A thick wall made of refractory bricks
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Heat And Mass Transfer
- 2.55 A long, 1-cm-diameter electric copper cable is embedded in the center of a 25-cm-square concrete block. If the outside temperature of the concrete is 25oC and the rate of electrical energy dissipation in the cable is 150 W per meter length, determine temperatures at the outer surface and at the center of the cable.arrow_forwardA 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_forwardA 2.5-cm-thick sheet of plastic initially at 20oC is placed between two heated steel plates that are maintained at 140oC. The plastic is to be heated just long enough for its mid-plane temperature to reach 130oC. If the thermal conductivity of the plastic is 1.2 x 10 -3 W/m/K, the thermal diffusivity is 2.7 x 10 -6 m2/s, and the thermal resistance at the interface between the plates and the plastic is negligible, determine a) the required heating time, b) the temperature at a plane 0.6 cm from the steel plate at the moment the heating is discontinued, and c) the time required of the plastic to reach the temperature of 130oC at 0.6 cm from the steel plate.arrow_forward
- 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 2 m X 1.5 m section of wall of an industrial furnace burning gas is not insulated, and the temperature at the outer surface of this section is measured to be 80oC. The temperature of the furnace room is 30oC, and the combined convection and radiation heat transfer coefficient at the surface of the outer furnace is 10 w/oC. It is proposed to insulate this section of the furnace wall with glass wool insulation (K=0.038 W/moC) in order to reduce the heat loss by 90 percent. Assuming the outer surface temperature of the section remains at about 80oC, determine i) the thickness of the insulation that is needed and ii) the outer surface temperature of the insulation after installation.arrow_forwardConsider hotdog being cooked in boiling water in a pan. Would the heat transfer be modeled as one-dimensional or two-dimensional? Would the heat transfer be steady or transient? Explain.arrow_forward
- A person puts a few apples into the freezer at 15°C cool them quickly for guestswho are about to arrive. Initially, the apples are at a uniform temperature of 20°C,and the heat transfer coefficient on the surfaces is 8 W/m2·K. Treating the apples as9-cm-diameter spheres and taking their properties to be 840 kg/m3, Cp 3.81 kJ/kg·K, k = 0.418 W/m·K, and α =10-7 m2/s, determine the center and surface temperatures of the apples in 1 h. Also, determine the amount of heat transfer from each apple. Solve this problem using analytical one-term approximation method (notthe Heisler charts). Answer: Center: 11.2 ℃, Surface: 2.7 ℃, heat transfer: 17.2 kJarrow_forwardConsider water (at a temperature of 276 K ) flowing inside a cylindrical pipe, having a diameter of 0.1 m and a thin wall. Under specific circumstances, temperature at the wall of the pipe reaches 258 K that helps form a layer of ice on the inner side of the wall of the pipe. Temperature and convection heat transfer coefficient at the inner surface of the ice layer are 273 K and 1500m2⋅Kw, respectively. Determine how thick the ice layer should be?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_forward
- Water is to be heated from 10°C to 80°C as it flows through a 2-cm-internal-diameter, 7-m-long tube. The tube is equipped with an electric resistance heater, which provides uniform heating throughout the surface of the tube. The outer surface of the heater is well insulated, so that in steady operation all the heat generated in the heater is transferred to the water in the tube. If the system is to provide hot water at a rate of 8 L/min, determine the power rating of the resistance heater. Also, estimate the inner surface temperature of the pipe at the exitarrow_forwardTo warm up some milk for a baby, a mother pours milk into a thin-walled cylindrical container whose diameter is 6 cm. The height of the milk in the container is 7 cm. She then places the container into a large pan filled with hot water at 70°C. The milk is stirred constantly, so that its temperature is uniform at all times. If the heat transfer coefficient between the water and the container is 120 W/m2·K, determine how long it will take for the milk to warm up from 3°C to 38°C. Assume the entire surface area of the cylindrical container (including the top and bottom) is in thermal contact with the hot water. Take the properties of the milk to be the same as those of water. Can the milk in this case be treated as a lumped system? Why?arrow_forwardPulverized coal particles are used in oxy-fuel combustion power plants for electricity generation. Consider a situation where coal particles are suspended in hot air flowing through a heated tube, where the convection heat transfer coefficient is 100 W/m2·K. If the average surface area and volume of the coal particles are 3.1 mm2 and 0.5 mm3, respectively, determine how much time it would take to heat the coal particles to two-thirds of the initial temperature difference.arrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning