THERMAL CONDUCTION

Preamble:

In all the following articles we assume that physical phenomenon coming into play are stationary, i.e. none of the parameters considered will vary with time and the system is at equilibrium.
Of course reality is not like that, the processor will generate more or less heat according to whether it is more or less loaded.
But then why neglect time related variations ? Eh, well firstly because it greatly simplifies things and secondly because it roughly does not change anything in the final analysis. It is just enough to be concerned with what occurs when the cpu is fully loaded, when it generates the most thermal power, because what is valid under these conditions will also be in others.

Heat is not treated alone without reason, it propagates from hot to cold parts and tries to restore the thermal equilibrium, in other words so that the temperature is everywhere homogeneous.
For all the materials ( solid or fluid ) this phenomenon results, when the body is motionless, in what is called the Fourier's law. In order to be able to establish the principal characteristics of conduction, we will consider the simplest form of the Fourier's law, applied to a very simple geometrical form, a very simple plate, which is heated uniformly on one of its faces.

We thus take a plate of some material, of thickness L ( in meters, m ) and with both greater surfaces having the same area A ( in meters squared, m² ) but having different temperatures. Other surfaces are supposed to be assumed thermally insulated so that all the heat flow which enters one of the large faces, exits from the other. Once again reality is different, the side faces will be generally exposed to the ambient air which will absorb heat, but so little that we can, without problem, adopt this assumption without modifying the range of what follows.