Between a Solid Surface and a Gas or Fluid Following through with the above example, convection is the process of moving heat of off the heat sink fins and out into the air within a computer case. Convection is the heat sink surface heating the air which is closest to the surface, followed by the replacement of that newly heated air with some other nearby air which has not been heated yet. Repeat until cool. When the air heated by a surface rises up by itself, it is termed natural convection. If air is blown over a surface by a fan, it is called forced convection.
Fins are Natural, but Fans are Forced.
Computers use forced convection for cooling because the fan in the power supply pulls air through the case. Also, most CPU s have fans on their heat sinks, which is also forced convection. If we want to improve the cooling of a computer, we need to know about forced convection. Our objective is to take all of the heat created inside of the case and continuously move it to the outside of the case. Forced convection performance for computers is driven by the local velocity of the air, the mass flow rate of the air, and the difference in temperature between the components and the incoming air.