Introduction to Heat Transfer
6th Edition
ISBN: 9780470501962
Author: Frank P. Incropera, David P. DeWitt, Theodore L. Bergman, Adrienne S. Lavine
Publisher: Wiley, John & Sons, Incorporated
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Chapter 3, Problem 3.31P
A commercial grade cubical freezer, 3 m on a side,has a composite wall consisting of an exterior sheetof 6.35-mm-thick plain carbon steel, an intermediatelayer of 100-mm-thick cork insulation, and an innersheet of 6.35-mm-thick aluminum alloy (2024).Adhesive interfaces between the insulation and themetallic strips are each characterized by a thermal contactresistance of
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A cold storage room has a wall consists of an inside finish of 0.60 in cement plaster(k = 0.67), two layers of corkboard each 2.5 in thick (k = 0.03) and an outside layer of building tile. The value of U for the entire wall is 0.058, the internal air filmcoefficient is 1.65, the inner temperature is 23°F and the outside temperature is85°F. Calculate the heat flow through the unit wall area, Btu/hr.ft2A. 1.47 B. 2.47 C. 3.47 D. 4.47
c) A steel pipe of 100 mm bore, and 10 mm bore thickness, carrying dry saturated steam at 28
bars, is insulated with a 40 mm layer of moulded insulation. This insulation in turn is
insulated with a 60 mm layer of felt. The atmospheric temperature is 15 °C.
Calculate:
(i) the rate of heat loss by the steam per metre pipe length.
(ii) the temperature of the outside
Dimensions in mm
surface.zzzzzzz
h₂-15 W/m²K
Steel
k₁=50 W/mK
AVALEHT
Ø100
1₂
"
Steam 28 bar
h-550 W/m²K,
Inner heat transfer coefficient = 550 W/m² K
Outer heat transfer coefficient = 15 W/m² K
Thermal conductivity of steel = 50 W/m K
Thermal conductivity of felt = 0.07 W/m K
Moulded
insulation
Felt
Moulded insulation
K₂=0.09 W/mK
Thermal conductivity of moulded insulation = 0.09 W/m
40
10.
A
60
15°C
Felt
K₁=0.07 W/mK
zzzzzzzz
Two inches of urethane foam will reduce heat loss close to 1000% when applied to a 2-inch diameter uninsulated steel pipe. Assume the pipe wall thickness is 0.25-inches, the pipe interior convective heat loss (hi) is 500 BTU/hr-ft2-oF, and the pipe outside convective heat loss ho 20 BTU/hr-ft2-oF, k steel is 25 BTU/hr-ft-oF, and k insulaton is 0.023 BTU/hr-ft-oF. (hint - calculate heat loss with and without insulation.
Chapter 3 Solutions
Introduction to Heat Transfer
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