heat conduction mechanism

[rayman]

Hello! I am supposed to explain the behaviour of the thermal conductivity of tungsten. I have plotted the relation

http://img340.images...76/heatcond.jpg is also experimental data

Temp[0 10 50 100 300 500 1000 2000 3400]

and thermal conductivity coefficient

0 97,1 4,28 2,08 1,74 1,46 1,18 1 0,9]

Can someone explain the mechanism to me? Why does the thermal conductivity reaches its maximum for T=10K ? and after that it gradually decreases and after some temp is behaves almost like constant?

How this can be explained taking free electrons and phonons into the concideration?

Thank you!

[lemur]

Just a naive guess, but wouldn't any conductor conduct heat more efficiently at lower temperatures because the heat differential (I think I've heard people call this "delta T") is greater between the hot part and the cold part. A chimney drafts strongest in the coldest weather for the same reason, I think. Am I oversimplifying this or is it really as common sensical as it seems?

[swansont]

Just a naive guess, but wouldn't any conductor conduct heat more efficiently at lower temperatures because the heat differential (I think I've heard people call this "delta T") is greater between the hot part and the cold part. A chimney drafts strongest in the coldest weather for the same reason, I think. Am I oversimplifying this or is it really as common sensical as it seems?

 

No, because the constant is separate from the temperature difference. Both factors are present.

[lemur]

No, because the constant is separate from the temperature difference. Both factors are present.

 

Then I would guess that any substance has a temperature where its conductivity is fully expressed and that its maximum conductivity occurs at that temp. Then, I would guess conductivity diminishes as temperature increases due to relative equilibrium between hot and cold poles. Are there materials whose heat conductivity does not chart as a bell-curve or some other curve? What are the factors that influence heat conductivity?

[alpha2cen]

What are the factors that influence heat conductivity?

 

Thermal conductivity is caused by atomic vibration or crystal vibration. This phenomena is also related to thermal melting. If the vibration energy is more bigger than attraction force between the solid atoms, solid will melt into liquid. I think that the cause of the tungsten's high temperature thermal resistance might comes from the low thermal conductivity at high temperature.

Edited January 17, 2011 by alpha2cen

[lemur]

Thermal conductivity is caused by atomic vibration or crystal vibration. This phenomena is also related to thermal melting. If the vibration energy is more bigger than attraction force between the solid atoms, solid will melt into liquid. I think that the cause of the tungsten's high temperature thermal resistance might comes from the low thermal conductivity at high temperature.

That is a redundant sentence. "High temperature thermal resistance" means the same thing as "low thermal conductivity at high temperature." Why does attraction force between solid atoms prevent vibration? Because they vibrate in unison instead of separately? What about different kinds of atoms that vibrate separately but have different thermal conductivity? I always assumed that better electrical conductors conduct heat better because of the same "looseness" between the electrons and the nuclei. In electricity, I assumed this "looseness" translated into fluidity of the electrons; whereas in heat-conduction I assumed the fluidity of the nuclei was facilitated by their "loose" nesting within the electrons.

[alpha2cen]

That is a redundant sentence. "High temperature thermal resistance" means the same thing as "low thermal conductivity at high temperature." Why does attraction force between solid atoms prevent vibration? Because they vibrate in unison instead of separately? What about different kinds of atoms that vibrate separately but have different thermal conductivity? I always assumed that better electrical conductors conduct heat better because of the same "looseness" between the electrons and the nuclei. In electricity, I assumed this "looseness" translated into fluidity of the electrons; whereas in heat-conduction I assumed the fluidity of the nuclei was facilitated by their "loose" nesting within the electrons.

 

I mean thermal stability at the high temperature. The vibration amount is related to the crystal structure of the tungsten, I suppose.

When the vibration energy is very high, the bonds between the atoms may be weaker than before. The broken bondage state of the atom is liquid.

In general , liquid is consisted of freely moving few atom bondages.

There are few literature about freely moving thermal electrons.

More data make perfect theory.

Edited January 17, 2011 by alpha2cen

[lemur]

I mean thermal stability at the high temperature. The vibration amount is related to the crystal structure of the tungsten, I suppose.

When the vibration energy is very high, the bonds between the atoms may be weaker than before. The broken bondage state of the atom is liquid.

