13.38 Consider the attic of a home located in a hot climate.The floor of the attic is characterized by a width ofL₁ = 8 m while the roof makes an angle of 0 = 30° fromthe horizontal direction, as shown in the schematic.The homeowner wishes to reduce the heat load to thehome by adhering bright aluminum foil (ε = 0.07) ontothe surfaces of the attic space. Prior to installation ofthe foil, the surfaces are of emissivity & = 0.90.AtticA2, 82, T2 0 = 30°A1, E1, T₁土L₁ = 8 m(a) Consider installation on the bottom of the atticroof only. Determine the ratio of the radiation heattransfer after to before the installation of the foil.(b) Determine the ratio of the radiation heat transferafter to before installation if the foil is installedonly on the top of the attic floor.(c) Determine the ratio of the radiation heat transfer ifthe foil is installed on both the roof bottom and thefloor top.

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Answered: 13.38 Consider the attic of a home…

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 8.26P

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Using Table 1.4 as a guide, prepare a similar table showing the orders of magnitude of the thermal resistances of a unit area for convection between a surface and various fluids.
1.2 The weight of the insulation in a spacecraft may be more important than the space required. Show analytically that the lightest insulation for a plane wall with a specified thermal resistance is the insulation that has the smallest product of density times thermal conductivity.
Draw the thermal circuit for heat transfer through a double-glazed or a double-paned window. Identify each of the circuit elements. Include solar radiation to the window and interior space.
1.3 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.
Repeat Problem 1.35 but assume that instead of surface temperatures, the given temperatures are those of the air on the left and right sides of the wall and that the convection heat transfer coefficients on the left and right surfaces are 6 and 10W/m2K, respectively.
A one-story house is built over a vented crawl space. The attic is alsovented. The heating system is designed for a temperature difference of 75°F.The exterior wall of a middle bedroom is shown. The room is 10 feet 3 incheswide. The window has double pane glass. The wall is wood frame withsheathing and siding. It has 1 inch of polystyrene insulation over 31⁄2 inchesof insulation (total R-16). The ceiling has 91⁄2 inches of insulation (R-30),and the floor has 6 inches of insulation (R-19). Find the heat load for thisroom.
The diagram below illustrates a simplified version of the Jet Propulsion Laboratory's 25-ft space simulator chamber. Within it, tests are run for deep space probes and their components. In this particular experiment, a sensor assembly with its housing is placed inside. The sensor-housing electronics create heat such that q=3181.0 W exits the assembly's top surface into the chamber. The chamber itself is under vacuum, and its walls are at cryogenic temperatures to simulate conditions in space. Surfaces 1 and 2 are flat. Assume they are flush. The top surface of the chamber, Surface 4, can be approximated as a perfectly insulated, flat ceiling. The exposed surface of the floor, Surface 2, is a black, donut- shaped surface. Additional surface information can be seen below, including various parameters and dimensions. Assume all surfaces are opaque and diffuse, and conditions are at steady-state. PARAMETERS & DIMENSIONS Surface 1: A = 7.07 m²; diameter d; = 3 m; &₁ = 0.5; Surface 2: A₂ =…
An electronic device with a temperature of 84°C (shown in golden colour) is embedded inside a composite plastic tube which is equipped with three fins (shown in blue) to enhance the convective heat transfer with the surrounding air. The composite tube is held horizontally. The temperature drop along the fins can be ignored due to their high thermal conductivity. The outer ring of the fins (shown in brown) is insulated. The ambient temperature is 20°C. 3a. Draw the thermal resistance circuit of the system 3b. Derive the energy balance of the system 3c. Find the thermos-physical properties of the air and aluminium 3d. Calculate the heat transfer coefficients across the cylinder 3e. Calculate the heat transfer coefficients across the fins by assuming fins as vertical planes 3f. Calculate the heat loss across the system
A wall in a house contains a single window. The window consists of a single pane of glass whose area is 0.13 m2 and whose thickness is 8 mm. Treat the wall as a slab of the insulating material Styrofoam whose area and thickness are 19 m2 and 0.10 m, respectively. Heat is lost via conduction through the wall and the window. The temperature difference between the inside and outside is the same for the wall and the window. Of the total heat lost by the wall and the window, what is the percentage lost by the window?
Problem 5.18: A furnace has inside dimensions of 1 m × 1.2 m × 1.5 m. The walls are 0.25 m thick. The inside surface is at 750°C while the outside surface is at 80°C. If the conductivity of the material is 0.45 W/mK determine the heat loss, taking into account the corner and edge effects and also the bottom. (shape factors are taken from hand books). h-1
Question 3: An electronic device with a temperature of 84°C (shown in golden colour) is embedded inside a composite plastic tube which is equipped with three fins (shown in blue) to enhance the convective heat transfer with the surrounding air. The composite tube is held horizontally. The temperature drop along the fins can be ignored due to their high thermal conductivity. The outer ring of the fins (shown in brown) is insulated. The ambient temperature is 20°C. 3a. Draw the thermal resistance circuit of the system 3b. Derive the energy balance of the system 3c. Find the thermo-physical properties of the air and aluminium Aluminium fins Diameter = 30 cm Insulated ring Thickness = 5 mm Composite tube Thickness = 5 mm Thermal conductivity 25 W/mK Tube is held horizontally. Air 20°C Hot electronic device Temperature = 84°C Diameter = 10 cm Length = 100 cm
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