it takes 15 minutes to measure the temperature of the upper side of the iron cylinder at 300oC. Show 3 proofs that heat transfer occurs transiently

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