Sustainable Energy
2nd Edition
ISBN: 9781337551663
Author: DUNLAP, Richard A.
Publisher: Cengage,
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3.
6.0" wide wooden fence posts are embedded in a concrete driveway a distance 12.125" apart. There is
a 1/16" gap between the post and the concrete (see diagram). The posts are installed when the temperature is
12°C. Determine if the gap will close when the temperature increases to 32°C and if not how big the gap will
be at that temperature. The thermal expansion coefficients of wood and concrete are awood =32 x 105 °C and
aconcrete =13 x 106 °C. 1 inch3D2.54 cm.
6.0"
12.0"
0.0625"
A 1,065 ft², 7 in. thick concrete wall has inside and outside surface temperatures of 25°C and 9°C. A 2 in. insulation batt with a thermal conductivity of k = 0.03 Btu/(h· ft· °F) is added
to the wall. Determine the reduction in heat transfer rate.
What is the thickness of the insulation in meters?
m
What is the thermal conductivity value of the insulation batt in W/(m .K)?
W/(mK)
What is the R-value of the concrete wall (in m². K/W)?
m². K/W
What is the R-value of the insulation batt (in m². K/W)?
m². K/W
What is the heat transfer rate (in W) when the insulation is added?
W
What is the percent reduction in the heat transfer rate?
%
Question 11
Which statement about thermal conductivity is FALSE?
O a. The thermal conductivity of timber is greater in the longitudinal compared to the radial direction.
O b. Lower density results in lower thermal conductivity.
C. Thermal modification of wood reduces its thermal conductivity.
Od. Thermal conductivity of air is higher compared to wood.
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- calculate the heat loss through the ceiling, if the R-19 insulation batt is replaced by R-40 fiberglass insulation.arrow_forwardParker County Community College (PCCC) is trying to determine whether to use no insulation or to use insulation that is either 1 inch thick or 2 inches thick on its steam pipes. The heat loss from the pipes without insulation is expected to cost $1.50 per year per foot of pipe. A 1-inch thick insulated covering will eliminate 89% of the loss and will cost $0.40 per foot. A 2-inch thick insulated covering will eliminate 92% of the loss and will cost $0.85 per foot. PCCC Physical Plant Services estimates that there are 250,000 feet of steam pipe on campus. The PCCC Accounting Office requires a 10%/year return to justify capital expenditures. The insulation has a life expectancy of 10 years. Determine which insulation (if any) should be purchased using a ranking future worth analysis.arrow_forward80° -Sheathing 70° Gypsum wallboard 60° Fiberglass between studs Siding 50° Air inside room 40° at 72F Air outside at 0F 30° 20° 10° 0 1 2 3 4 5 6 7 Distance through wall (inches) The temperature changes in the wall - Insulation According to the figure materials is the best insulator? The poorest? Explain. which of the Temperature (°F)arrow_forward
- A line measured with a 50-m long steel tape was determined to be 645.22 meter when the average temperature during taping was 15.750C. If the tape is of standard length at 200C and the coefficient of thermal expansion of steel is 0.0000116/10C, the correct length of the measured line isarrow_forwardQ2/ How much heat does 50g of aluminum give off as it cools from 100c° to 10c°? for aluminum c=88 J/Kg.c°.arrow_forwardQ1: A. 6 kg of steel, specific heat capacity 500 J\Kg K, is heated from 59°F to 212°F C. How much heat is required?arrow_forward
- Urgent..... Classify the following materials with regard to their thermal insulation properties, rate them from the best to the worst: Solid concrete block, Burned clay block, clay brick. Cement - sand bricks, light weight blocks, and hollow concrete blocks.arrow_forward12. Thermal efficiency using temperature values 13. Thermal efficiency using rc and k valuesarrow_forward3-Typical asphalt roofing shingles have a thermal conductivity of about 0.79 W/m-k. If the temperature inside the house is 75 F and the temperature outside is 5 F, find the heat flux (the rate of heat transfer divided by the surface area through which conduction occurs ) through a 2 cm thick asphalt shingle roof.arrow_forward
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