The exterior wall of a house is composed of a 20 cm thick layer of ordinary brick (conductivity 0.72 W/m K) and a 2.5 cm layer of plaster (conductivity 0.17 W/m K ) on each side (two layers in total). Other purely conductive resistances can be neglected, such as the layer of paint on both sides of the wall. Assume the outer face of the wall is at 35 °C and the inner face is at 20 °C and fill in the gaps. The magnitude of the heat flux through the wall corresponds to the _________ W/m2 and is perpendicular to the wall ________________ (fill in with "outside-in" or "inside-out") of the environment. If the wall has a total area of 300m2, the heat transfer rate corresponds to ___________________

The exterior wall of a house is composed of a 20 cm thick layer of ordinary brick (conductivity 0.72 W/m K) and a 2.5 cm layer of plaster (conductivity 0.17 W/m K ) on each side (two layers in total). Other purely conductive resistances can be neglected, such as the layer of paint on both sides of the wall. Assume the outer face of the wall is at 35 °C and the inner face is at 20 °C and fill in the gaps. The magnitude of the heat flux through the wall corresponds to the _ W/m2 and is perpendicular to the wall (fill in with "outside-in" or "inside-out") of the environment. If the wall has a total area of 300m2, the heat transfer rate corresponds to ___________

Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)

8th Edition

ISBN:9781305387102

Author:Kreith, Frank; Manglik, Raj M.

Publisher:Kreith, Frank; Manglik, Raj M.

Chapter1: Basic Modes Of Heat Transfer

Section: Chapter Questions

Problem 1.37P: 1.37 Mild steel nails were driven through a solid wood wall consisting of two layers, each 2.5-cm...

See similar textbooks

Similar questions

1.10 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.
1.1 On a cold winter day, the outer surface of a 0.2-m-thick concrete wall of a warehouse is exposed to temperature of –5°C, while the inner surface is kept at 20°C. The thermal conductivity of the concrete is 1.2 W/m K. Determine the heat loss through the wall, which is 10-m long and 3-m high. Problem 1.1
3.16 A large, 2.54-cm.-thick copper plate is placed between two air streams. The heat transfer coefficient on one side is and on the other side is . If the temperature of both streams is suddenly changed from 38°C to 93°C, determine how long it takes for the copper plate to reach a temperature of 82°C.
1.37 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.
2.9 In a large chemical factory, hot gases at 2273 K are cooled by a liquid at 373 K with gas-side and liquid-side convection heat transfer coefficients of 50 and , respectively. The wall that separates the gas and liquid streams is composed of a 2-cm thick oxide layer on the gas side and a 4-cm thick slab of stainless steel on the liquid side. There is a contact resistance between the oxide layer and the steel of . Determine the rate of heat loss from hot gases through the composite wall to the liquid.
An electronic device that internally generates 600 mW of heat has a maximum permissible operating temperature of 70C. It is to be cooled in 25C air by attaching aluminum fins with a total surface area of 12cm2. The convection heat transfer coefficient between the fins and the air is 20W/m2K. Estimate the operating temperature when the fins are attached in such a way that (a) there is a contact resistance of approximately 50 K/W between the surface of the device and the fin array and (b) there is no contact resistance (in this case, the construction of the device is more expensive). Comment on the design options.
A high-speed computer is located in a temperature-controlled room at 26C. When the machine is operating, its internal heat generation rate is estimated to be 800 W. The external surface temperature of the computer is to be maintained below 85C. The heat transfer coefficient for the surface of the computer is estimated to be 10W/m2K. What surface area would be necessary to assure safe operation of this machine? Comment on ways to reduce this area.
The wall of a furnace consists of 200 mm thick refractory brick (k = 3 Btu / hr-ft2-0F), 100 mm thick bricks (k = 0.050 Btu / hr-ft2-0F) and 6 mm thick steel. The temperature on the side of the refractory brick layer of the furnace is 1150 C, and the temperature on the outer steel surface is 30C. There is a heat loss of 300 W / square meter at the wall of the furnace. It is difficult to prevent the thin air additions between the brick layers and the brick layer and the steel wall. How many mm of brick layers is the total thickness of these air layers equivalent?
A thick-walled tube of stainless steel with thermal conductivity k=19 W/m°C has inner diameter of 10 cm and outer diameter of 30 cm covered with 5 cm layer of asbestos insulation with thermal conductivity k= 0.2 W/m°C. If the inside of the pipe and outside of insulator temperature is maintained at 600°C and 107°C respectively. Determine the heat loss per meter length of pipe and the tube-insulation interface temperature.
‏Q1 / A5 - cm - diameter steel pipe is covered with a 1 - cm layer of insulating material having k = 0.22 W / m . ° C followed by a 3 - cm - thick layer of another insulating material having k = 0.06 W / m . ° C . The system is exposed to a convection surrounding condition of h = 60 W / m² . ° C and T -15 ° C . The outside surface temperature of the steel pipe is 400 ° C . Calculate the heat lost by the pipe - insulation assembly for a pipe length of 20 m . Express in Watts .
A two-layer wall is made of two metal plates, with surface roughness of about 25 mm, pressed together at an average pressure of 10 MPa. The first layer is a stainless steel plate with a thickness of 5 mm and a thermal conductivity of 14 W/m∙K. The second layer is an aluminum plate with a thickness of 15 mm and a thermal conductivity of 237 W/m∙K. On the stainless steel side of the wall, the surface is subjected to a heat flux of 800 W/m2. On the aluminum side of the wall, the surface experiences convection heat transfer at an ambient temperature of 20°C, where the convection coefficient is 12 W/m2∙K. Determine the surface temperature of the stainless steel plate.
16. 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.