example 5-2 - Example 5-2 A steam pipe with an OD of 6 in....

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Example 5-2 A steam pipe with an OD of 6 in. is at a temperature of 700°F. Two layers of insulation cover the pipe, as shown. The layer closest to the pipe can withstand high temperatures and has a thermal conductivity of 0.122 Btu/h·ft·°F. A less expensive type of insulation with a thermal conductivity of 0.0215 Btu/h·ft·°F is used for the second layer. This second layer can only withstand temperatures of 550°F or less. Air cools the exterior of the insulation with a heat transfer coefficient of 4.2 Btu/h·ft 2 ·°F. Using geometry data on the figure, a) Find the surface temperature, T 3 b) Determine whether the low temperature insulation fails under these conditions
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Solution: The relevant radii are 1 3in. 0.25ft in. 12 ft r == 21 2in 0.417ft in 12 ft rr =+ = 32 3in 0.667ft in 12 ft = The thermal resistances are o 2 1 1 1 o hf t F ln ln 0.666 0.25ft Btu Btu 2 2 0.122 r r R kL L L π ⎛⎞ ⎜⎟ ⎝⎠ = ⋅⋅ o 3 2 2 2 o 0.667ft ln ln 3.48 Btu Btu 2 20 . 0 2 1 5 r r R L L =
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() o 3 3 2o hf t F 0.0568 11 1 Btu Btu 2 4.2 2 0.667ft t F R hA h r L L L π == = = ⎛⎞ ⎜⎟
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This note was uploaded on 04/06/2009 for the course ENGR 2250 taught by Professor Borca-tasciuc during the Spring '08 term at Rensselaer Polytechnic Institute.

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example 5-2 - Example 5-2 A steam pipe with an OD of 6 in....

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