On Fri, Jul 22, 2011 at 1:06 AM, Joshua Cude <joshua.c...@gmail.com> wrote:
> I don't get that. If it takes one unit of power to bring the temperature up > to the ignition threshold, and then the thing generates 6 or more units of > power on its own, I can't see how removing the first one could possibly > bring the temperature below ignition. > > I don't either. Do have a sound argument that says it can't happen? I don't. I'm looking for it. A good of an uncontrollable exothermic reaction is the ignition of gun powder. Taking away the match will not stop the reaction. A counter example is the evolution of tunsten vapor from a heated light bulb fiaiment. If, somewhere in the filament is a length that is two or three percent smaller in diameter than the rest, the filament will eventually burn through at this spot. The narrow section runs a little hotter. Because it runs a little hotter, the tungsten in this section vaporizes a little faster than the rest of the filament. This causes it's resistance to decrease faster than the rest of the wire. This in turn causes it to vaporize faster, so there is positive feedback. Eventually the tiny difference in diameter will cause the filament to fail at this point. And this is how most light bulbs eventually fail. But it's easy to control. We just turn off the light switch and we've turned off the run-away reaction. In the same way a heat source that stimulates an small exothermic reaction can be controlled if it requires a large source of heat. So................How is this quantified, and does it disclude the claims made of Rossi's gadget as non physical? > To me, if the thing that initiates the reaction is heat, and the reaction > generates even more heat, it will sustain itself, just like combustion. You > need matches to start fires, but not to sustain them. > > Yes, another good example of an uncontrollable exothermic reaction.
