Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: McKay on 17/03/2015 12:24:32
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If I have a, say 2*20*30 (cm) box completely surrounded/ insulated by aerogel, where the inside is cooled to 77 Kelvin and the outside is 293 kelvin (room tempeature) - how long would it take for the temperature to equalize (practically, for the inside temperature to reach 293 Kelvin) ? And how much power would it require using, say, peltier coolers, to exactly negate the outside heat leaking inside?
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What is the heat capacity of the contents inside the box? (Is it filled with liquid nitrogen, or gaseous hydrogen, or is it full of lead?...)
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Hmm, hmm, well, its just a thought I had about superconducting computers - keeping the components at temperature they can superconduct. I just wanted to know a estimate - would it be minutes, hours, days.. so, what would be the heat capacity of a superconducting computer?
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Hmm... I don't know what the heat capacity is of computer components. There is the additional complication that the components themselves will produce heat (even if they are superconductive, I think)
I don't know how cheap aerogels are these days, but recollection is that they are quite expensive. Another alternative for insulation is something along the lines of a thermos (or Dewar flask http://en.wikipedia.org/wiki/Vacuum_flask) Basically having a space that is evacuated (to prevent conductive and convective heat transfer), and lined with reflective foil (to prevent radiative heat transfer).
That's how we insulate superconducting magnets (we also keep them cold with liquid helium inside a chamber with liquid nitrogen...)
Also, while there are some ceramic materials that superconduct at liquid nitrogen temperatures (77 K), common materials (like copper) must be at significantly lower temperatures (like 4 K, liquid helium temperatures). I also don't know how these extremely low temperatures will influence the performance of semiconductor components in a computer...
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Ok, well, thank you for that. I know its too expensive for most practical uses for now. And superconducting compuers would be built from materials yet to be seen :) But still - I guess I could rephrase it like this: how much heat does an aerogel leak at such temperature difference? Say, at 0.5 cm thickness.
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After a quick google search I found this: http://energy.lbl.gov/ecs/aerogels/sa-thermal.html
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I don't know how much a quantum computer would weigh (along with all its cooling equipment and interfaces to the outside world).
But aerogels are mostly air, and not very strong mechanically. I would expect that the computer would squash the aerogel flat, and the aerogel would no longer be such a wonderful insulator.