A die cast component has a mass of 1.25 kg and density 7250 kg/m with surface area 0.08 m The component comes out of machine at 350°C and is exposed to air at 25°C with convective heat transfer coefficient 60 W/m' deg. Make calculations for the followings: (a) temperature of the component after 5 minutes, (b) time constant, (c) value of convective heat transfer coefficient upto which lumped parameter analysis is valid, and (d) value of volume/area ratio upto which the Tumped parameter model can be used. For the material of the component take, thermal conductivity = 100 W/m-deg and specific heat = 400 J/kg K.
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A metal piece of length I has a cross section of a sector of a circle of radius r and included angle of . Its two ends are maintained at temperatures t, and tz (t, > tz). Apply the respective governing equation for this case and find the expression for heat flow through the metal piece, assuming that conductivity of metal varies with temperature according to relation: k = ko (1 – Bt) = ae also assume that at at o and O and outer surfaces of the slab except ar the end surfaces are completely insulated. What will be the rate of heat transfer if I = 600 mm, r= 120 mm, 0 = 60°, tq = 125°C, t2 = 25°C, ko = 115 W/m°C and ß = 104
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A reactor's wall 320 mm thick, is made up of an inner layer of fire brick (k = 0.84 W/m°C) covered with a layer of insulation (k -0.16 W/m°C). The reactor operates at a temperature of 1325°C and the ambient temperature is 25°C. () Determine the thickness of fire brick and insulation where the interface temperature is 1200°C (ii) Calculate the heat loss
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A reactor's wall 320mm thick, is made up of an inner layer of fire brick (k = 0.84W/m°C) covered with a layer of insulation (k = 0.16W/m°C). The reactor operates at a temperature of 1325°C at the atmospheric temperature of 25°C. i. Calculate the thickness of brick and insulation. ii. Heat loss per unit area presuming that the insulating material has a maximum temperature of 1200°C.
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5 A surface at 300°C loses heat both by convection and radiation to the surroundings at 150°C. The convection coefficient is 75 W/m2K and the radiation factor due to geometric location and emissivity is 0.85. If the heat is conducted to the surface through a solid material of thermal conductivity 15 W/mK, determine the temperature gradient at the surface of the solid.
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