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Chapter 1 Solutions
Introduction to Heat Transfer
- As a designer working for a major electric appliance manufacturer, you are required to estimate the amount of fiberglass insulation packing (k = 0.035 W/m K) that is needed for a kitchen oven shown in the figure below. The fiberglass layer is to be sandwiched between a 2-mm-thick aluminum cladding plate on the outside and a 5-mm-thick stainless steel plate on the inside that forms the core of the oven. The insulation thickness is such that the outside cladding temperature does not exceed 40C when the temperature at the inside surface of the oven is 300C. Also, the air temperature in the kitchen varies from 15Cto33C, and the average heat transfer coefficient between the outer surface of the oven and air is estimated to be 12.0W/m2K. Determine the thickness of the fiberglass insulation that is required for these conditions. What would be the outer surface temperature when the inside surface of the oven is at 475C?arrow_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_forward1.3 A furnace wall is to be constructed of brick having standard dimensions of Two kinds of material are available. One has a maximum usable temperature of 1040°C and a thermal conductivity of 1.7 W/(m K), and the other has a maximum temperature limit of 870°C and a thermal conductivity of 0.85 W/(m K). The bricks have the same cost and are laid in any manner, but we wish to design the most economical wall for a furnace with a temperature of 1040°C on the hot side and 200°C on the cold side. If the maximum amount of heat transfer permissible is 950 , determine the most economical arrangement using the available bricks.arrow_forward
- 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_forward1.37 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_forwardA steel pipe (outside diameter 100 mm) is covered with two layers of insulation. The inside layer, 40 mm thick, has a thermal conductivity of 0.07 W/(m K). The outside layer, 20 mm thick, has a thermal conductivity of 0.15 W/(m K). The pipe is used to convey steam at a pressure of 600 kPa. The outside temperature of insulation is 24°C. If the pipe is 10 m long, determine the following, assuming the resistance to conductive heat transfer in steel pipe and convective resistance on the steam side are negligible: a. The heat loss per hour. b. The interface temperature of insulation.arrow_forward
- An electric furmace is a composite wall consisting of a brick with 0.2 m refractory brick (k=2), 0.15 m insulation (k =0.15) and 0.15 m (k= 1.5) references The internal and external temperatures of the wall are 1027 °C and 27 °C, respectively. k units are kcal-m/H m2 °C. If the surface area of the wall is 1.2 m2 calculate the heat transfer rate accordingly (kcal/h). Please select one: a.10000 b.1000 c.10 d.100 e. None of themarrow_forwardHomework O H.W. 1: The walls of a refrigerator are typically constructed by sandwiching a layer of insulation between sheet metal panels. Consider a wall made from fiberglass insulation of thermal conductivity k; = 0.046 W/m.K and thickness L, = 50 mm and steel panels, each of thermal conductivity k, = 60 W/m.K and thickness L, = 3 mm. If the wall separates refrigerated air at T = 4 C from ambient air at T,. = 25 C, what is the heat gain per unit surface area? Coefficients associated with natural convection at the inner and outer surfaces may be approximated as h, = h, = 5 W/m?.K. %3D %3D L; = 0.050 m K K Lo = 0.003 m Refrigerated air Ambient air Too.i = 4°C hi = 5 W/m2-K To,o = 25°C ho = 5 W/m2-K %3D Panel (2) kp = 60 W/m-K Insulation k; = 0.046 W/m-K 22 Warith Alanbiyaa (Dr. ALI M) Heat Transfer Page 11 ofarrow_forwardSteel pipe (outer diameter 100 mm) is covered with two layers of insulation. The inner layer, 40 mm thick, has a thermal conductivity of 0.07 W / (m K). The outer layer, 20 mm thick, has a thermal conductivity of 0.15 W / (m K). Pipes are used to deliver steam with a pressure of 500 kPa. The temperature on the outer insulation surface is 24 ° C. If the pipe is 8 m long, determine the following: (assuming that the conduction heat transfer resistance of the steel pipe and the vapor convection resistance are negligible). a. Heat loss per hour. = Answer kJ / hour. b. Temperature between insulation layers. = Answer ° C.arrow_forward
- Steel pipe (outer diameter 100 mm) is covered with two layers of insulation. The inner layer, 40 mm thick, has a thermal conductivity of 0.07 W / (m K). The outer layer, 20 mm thick, has a thermal conductivity of 0.15 W / (m K). Pipes are used to deliver steam with a pressure of 600 kPa. The temperature on the outer insulation surface is 24 ° C. If the pipe is 8 m long, determine the following: (assuming that the conduction heat transfer resistance of the steel pipe and the vapor convection resistance are negligible). a. Heat loss per hour. = kJ / hour. b. Temperature between insulation layers. = ° Carrow_forwardSteel pipe (outer diameter 100 mm) is covered with two layers of insulation. The inner layer, 40 mm thick, has a thermal conductivity of 0.07 W / (m K). The outer layer, 20 mm thick, has a thermal conductivity of 0.15 W / (m K). Pipes are used to deliver steam with a pressure of 800 kPa. The temperature on the outer insulation surface is 24 ° C. If the pipe is 10 m long, determine the following: (assuming that the conduction heat transfer resistance of the steel pipe and the vapor convection resistance are negligible). a. Heat loss per hour. = AnswerkJ / hr. b. Temperature between insulation layers. = Answer ° C.arrow_forwardTwo walls of cold storage plant are composed of an insulating material (k = 0.25 kJ/hr-m-°C), 100mm thick at the outer layer and material (k = 3.5 kJ/hr-m-°C), 15mm thick at inner layer. If the surface temperature at the cold side is 30 °C and hot side is 250 °C, find the heat transmitted per square meter.arrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning
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