A house located in the south of the country was built using windows doubles to reduce heat loss to the outside environment on very cold days. Consider that the house has 6 windows 80 cm high and 1.2 m wide, each consisting of 2 layers of glass (kv=1.4 W/(m.oC) 4 mm thick, separated from each other for a spacing of 10 mm filled with stagnant air (ka=0.024 W/(mK), we disregard natural convection effects) On a day when the interior of the house is kept at 22oC, with h=10 W/(m2. K) while the external environment is at 5oC with h=50 W/(m2.K), it is requested: (a) What is the rate of heat dissipation through the windows? (b) What are the temperatures on the glass surfaces inside and in the exterior of the house? (c) Which of the resistances is the limiting in the dissipation process of heat? (d) Estimate the increase in dissipation rate if we consider that the natural air convection in the space between the windows is characterized by a convective coefficient h=5 W/(m.K). (e) How the value obtained in item (d) could be reduced

A house located in the south of the country was built using windows doubles to reduce heat loss to the outside environment on very cold days. Consider that the house has 6 windows 80 cm high and 1.2 m wide, each consisting of 2 layers of glass (kv=1.4 W/(m.oC) 4 mm thick, separated from each other for a spacing of 10 mm filled with stagnant air (ka=0.024 W/(mK), we disregard natural convection effects) On a day when the interior of the house is kept at 22oC, with h=10 W/(m2. K) while the external environment is at 5oC with h=50 W/(m2.K), it is requested: (a) What is the rate of heat dissipation through the windows? (b) What are the temperatures on the glass surfaces inside and in the exterior of the house? (c) Which of the resistances is the limiting in the dissipation process of heat? (d) Estimate the increase in dissipation rate if we consider that the natural air convection in the space between the windows is characterized by a convective coefficient h=5 W/(m.K). (e) How the value obtained in item (d) could be reduced

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.

Chapter8: Natural Convection

Section: Chapter Questions

Problem 8.7P

See similar textbooks

Similar questions

1.11 Calculate the heat loss through a glass window 7-mm thick if the inner surface temperature is 20°C and the outer surface temperature is 17°C. Comment on the possible effect of radiation on your answer.
1.80 Describe and compare the modes of heat loss through the single-pane and double-pane window assemblies shown in the sketch below. Problem 1.80
A long wire 0.7 mm in diameter with an emissivity of 0.9 is placed in a large quiescent air space at 270 K. If the wire is at 800 K, calculate the net rate of heat loss. Discuss your assumptions.
1.13 If the outer air temperature in Problem is –2°C, calculate the convection heat transfer coefficient between the outer surface of the window and the air, assuming radiation is negligible.
A greenhouse 20m long and 15m wide has a nearly flat roof 3m above the floor level. When the sun is directly overhead the solar flux is 1,000 W/m^2. If the glass roof has an emissivity of 0.9 and the convective losses are 0.8 times the radiation losses, what is the temperature in the greenhouse?
An engineer proposes to decrease the gap between the windows of double pane window to decrease heat transfer. Is it good approach or not? a) Yes, because by this way, less air will be trapped and therefore better insulation b) No, because by this way, radiation heat transfer will increase c) Yes, because by this way, radiation heat transfer will decrease d) No, because by this way, current loops will be created inside the gap e) Not sufficient information
An engineer proposes to decrease the gap between the windows of double pane window to decrease heat transfer. Is it good approach or not? No, because by this way, radiation heat transfer will increase No, because by this way, current loops will be created inside the gap Yes, because by this way, less air will be trapped and therefore better insulation Not sufficient information Yes, because by this way, radiation heat transfer will decrease
A concrete ball of radius 2.32 m and emissivity 0.620 is heated to 123°C. (a) Convert the given temperature to Kelvin. (Enter your answer to at least three significant figures.) ?K (b) What is the surface area (in m2) of the ball? ?m2 (c) If the ambient temperature is 26.0°C, what net power (in W) does the ball radiate? ?W
An astronaut performing an extra-vehicular activity(space walk) shaded from the Sun is wearing a spacesuitthat can be approximated as perfectly white (e = 0) exceptfor a 5 cm × 8 cm patch in the form of the astronaut’snational flag. The patch has emissivity 0.300. The spacesuitunder the patch is 0.500 cm thick, with a thermalconductivity k = 0.0600 W/m °C , and its inner surface isat a temperature of 20.0 °C . What is the temperature of thepatch, and what is the rate of heat loss through it? Assumethe patch is so thin that its outer surface is at the sametemperature as the outer surface of the spacesuit under it.Also assume the temperature of outer space is 0 K. You willget an equation that is very hard to solve in closed form,so you can solve it numerically with a graphing calculator,with software, or even by trial and error with a calculator.
A 4-mm-diameter sphere at 50°C is covered by a 1-mm-thick plastic insulation (k=0.13 W/m°C). The sphere is exposed to a medium at 15 °C, with a combined convective and radiative heat transfer coefficient of 20 W/m2 °C. Determine whether the plastic insulation over the sphere will help or harm heat transfer from the sphere.
The emissivity of galvanized steel sheet, a common roofing material, is ε = 0.13 at temperatures around 300 K, while its absorptivity for solar irradiation is αS = 0.65. Would the neighborhood cat be comfortable walking on a roof constructed of the material on a day when GS = 750 W/m2, T∞ = 16°C, and h = 7 W/m2 · K? Assume the bottom surface of the steel is insulated.
The solar power striking Earth every day averages 168watts per square meter. The highest ever recorded electricalpower usage in New York City was 13,200 MW. A recordestablished in July of 2013. Considering that present technologyfor solar energy conversion is about 10% efficient,from how many square meters of land must sunlight becollected in order to provide this peak power? (For comparison,the total area of New York City is 830 km2.)