7th March 2008 - 05:50 AM
QUOTE (PIATLAS+Mar 6 2008, 03:26 AM)
Thermal superconductivity is possible because `phase state teleportation'
between `quantum entangled materials at distances'
is possible and has been demonstrated in laboratories along with `quantum computers'
utilising the effects.
Yeah, but the trick would be to build something of reasonable size where every atom in it's entire structure is entangled with every other atom. And even if you manage that, if I'm not mistaken entangled atoms tend to decouple.
We might be a few steps closer once we figure out how to take nano-tubes and splice them end to end in continuous strands. Or simply make continuous strands of them in the first place. The next step would be entangling every atom to every previous atom during formation. At least that's the theory I've been playing with.
Even if we could only manage half a millimeter strands, strapping a few million of those side by side, and then layering them could create some seriously useful devices.
8th March 2008 - 03:33 AM
Electric superconductors do not conduct heat well, interestingly enough. I haven't read much about this deviation from metals' behaviour (where both conductivities are just proportional), but I'm wondering if this could be a key to understanding superconductivity.
Superfluid helium does superconduct heat, and is the only one to my very limited knowledge. Zero thermal resistance. This has more unexpected consequences, including on the movements of He.
Among normal materials, monocrystalline silicon conducts heat very well - better than copper. Carbon nanotubes could be even better, and this would be extremely welcome, even at high kg cost, for instance in thermal paste for processors. And some ceramics, like AlN (or the disliked BeO) are almost as good as copper but electrical insulators, a much appreciated combination.
9th March 2008 - 11:17 PM
Oddly enough I hadn't looked at superfluids. Now I'm going to have to find out if they've managed anything above 2 kelvin. That's a wee bit chilly for every day use. That is the effect I was looking for, the inability to create a temperature gradient.
10th March 2008 - 02:48 AM
I know very little about them.
From what I've read, only He4, He3 and Li6 have been observed to be superfluid. He4 has the highest temperature with 2K, but fermions like He3 (3mK) and Li6 become superfluids as well.
You may still read the story of Bose-Einstein condensate. People try to salvage it for fermions with Cooper pairs like for superconductors... Though the story of Cooper pairs is less and less fashionable for superconductors.
Put clearly: No theory.
And probably nothing known above 2K.
10th March 2008 - 03:01 AM
Hey, if you have engineering goals, the solution is called a heat pipe. Used in some Cpu coolers.
You know? A sealed tube (but could be another form) filled with a liquid and its vapour. Something like a felt or a sintered metal part helps the liquid move from one end to the other through capillary action.
Because the tube is sealed, the pressure of liquid+vapour adjusts to the temperature. At the warmer end, the liquid evaporates. At the cooler end, the vapour condensates. Capillary action lets the liquid circle back.
As long as the pressure is equal in the whole pipe, so is the temperature, since the liquid/vapour equilibrium determines completely the relation between both. The heat pipe does it - or in other words, conducts heat efficiently - by absorbing a lot of heat when evaporating.
Only limits: The liquid must arrive quickly enough to absorb the heat, and the temperature must be compatible with the liquid state.
10th March 2008 - 03:14 AM
You asked if some theory precludes a material to be a thermal superconductor...
I would be very wary of any such theory.
All theories about the absence of electrical resistance are grossly false for some material.
Hence, all theories about the presence of electrical resistance are false.
Thermal resistance is linked to electrical resistance in metals.
So I suspect all the stuff based on phonons and crystal imperfections they tried to explain me at school and university is plain crank.
What is experimentally observed:
- Conductivity improves at low temperatures
- Chemical purity improves the conductivity of metals at low temperatures
- Monocrystals conduct better
- Isotopic purity improves the conductivity. For instance, diamond made with less C13 is even better.
Beyond that, no solid observation for what I know.
23rd March 2008 - 12:02 AM
Hey, is there something like thermoelectric effects (Peltier and Seebeck) between superconductors?
At least for low temperatures, a closed loop of two electric superconductors would make a thermal superconductor between both junctions. As long, thin, efficient and fast as you want.
And if there are thermoelectric effects: why don't we observe them within a single superconductor, as its chemical composition can't be perfectly homogeneous? They should lead to very high thermal conductivity, which isn't observed.
24th March 2008 - 01:27 PM
Superconductors only have a zero resistance to electron movement. Thermal energy on the other hand takes time to transfer from atom to atom. From what I've been able to gather, only a supersolid is able to superconduct heat. And right now, the only evidence for supersolids even existing, is under some scrutiny. And even the alleged materials are only supersolid below 0.2k. Not exactly a useful temperature range...
28th March 2008 - 02:30 AM
Well, that's something (one of the so many things) I don't understand in superconductors.
In metals, heat is conducted by the mobile electrons much more than by the lattice. That's why metals conduct heat well. That's also why the ratio between thermal and electrical conductivity is a constant for all metals.
So as the electrons seem to be so mobile in superconductors, why the hell is the thermal conductivity low? One more difficulty I have with the BCS theory.