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.
Lets look at velocity or speed.
If air is blowing fast across a component, then many molecules have a chance to grab some heat from the surface. If there is no velocity, then you are back to natural convection, which really has a little bit of velocity because some molecules are going skyward. The flow rate of air through the case is what takes the heat out of the case, the final leg of the journey when you imagine the heat being created inside the electronics, being conducted to the surface, then being moved into the air within the case by convection, and finally being exhausted out into the room. More air moving through the case means less temperature rise of that air, thereby increasing the efficiency of the forced convection. To understand why difference in temperature is important, lets imagine the 2 extremes.