Two or three types of heat transfer?

[seb7]

Heat transfer: Conduction - Convection - Radiation, but I was wondering if conductive transfer is actually radiation transfer, but at contact distances; well not really contact since no material actually touches each other (at a quantum level).

So, is conductive heat actually being transferred by radiation?

 

[BvU]

Yes. So is convection -- with a little help from gravity.

 

[DrClaude]

So, is conductive heat actually being transferred by radiation?

No! Conductive heat transfer is through direct contact because of, e.g., coupling (for example, in a solid where local vibrations propagate to neighboring lattice sites) or free electrons in metals. No radiation is ever emitted or absorbed.

 

[BvU]

The governing force in collisions between molecules is electromagnetic, hence my slightly ironic first reply.

 

[DrClaude]

The governing force in collisions between molecules is electromagnetic, hence my slightly ironic first reply.

Fair enough. The irony was lost on me.

Indeed, what is convection but conduction + gravity?

 

[sophiecentaur]

This is another classification question which can be useful in as far as it makes you think. But fitting actuality to arbitrary rules that are learned by rote is a bit of a dead end activity.

 

[BvU]

@seb7 : keep wondering !

 

[Dale]

So, is conductive heat actually being transferred by radiation?

I would say no. The reason that we split heat into conduction, radiation, and convection is that different equations are used. You could say it is all radiation but then you would have to distinguish between contact radiation and distant radiation in order to use the right equations

Since we have to make that distinction anyway, we may as well use the words “conduction” and “radiation” to do so.

 

[sophiecentaur]

The reason that we split heat into conduction, radiation, and convection is that different equations are used.

That's a good observation and effectively sorts out the problem.

 

[nasu]

The governing force in collisions between molecules is electromagnetic, hence my slightly ironic first reply.

Electromagnetic interaction is not equivalent to "radiation". The atoms in a solid transfer thermal energy without emitting any electromagnetic radiation.

 

[BvU]

Care to elaborate ? Subtle differences between virtual photons and (almost) on-shell photons ?