How does density affect thermal conductivity?

[aniruddha]

Since the flow of heat in solids happens due to the collision of the molecules with each other, thereby increasing their internal energy, a higher denser material will have molecules closer, does it mean that the thermal conductivity of high density materials will be higher than the lower density materials? If not why?

Example:

Copper - Density - 8940 Kg/m3, Thermal conductivity - Around 401 W/mK

Lead - Density - 11340 Kg/m3, Thermal Conductivity - Around 35 W/mK

 

[Drakkith]

Since the flow of heat in solids happens due to the collision of the molecules with each other...

I believe the main contributor to heat transfer is the collisions between free electrons (in metals) and/or phonons (nonmetals) with the rest of the material or an adjacent material. Phonons are essentially 'vibrations' of the structure, which can be simplified to 'collisions' of molecules with each other.

does it mean that the thermal conductivity of high density materials will be higher than the lower density materials? If not why?

Density can play a major factor, especially in gases, but for solids I think the main factor is the way the material's atoms and molecules are bonded together and their arrangement. For example, diamond is a very good conductor of heat because of it's very ordered structure. Copper is MUCH less dense than lead, but, as you have in your post, the thermal conductivity of copper is an order of magnitude greater than lead.

See here for more: http://en.wikipedia.org/wiki/Thermal_conductivity

 

[mynameisjeff]

It affects The Process of convection because, density is how close molecules are nd the closer they are the faster they can bump into each other and spread heat.

 

[Drakkith]

It affects The Process of convection because, density is how close molecules are nd the closer they are the faster they can bump into each other and spread heat.

Convection doesn't happen in solids.