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Reply #309: Heat conduction etc. [View All]

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what the Donating Member (11 posts) Send PM | Profile | Ignore Fri Jul-14-06 09:31 PM
Response to Reply #293
309. Heat conduction etc.
Edited on Fri Jul-14-06 09:53 PM by what the
1. Combustion temperature: "It is necessary, when forging puddled iron always to do heavy forging at a high temperature - around 1350 to 1450 degrees Centigrade (bright to sparkling white heat). At these temperatures, the iron will move very quickly, whilst doing no damage to the grain structure. Finishing work, bending etc., can be done at red heat." http://www.realwroughtiron.com/wiac.asp

Edit: No reasonable person is claiming that the steel structure melted. That is not the model for the collapse.

2. The larger the structure, the less heat escapes. The center of a large building can easily be 100 feet away from the outer wall.

3. Regarding conduction of heat by steel beams, I made an estimate with really optimistic assumptions:
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Thermal conductivity of carbon steel: approx. 35 W/(m.deg.C.)
Cross sectional area of steel beam: assume approx. 1 ft.^2, or approx. 0.1 m^2.
Assume that the no heat is lost from the beam to the surrounding structure, which is a very bad assumption, and favors you, not me.

Rate of heat transfer for a 500 deg. C. temperature difference over 30 meter length:

Q = (Area)(Thermal Conductivity)(Temperature Difference)/(Length)

= (0.1 m^2)(35 kW/(m.deg.C)(500 deg.C)/(30 m)

= 59 W.

Over a span of 30 m (about 100 feet) the heat flux is 59 watts. Imagine heating one end of a steel beam with a 60 watt light bulb. In fact it would be less heat flux than that because of heat loss to the surrounding structures in contact with the beam.
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4. "Sherman's neckties" were created by the force of a few soldiers pressing the rail against a tree.

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