On Thu, Oct 16, 2003 at 08:48:14AM -0700, Gautam Mukunda wrote: > My physics is far enough in the past that I'm probably going to screw > this up (I'm sure Dan is going to correct me) but this doesn't seem > all that remarkable, and I think he's completely misunderstanding > what's happening. You can heat (for example) the thermal protective > tiles on the shuttle to thousands of degrees and then touch them with > your bare hand, as I recall, because they absorb the heat and then > _fail_ to radiate it, not because they cool immediately.
No, they DO radiate (and convect) the heat away. Those tiles are special due to their extremely low thermal conductivity. There is a famous picture of a person holding a cube of this material. The center of the cube is glowing red hot (indicating it is radiating heat), but the edges are cool enough to touch since the heat at the center has not been able to conduct to the edges faster than the edges can cool in the air. > energy transfer that's different. Isn't that all that's happening > here? The description is really sketchy, so I am not sure what is happening. Did the "fire foam" get hot from the torch? The best fire protector I can think of would have very high thermal mass (i.e., it takes a lot of energy to raise its temperature) and very low thermal conductivity. So the outside could absorb a lot of heat without getting too hot, and the middle would not conduct much heat to the inside. Obviously the material would also need to be non-flammable and be able to withstand high temperatures without breaking down. I think you are right that the shuttle's thermal tiles meet these criteria (although I'm not sure how high their thermal mass is). But I think they are quite brittle, right? He said this stuff is a foam, presumably you can spray it on. That would be a huge improvement over all the trouble of the shuttle tiles. -- Erik Reuter http://www.erikreuter.net/ _______________________________________________ http://www.mccmedia.com/mailman/listinfo/brin-l
