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A section of a composite wall with the dimensions shown below has uniform temperatures of 200°C and 50°C over the left and right surfaces, respectively. If the thermal conductivities of the wall materials are:
Repeat Problem 1.34, including a contact resistance of 0.1 K/W at each of the interfaces.
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Chapter 1 Solutions
Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)
- 1.4 To measure thermal conductivity, two similar 1-cm-thick specimens are placed in the apparatus shown in the accompanying sketch. Electric current is supplied to the guard heater, and a wattmeter shows that the power dissipation is 10 W. Thermocouples attached to the warmer and to the cooler surfaces show temperatures of 322 and 300 K, respectively. Calculate the thermal conductivity of the material at the mean temperature in W/m K. Problem 1.4arrow_forward1.10 A heat flux meter at the outer (cold) wall of a concrete building indicates that the heat loss through a wall of 10-cm thickness is . If a thermocouple at the inner surface of the wall indicates a temperature of 22°C while another at the outer surface shows 6°C, calculate the thermal conductivity of the concrete and compare your result with the value in Appendix 2, Table 11.arrow_forwardA section of a composite wall with the dimensions shown below has uniform temperatures of 200C and 50C over the left and right surfaces, respectively. If the thermal conductivities of the wall materials are: kA=70W/mK,kB=60W/mK, kC=40W/mK, and kD=20W/mK, determine the rate of heat transfer through this section of the wall and the temperatures at the interfaces.arrow_forward
- 2.51 Determine by means of a flux plot the temperatures and heat flow per unit depth in the ribbed insulation shown in the accompanying sketch.arrow_forward1.37 Mild steel nails were driven through a solid wood wall consisting of two layers, each 2.5-cm thick, for reinforcement. If the total cross-sectional area of the nails is 0.5% of the wall area, determine the unit thermal conductance of the composite wall and the percent of the total heat flow that passes through the nails when the temperature difference across the wall is 25°C. Neglect contact resistance between the wood layers.arrow_forward2.38 The addition of aluminum fins has been suggested to increase the rate of heat dissipation from one side of an electronic device 1 m wide and 1 m tall. The fins are to be rectangular in cross section, 2.5 cm long and 0.25 cm thick, as shown in the figure. There are to be 100 fins per meter. The convection heat transfer coefficient, both for the wall and the fins, is estimated to be K. With this information determine the percent increase in the rate of heat transfer of the finned wall compared to the bare wall.arrow_forward
- The wall of a furnace is made up of a material which has thermal conductivity of 2.65 W/m◦C and a thicknesses 300 mm. The inner side of the furnace wall is exposed to hot gases at 1200 ⁰C with a convection coefficient of 20 W/m2⁰C and the inside the surface is at 700 ⁰C. The air outside the furnace is at 20⁰C with a convection coefficient of 15 W/m2⁰C. Draw a clear diagram representing the system Determine the temperature of the outside surface of the furnace The rate of heat loss from the furnace.arrow_forward16. A steel pipe 1.5-m in length has an inside diameter of 7.6 cm with a wall thickness of 11.6 mm. The steel has a thermal conductivity of 46 W/m K. The pipe is covered with a 4 cm thick layer of insulation with a thermal conductivity of 0.4 W/m K. What is the total thermal resistance from the inside surface of the pipe to the outside surface of the insulation layer? Express your answer in °C/W or K/W.arrow_forwardThe heat loss per hour through 1 sq. ft of furnace wall 18" thick is 520 Btu. The temperature on the hot side of the wall is 1900 degrees F, and its average thermal conductivity is 0.61 Btu/hr-ft-°F. Determine the temperature on the other side of the wall in °C.arrow_forward
- A hot steam pipe having an inside surface temperature of 250°C has an inside diameter of 8 cm and a wall thickness of 5.5 mm. It is covered with a 9-cm layer of insulation having k =0.5 W/m-°C, followed by a 4-cm layer of insulation having k =0.25W/m-°C. The outside temperature of the insulation is 20°C. Calculate the heat lost per meter of length. Assume k =47 W/m-°C for the pipe.arrow_forwardA cold storage room is constructed of an inner layer of 12.7 mm of pine, a middle layer of 101.6 mm of cork board, and an outer layer of 76.2 mm of concrete. The wall surface temperature is 255.4 K inside the cold room and 297.1 K at the outside surface of the concrete. The conductivities for pine, for cork board and for concrete are 0.151 W/m.K, 0.0433 W/m.K, 0.762 W/m.K respectively. Calculate the heat loss in W for 1 m2 and the temperature at the interface between the wood and cork board.arrow_forwardThe section of a vertical wall is made up of fiberglass insulation slabs separated by wooden studs. The thermal conductivity of fiberglass and wood are 0.04 W/m∙K and 0.18 W/m∙K, respectively. The thickness of the wall is 180 mm. The temperatures of the inner and outer surfaces of the wall section are 23.5 °C and 4.7 °C, respectively. The ratio of the insulation area to the total wall area is 0.8. Calculate the total heat flow rate (in W/m2) through the wall per unit area.arrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning