A 2-cm-high cylindrical ice block
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HEAT+MASS TRANSFER ACCESS CODE
- A 2-m × 1.8-m section of wall of an industrial furnace burning natural gas is not insulated, and the temperature at the outer surface of this section is measured to be 80°C. The temperature of the furnace room is 30°C, and the combined convection and radiation heat transfer coefficient at the surface of the outer furnace is 10 W/m2·C. It is proposed to insulate this section of the furnace wall with perlite insulation (k = 0.052 W/m·C) in order to reduce the heat loss by 90 percent, Assuming the outer surface temperature of the metal section still remains at about 80°C, determine the thickness of the insulation that needs to be used.arrow_forwardA 0.3-cm-thick, 12-cm-high, and 18-cm-long circuit board houses 80 closely spaced logic chips on one side,each dissipating 0.06 W. The board is impregnated with copper fillings and has an effective thermalconductivity of 16 W/m · °C. All the heat generated in the chips is conducted across the circuit board andis dissipated from the back side of the board to the ambient air at 30°C, which is forced to flow over thesurface by a fan at a free-stream velocity of 400 m/min. Determine the temperatures on the two sides ofthe circuit board.arrow_forwardConsider a person standing in a breezy room at 20°C. Determine the total rate of heat transfer from this person if the exposed surface area and the average outer surface temperature of the person are 1.6 m2 and 29°C, respectively, and the convection heat transfer coefficient is 6 W/m2 ·°C (Fig. 2–75).arrow_forward
- 1. A 1000-W iron is left on the iron board with its base exposed to the air at 20°C. The convection heat transfer coefficient between the base surface and the surrounding air is 35 W/m². °C. If the base has an emissivity of 0.6 and a surface area of 0.02 m², determine the temperature of the base of the iron. 2. The inner and outer surfaces of a 5-m x 6-m brick wall of thickness 30 cm and thermal conductivity 0.69 W/m °C are maintained at temperatures of 20°C and 5°C, respectively. Determine the rate of heat transfer through the wall, in W.arrow_forwardA 0.083-in-diameter electrical wire at 90°F is covered by 0.02-in-thick plastic insulation (k = 0.075 Btu/ h·ft·°F). The wire is exposed to a medium at 50°F, with a combined convection and radiation heat transfer coefficient of 2.5 Btu/h·ft2·°F. Determine if the plastic insulation on the wire will increase or decrease heat transfer from the wire.arrow_forwardThe wall of a house is 4-meter-high and 15 -meter- wide. The wall is constructed with a 9-cm thick outer layer of brick and a 5-cm inner layer of insulating material. On a cold day, the outer surface temperature of the wall is -5°C while the inner surface temperature is 24°C. The thermal conductivity of the brick is 0.80 W/m-K, while the thermal conductivity of the insulation is 0.03 W/m-K . both inner and outer and outer has transfeer coefficeint of 20 W/m2- K a. What is the total thermal resistance of the wal? b. What is the rate of heat loss through the walarrow_forward
- Consider a 1.2-m-high and 2-m-wide glass windowwith a thickness of 6 mm, thermal conductivity k = 0.78W/m·K, and emissivity « = 0.9. The room and the wallsthat face the window are maintained at 25°C, and the averagetemperature of the inner surface of the window is measuredto be 5°C. If the temperature of the outdoors is 25°C,determine (a) the convection heat transfer coefficient on theinner surface of the window, (b) the rate of total heat transferthrough the window, and (c) the combined natural convectionand radiation heat transfer coefficient on the outer surface ofthe window. Is it reasonable to neglect the thermal resistanceof the glass in this case?arrow_forward/ Hot square plate (1 m ×1 m) is to be cooled by attaching aluminum circular pin fins (D=0.25 cm, L= 3 cm) distributed with distance 0.6 cm as illustrated in Figs.(1-a) & (1-b). If the fin base temperature is 100°C, cooling air temperature is 30°C and h= 35 W/m. °C. Determine the total rate of heat transfer from the finned plate and the effectiveness of the fins? Assume k= 237 W/m.°C and nr=tanh mL/ mL.arrow_forwardConsider a 2-m-high electric hot-water heater thathas a diameter of 40 cm and maintains the hot water at 55°C.The tank is located in a small room whose average temperatureis 27°C, and the heat transfer coefficients on the innerand outer surfaces of the heater are 50 and 12 W/m2·K,respectively. The tank is placed in another 46-cm-diametersheet metal tank of negligible thickness, and the spacebetween the two tanks is filled with foam insulation (k =0.03 W/m·K). The thermal resistances of the water tank andthe outer thin sheet metal shell are very small and can be neglected. The price of electricity is $0.08/kWh, and the home owner pays $280 a year for water heating. Determine the fraction of the hot-water energy cost of this household that is due to the heat loss from the tank. Hot-water tank insulation kits consisting of 3-cm-thick fiberglass insulation (k = 0.035 W/m·K) large enough to wrap the entire tank are available in the market for about $30. If such an insulation is installed on…arrow_forward
- A cylindrical fuel rod of 2 cm in diameter is encased in a concentric tube and cooled by water. The fuel generates heat uniformly at a rate of 150 MW/m3. The convection heat transfer coefficient on the fuel rod is 5000 W/m2∙K, and the average temperature of the cooling water, sufficiently far from the fuel rod, is 70°C. Determine the surface temperature of the fuel rod and discuss whether the value of the given convection heat transfer coefficient on the fuel rod is reasonable.arrow_forwardThe roof of a house is electrically heated. This roof is 6 m long, 8 m highwide and 0.25 m thick, and is made with a flat layer of concrete whose conductivityis ? = 0.8 ?⁄? ?. The temperatures of the inner and outer surfaces are15 and 4 °C, respectively, for a period of 10 hrs. Determine a) the reason for the lossof heat through the roof that night and b) the cost of that heat loss to the homeownerof the house, if the cost of electricity is $0.08/kWh.arrow_forwardA 6 cm diameter sphere is initially at a temperature of 100C. Later, this sphere was thrown into water at 800C. Calculate how long it will take for the center temperature of the sphere to reach 500C by taking the convection heat transfer coefficient as 80W / m2K. Thermal properties of sphere material: k=0,627 W/moC a=0,151x10-6 m2/sarrow_forward
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