Foreword, why cooling ?

As a general rule, everything that consumes electricity heats up, this is called the Joule effect. That's the electric energy which changes into another, thermal energy or heat ( which is measured in Joule J ). A processor does not escape this rule, unfortunately, it generates heat.
Rather than heat, we use thermal power to measure this phenomenon, which is the quantity of heat released during one second ( in Joule by second J/s or Watt W ).
The thermal power is a significant parameter, which is the one that is conveyed along the path: processor - > cooling system - > ambient air. If a processor releases a thermal power P, the ambient air ultimately receives that same thermal power P.

For a given processor, it depends on three parameters :

• the electric voltage provided to the cpu
• the frequency
• the load

The released thermal power is proportional to the frequency ( if each cpu's cycle needs a certain quantity of energy, the more there are cycles in one second, the more the power dissipated by Joule effect is significant ), to the load and to the square of the voltage. If these parameters increase, the thermal power increases.
Here things are getting worse ! because one always seeks to obtain more megahertz ! Furthermore, to stabilize the processor at a higher frequency, increasing the voltage is essential ( to improve the ratio signal/noise, electric noise being a byproduct of heat ), which causes the CPU to produce an even more significant amount of thermal power !

A given cpu will work at a given frequency only if its temperature is lower than a certain value and the higher its frequency is the lower this value is. But going down very low is useless, the silicon of the processor becomes insulating ( nevertheless it's a long way to get there ).
Thus temperature a very sensitive factor, for this reason one wants to cool.

We will start with the basic concepts such as conduction, convection and a little bit of radiation, just to say that it exists because it plays only a negligible role for what concerns us.
Next, basic concepts about the fluid's interaction with cooling system components will be addressed, including head losses, fans and pumps.
We will see then the applications of these principles to systems daily used to cool processors like heatsinks and waterblocks, heat exchangers, phase change systems ( refrigeration, heat-pipe, evaporative cooler/bong ) and finally tecs.
The goal of these articles is to have the necessary basis to describe the principles of the various cooling systems available.