Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: ZeroPopGro on 13/01/2020 14:17:49
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I met a school teacher who said that metals were good heat conductors for the same reason that they are good electrical conductors - their surface electrons are free to move. Is he correct? If so, what is the relative importance of atomic motion? Do phonons assist in rapid heat conduction in metals?
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He's right: https://www.thenakedscientists.com/articles/science-features/thermoelectric-generators-tegs
The electrons in a metal exist as a delocalised "sea" surrounding the pool of positive protons that are the atomic nuclei. Thus the electrons can move about freely, which gives the material its electrical-conducting properties.
But since these particles are mobile, when they are given thermal energy they will vibrate and transfer their momentum to other adjacent particles; the hotter they are the greater the amplitude of their oscillation and hence the greater the distance over which they transfer kinetic (heat) energy within the material.
Consequently, with some rare exceptions, materials that are good electrical conductors are also good thermal conductors. The electrons, being numerous and mobile, tend to be a major means by which heat is transferred.
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Some of the most efficient thermal conductors are heat pipes, which use the vapor phase, which is not an electrical conductor.
- It takes advantage of the fact that the molecules in a vapor are very mobile
- And that a lot of heat is required to turn a liquid into a vapor (and released when the vapor turns back into a liquid)
- Some of these heat pipes can transport heat 100 times more efficiently than copper metal
Heat pipes have the disadvantage that they conduct heat well only over a narrow range of temperatures.
- In contrast, metals, with their sea of electrons conduct heat well over a very wide range of temperatures
- From almost absolute zero until the metal vaporizes.
See: https://en.wikipedia.org/wiki/Heat_pipe