If incandescent lightbulbs have a vacuum inside, why do they get so hot on the outside?
If incandescent lightbulbs have a vacuum inside, why do they get so hot on the outside?
Shouldn't the vacuum insulate the glass from the heat of the burning filament?
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Maybe they are thinking of how mugs and thermoses can be labeled “vacuum sealed,” and that the marketing implies that the vacuum between the walls insulates the outer wall (where the hand touches) against the heat.
And those are usually made out of some metal, that'll do pretty good reflecting radiation heat transfer
for better insulation you can put more reflecting layers inside. i've heard of insulation for liquid helium pipe, it used thousands of layers of aluminized mylar between two tubes in vacuum. it's one barrier between 4.2K and room temperature, and it works good enough to be used in helium manufacturing plant
You ever seen those vacuum ovens too? Kinda doing the opposite, only letting radiation in, but from just solar radiation I've heard in sub zero temps they can get to a constant 500 F. Wonder what one would be capable of with some one way mirror type refraction to keep all that shit in
yes but no reflective surfaces involved this time, at least not for insulation. compare that to vacuum tube water heater, it has a heat pipe with a fin, painted black, which is in turn insulated with a two walled evacuated glass tube. it's there just to stop convection from carrying heat away. i guess something very similar is going on there
It does do that though. My vacuum thermos keeps things hot or cold for like 6 hours