Editing Thermal design power (section)

=== Thermal management fundamentals ===

To better understand the problem we must remember the basic concepts underlying [[Thermal management (electronics)|thermal management]] and [[computer cooling]]. <ref name=Cooling_and_Efficiency /> Let’s consider the [[thermal conduction]] path from the [[CPU]] case to the ambient air through a [[Heat sink]], with:

:Pd ([[Watt]]) = thermal [[Electric power|power]] generated by a [[CPU]] and to be dissipated into the ambient through a suitable [[Heat sink]]. It corresponds to the total power drain from the direct current supply rails of the [[CPU]].
:Rca ([[°C]]/W) = [[thermal resistance]] of the [[heat sink]], between the case of the [[CPU]] and the ambient air.
:Tc ([[°C]]) 	= maximum allowed temperature of the [[CPU]]'s case (ensuring full performances).
:Ta ([[°C]]) 	= maximum expected ambient temperature at the inlet of the [[heat sink]] fan.

All these parameters are linked together by the following [[equation]]:

:<math>(Tc-Ta)=Pd \cdot Rca </math>

Hence, once we know the thermal power to be dissipated (Pd), the maximum allowed case temperature (Tc) of the [[CPU]] and the maximum expected ambient temperature (Ta) of the air entering the cooling fans, we can determine the fundamental characteristics of the required [[heat sink]], i.e. its thermal resistance Rca, as:

:<math> Rca=\frac {(Tc-Ta)}{Pd} </math>  

This equation can be rearranged by writing 

:<math> Pd=\frac{(Tc-Ta)}{ Rca} </math> 

where in Pd can replaced by the thermal design power (TDP).

Note that the heat dissipation path going from the [[CPU]] to the ambient air flowing through the printed circuit of the motherboard has a thermal resistance that is orders of magnitude greater than that of the [[Heat sink]], therefore it can be neglected in these computations.