----- Original Message ----- From: "Gautam Mukunda" <[EMAIL PROTECTED]> To: "Killer Bs Discussion" <[EMAIL PROTECTED]> Sent: Thursday, October 16, 2003 10:48 AM Subject: Re: fire paste
> --- The Fool <[EMAIL PROTECTED]> wrote: > > > <<http://www.baytoday.ca/content/news/details.asp?c=63>> > > > > Inventor spurns burns with red-hot invention > > 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. > It's the difference between sticking your hand in an > oven at 400 degrees (safe, because the air will not > transfer heat to your hand fast enough to burn it) and > touching the metal _in_ the oven (not safe). Radiative heating works in a vacume. Photons are emitted by the source and are absorbed by the sink. So, radiative heating in an oven has nothing to do with whether you touch the hot item. That is conductive heating. Very rarely is radiative heating a better way of transfering energy than conductive heating. The only example I can think of where this could be said is with a laser...a laser beam can be hot enough to weld metal without destroying the housing of the laser. Think about holding your hands close to a very hot flame with a lot of heat associated with it; say a blow torch. Now, if you hold your hands above them, convection may cause significant heating. But, if you hold your hands beneith them, with a highly transparent material with low thermal conductivity between them, your hands will be warmed, but not overwhelmingly. Compare that to what would happen if you actually contacted the blow torch. As Erik stated, the low thermal conductivity of shuttle tiles is the main reason they are effective. Indeed, the shuttle tiles that are subjected to the greatest heat are black, so they can better emit photons to cool themselves. Finally, considering the fire paste, I have a hard time believing that a spray on paste that washes off with water will stand up to supersonic turbulant airflow without erosion. Dan M. > _temperature_ of the two substances is the same, it's > the energy transfer that's different. Isn't that all > that's happening here? > > ===== > Gautam Mukunda > [EMAIL PROTECTED] > "Freedom is not free" > http://www.mukunda.blogspot.com > > __________________________________ > Do you Yahoo!? > The New Yahoo! Shopping - with improved product search > http://shopping.yahoo.com > _______________________________________________ > http://www.mccmedia.com/mailman/listinfo/brin-l > _______________________________________________ http://www.mccmedia.com/mailman/listinfo/brin-l
