CPU Fan

[Maztrim]

Just a quick question. Is it better to have a CPU fan blowing air on the processor or sucking hot air away?

[Jiggy]

I dont think it matters if it blows on or off the cpu, as long as the end result is the hot air leaving the case, try it and see, there will only be a very small change if any.

[saphalline]

I've found significant differences between the two in general. Fluid dynamics in practice lends evidence to the fact that the air movement isn't the same in both cases. While there is more of a dead spot over the center when the fan blows onto the CPU, more airflow overall gets to the heatsink fins. When the fan blows away from the CPU, the airflow over the heatsink fins can be reduced by as much as 30% using a stock HSF unit, and well over 50% using a larger heatsink like a Zalman! :eek: That's a lot of lost airflow!

So I recommend you have the fan blowing onto the CPU in general. If you're working with a laptop or SFF system, then that might be different with directionally-controlled airflow. But in a desktop environment, the fan should blow onto the CPU.

[Sylvander]

All other things being equal, "Contra-Flow" heat transfer is more efficient than "Parallel Flow".
Contra-Flow...
is where the fluid conducting away the heat is going in the direction opposite to the flow of heat in the fins or tubes or whatever.
Parallel Flow...
Is where the fluid is travelling in the same direction as the heat flow.

The reasons for this are best understood when you see a graphical representation of the temperature differences between the fins and the fluid.
Contra-Flow maintains an almost uniform difference between the two whereas with Parallel Flow the difference is great at the point where the two 1st come in contact and gradually reduce toward nil difference [equal temperatures].

Learned this on an Engineering course->Fluid Mechanics->Thermodynamics->Heat Exchanger Theory.