air flow direction on CPU heatsink.

[o770]

i just recently noticed the CPU fan could be set to suck the air despite blowing it onto the heatsink. Could that be done with my FOP-38? when isnt that modification recommended?
thanks.

[badgers]

are you asking if you should blow air on a heat sink or suck air from the heat sink?

if so the answer is a qualified maybe :)
this desicion is based on the construction of the heat sink, and its thermal conductivity.

think of it this way. if you suck air, the coolest air will be at the base of the heat sink. The air will get warm down at the base of the heat sink. This warmed air goes past the fins of the heat sink but can't cool the fins because the air is already warm. small thin fins IMO do best when air is blown at the heat sink.

if you have thicker fins then maybe sucking air would be better. We have a computer program that can model thermal conduction in materials and fluids. I would think that HSF manuf. have it also. I think that the current designs have been constructed so that they work best with air flow at the heat sink.

PS most of this goes out the window if you have a huge air flow rate. Example maybe the HSF was designed for a fan of 30 CFM. If you flow 90 CFM the air flow direction will become insignificant. The air is just moving to fast.

[lennytiger]

If it is a copper heatsink it is best to blow air down because copper heats up quicker than alluminium..


When your coffee or you food is too hot what do you do, blow it so it gets colder or suck it???

Thats just an example but the immediate human reaction to something (like food) that is hot is to blow it to cool it down.

Try sucking air away from your heatsink and see which is the best direction for you though my guess will be blowing down on to the Heatsink...

[o770]

well, what made me to think on reverse the direction of the air was the temperature inside my case which is not that cool. maybe sucking air away from the heatsink would cool it a little bit more in spite of blowing hot air onto it (that would never cool the food too ;)).
FOP-38 has a very powerful Delta fan: wouldnt a high air flow rate in the sucking direction be better into a hot ambient?

[Intraveinous]

If you're not afraid to cut your case, just cut a blowhole above the cpu, and run a duct down to the heatsink. That way, you are always getting cool, outside of the case air blown on your heatsink.
As far as suck or blow, (On the heatsink you sicko :D) it depends on the design. Many of the Alpha fans used fans in suckin positions. The Zalman CNPS-5000 and 5000+ also use suction. The difference with these was that they included a shroud around a large portion of the heatsink. The shroud keeps it so the air comes in at the bottom and flows up and out.

Sorry for the bad art...
Peace
John