In general , liquid is consisted of freely moving few atom bondages.

There are few literature about freely moving thermal electrons.

More data make perfect theory.

I guess I have a lot of lay assumptions about things, but it always seemed to me like crystalization occurs due to the shape of the atoms/molecules. I figured that when they are moving fast relative to their weight, they can't settle enough to nestle together in a certain alignment. What kind of "bonds" are you saying strengthen or weaken and why?

 

I don't know if you need more data to see that electrons don't move freely in any kind of current. If they did, wouldn't there have to be large sources of electrons to input into conductors and wouldn't they be piling up at the receiving end? I read recently in a book by Planck that electricity would be understood in terms of gas dynamics, and that made sense to me insofar as the electrons in a conductor seem to act as gas particles transmitting wave energy. Maybe I misinterpreted what Planck meant with that, though.

 

 

[alpha2cen]

I guess I have a lot of lay assumptions about things, but it always seemed to me like crystalization occurs due to the shape of the atoms/molecules. I figured that when they are moving fast relative to their weight, they can't settle enough to nestle together in a certain alignment. What kind of "bonds" are you saying strengthen or weaken and why?

This is metallic bond. Every protons maintain certain distance in the solid and electrons are freely moving around. If temperature rise, the movement, i.e., vibration energy between protons are increased. At the high temperature the vibration energy is larger than structure maintaining energy, and it would become liquid.

 

I don't know if you need more data to see that electrons don't move freely in any kind of current. If they did, wouldn't there have to be large sources of electrons to input into conductors and wouldn't they be piling up at the receiving end? I read recently in a book by Planck that electricity would be understood in terms of gas dynamics, and that made sense to me insofar as the electrons in a conductor seem to act as gas particles transmitting wave energy. Maybe I misinterpreted what Planck meant with that, though.

 

 

I do not think the rule of electrons is not increased with temperature on the tungsten heat transfer.

 

There are freely moving electrons in the metal.

And, there are many descriptions about the freely moving electrons contribution on the heat transfer.

But their role on the heat transfer is not clearly quantified in the literature.

Are there any difficulties to quantify?

[lemur]

This is metallic bond. Every protons maintain certain distance in the solid and electrons are freely moving around. If temperature rise, the movement, i.e., vibration energy between protons are increased. At the high temperature the vibration energy is larger than structure maintaining energy, and it would become liquid.

You talk about protons maintaining distance and "structure-maintaining energy." What is the cause of structure except the configuration/shape of the atoms/molecules?

 

 

 

 

[alpha2cen]

You talk about protons maintaining distance and "structure-maintaining energy." What is the cause of structure except the configuration/shape of the atoms/molecules?

 

 

 

 

 

Difficult question.

There are many literature about metal composition to strength, corrosion,...

But there are few literature about basic problem.

The theory disclaims the theory I described above, i.e. proton structure and freely moving electrons.

So structure maintaining energy is not simple one but complex combined energy style.

At any rate, it is known that solid heat transfer is related to vibration energy.

[lemur]

Difficult question.

There are many literature about metal composition to strength, corrosion,...

But there are few literature about basic problem.

The theory disclaims the theory I described above, i.e. proton structure and freely moving electrons.

So structure maintaining energy is not simple one but complex combined energy style.

At any rate, it is known that solid heat transfer is related to vibration energy.

It is logical that heat transfers as vibration. Heat is basically kinetic energy of atoms/molecules. "Vibration" implies that the atoms/molecules are basically fixed in terms of their center of mass and are moving relative to that. The question is why their (average) center of mass would become mobile enough for them to flow, as in a liquid. It must have something to do with the viscosity of the electron-clouds/shells changing. What is holding them together strongly enough that it requires a great deal of heat to cause them to flow relative to each other? When they don't melt, what causes one material to insulate better than another? The energy has to go somewhere, right? So why does the heat travel through one material more easily and faster than another?

[alpha2cen]

Till now I have never seen detail molecular mechanism of metal fusion and ionic solid fusion.

Well known knowledges are macroscopic models, i.e., melting temperature, latent heat, ...

Ideal solid model solid is represented as 3 dimensional spring connected material. We have not made ideal metal solid model yet, my guessing.

Edited January 18, 2011 by alpha2cen