The inner pane is warmer than the fill gas, so gas tends to rise on meeting it. The outer pane is coler than the fill gas, so gas tends to sink when meeting it. Thus convenction occurs.
Convection is never absent as long as there is a delta t, just a question of how much. Narrow spacing reduces it.
It still conducts less. The advantage goes when the unit ceases to be airtight.
NT
Radon should be good.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
I have built OCXOs and other ovenized electronics, under a cover. With close spacing reducing convection, the best insulation is air. Foam, fiberglas, things like that are worse.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
Hmm I've got this image of molecules bouncing around all over the place, to get convection you need some group of them to stay together and get hot... (Sorry that's not a very accurate statement.) It's somehow determined from the Rayleigh number.
But the details are far from clear to me.
We made our own air cooled heat sinks (slots milled in Aluminum plate.) My boss wanted a lot of surface area, so the slots were small... (I can't recall the dimensions 1/8", 3/16"?) Anyway it didn't work very well, slots were too close to get convection started... or something like that.
Convection is confusing. (I wish I had time to study it more.)
George H.
:
iation?
y,
in the kT (~25 meV) range of energies. More complicated molecules have l ots of rovibrational states in that range, so they transfer more energy per collision, which makes them disappointing as insulators.
led with Argon instead of CO2. My copy of the Chemical Handbook has CO2 as being slightly better than Argon as far as thermal conductivity. I would not think that there is enough moisture that carbonic acid would cause prob lems.
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of the bunch; unfortunately it is rather expensive, so is only used in a sm all percentage of the most energy efficient windows (particularly triple-gl azed windows where the thinner space between panes allows a smaller amount of the gas to be used). Carbon dioxide has low conductivity as well, but ca n be reactive when it meets moisture, so it?s not suitable for a gl azing gas. Argon is the next best gas"
I tried that but it didn't last very long.. maybe if the glazing was doped with some Uranium :^)
We use Xenon as a "starter" gas in our Rb discharge lamps. I read somewher e it was better that Krypton, and the spectral lines of Xenon are outside of the pass band of the interference filters (IF) we use. (785-825 nm) (Krypton has some nearby line(s).) (The IF is there to take out the 780 Rb line.)
George H.
it is banned in new ACs but you can still buy it,
and have look at what is in aircans, freeze spray or signal horns..
For the reaction cell in my Ph.D. project, convection got under away at a Rayleight number of 500, and would have got turbulent at 100,000 if the Rayleigh number had ever got that high - which it didn't.
-- Bill Sloman, Sydney
Cool, do you have any idea how to calculate the Rayleigh number for air/ Argon in 12 mm glass? (of course you've then got to tell me what the number means... I've seen lots of numbers quoted for where convection begins.)
George H.
:
adiation?
ity,
it's
aration?)
a Rayleight number of 500, and would have got turbulent at 100,000 if the Rayleigh number had ever got that high - which it didn't.
begins.)
Not any longer. It took a certain amount of poking around in the University of Melbourne libraries back in 1969 to get as far as I did. I did nick my younger brother's civil engineer text "Engineering Applications of Fluid Me chanics" by Hunsaker and Rightmire published by McGraw-Hill in 1947, when h e was going to throw it out, but it doesn't go beyond Reynolds numbers and Froud numbers.
-- Bill Sloman, Sydney
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