Temperature in Vacuum Insulation
Most recent answer: 03/30/2015
- c p bhagyanath (age 23)
punjab,india
That's a nice question. Let me answer on the assumption that the walls are perfect absorbers-emitters, just for simplicity. In a real thermos bottle or dewar they would actually be silvered to make them very poor absorber-emitters.
It turns out that the intermediate space doesn't have a definite temperature. Any definite temperature implies a particular spectrum of how much radiation energy there is in each frequency range. In this case the radiation spectrum is a mix of 77K and 300K spectra. If you were to pick a temperature based on the radiation at one frequency you'd get a different temperature than what you'd calculate based on the radiation at another frequency. The average energy density, however, does correspond to that of an intermediate temperature, ((774+3004)/2)1/4 K or about 253 K. The mix of different frequencies will not match a true 253 K spectrum, however.
Mike W.
(published on 03/30/2015)