crystals and heat

[Anomalistic Thought]

I was doing some random brainsotrming about ways to create better insulation for ultra cold liquids(i.e. liquid N2 and h2), and was wondering if there was any way to create a substance, most likely a crystal, that could rout heat like a fiber optic cable? That is instead of conducting into the liquid, it radiates out of a specified area? Is there any way to do this without breaking the laws of thermodynamics? Thankyou in advance.

[Qfwfq]

I don't see why the laws of thermodynamics would be broken at all. It doesn't strike me as being a thermodynamic matter at all, heat conduction isn't thermodynamics.

Wrap a wire of an ideal heat conductor with a sheath of ideal insulator... conceptually that's the idea, there's no contradiction. In practice, good conductor inside and bad conductor outside.

[UncleAl]

Fiberoptic cables leak energy via many mechanisms. Frustrated total internal reflectance spectroscopy is based upon it. You also get parasitic Raman modes in any material medium propagating photons, as well as absorptive losses. Any medium with a refractive index greater than 1 must have absorptive loses by definition - absorption re-emission is how refractive index arises.

The three laws of thermodynamics:

1) You cannot win - conservation of mass-energy from the homogeneity of time plus Noether's theorem.

2) You can only break even on a very cold day - entropy and the statistics of very large ensembles, Carnot cycle. When was the last time you flipped an honest coin heads 10^20 times in a row?

3) It never gets that cold. Absolute zero cannot be achieved in a finite number of cycles; division by zero is undefined.

Blackbody radiation. You are horribly wrong.

[Qfwfq]

1) isn't a law of thermodynamics. I doubt AT is interested in such subtleties as the Raman effect.

Originally Posted by UncleAl

Any medium with a refractive index greater than 1 must have absorptive loses by definition - absorption re-emission is how refractive index arises.

AT is talking about thermal energy. Is less heat going to be re-emitted than was absorbed? Once the bugger has reached regime temperature, that would imply some chemical changes or something. Material degradation of some kind, perhaps, OK, but that would imply very tiny absorptive losses.

[Anomalistic Thought]

The problem is that the large heat difference between the liquid and the outside enviroment is great enough that insulators like rubber still conducte enough heat to cause the liquids to boil off(especially Hydrogen, which is kept at -270 degrees C). I was thinking if something could be layered to make it more dificult for the heat to conduct through each succesive layer, instead causing some amount of it to reflect off of each layer. This might not be possible, because the inside of the tank will be extreamly cool compaired to the skin of the tank, and the system will "want" to balance out the heat imbalance.

[Qfwfq]

Originally Posted by Anomalistic Thought

and the system will "want" to balance out the heat imbalance.

Obviously, this is the whole matter behind heat insulation. The best insulator, concerning thermal agitation, is the vacuum. No material at all, hence no thermal agitation or even convection. There remains radiation. The walls of a thermos are highly reflactant, this minimizes radiation for given temperatures. Both facing surfaces should be the same, the less a surface radiates, the less it absorbs radiation.

No material container will be perfectly insulated. Liquid N2 will always evaporate a bit for a given pressure.

[UncleAl]

I was thinking if something could be layered to make it more dificult for the heat to conduct through each succesive layer, instead causing some amount of it to reflect off of each layer.

It's been done - superinsulation. Hundreds of layers of very thin aluminum foil or aluminized mylar are separated by very thin spacer like open weave gauze, the whole under a hard dewar vacuum. There is no convection. Thermal conduction is frustrated by the small net area of contact layer to layer. Blackbody energy emission varies as the fourth power of the absolute temp, and at any wavelength absorptivity must equal emissivity (First Law). Hundreds of layers of mirrors eventually gradient cool, and thermal conductivity drops to essentially zero.

http://helios.augustana.edu/~dr/102/nmr-cutaway.html
pictures
http://pc16002.pharmazie.uni-marburg...struction.html
text

[Anomalistic Thought]

Originally Posted by UncleAl

It's been done - superinsulation.

Thanks, this is really helpful. I was hoping that something like this already existed.