CPU Fan Orientation

[kronik1]

I feel like such an idiot for asking this, but what direction should the CPU fan turn... I realize it should blow air onto the heatsink, but it can also be rotated.. does this actually play a role?

 

[EKAtBzboyz]

fan blowing air down
heatsink
cpu

that is the normal method

alpha heatsinks are designed to have it opposite:
fan blowing air up
heatsink
cpu

try both ways to see which suits your case better

 

[fluxquantum]

you should not feel like an idiot. i always had my fan blowing upwards until i got my swiftech mcx4000. now i have my fan blowing downward onto the heatsink and cpu. i seems to get good results. during idle i get 28C and during full load i get 35C.

 

[jarsoffart]

I was thinking wouldn't that kind of be counterproductive if you had a exhaust fan right in back of the HSF. I would think the CPU fan should blow out and then the exhaust fan will pull it out. Cool air would be sucked in from the bottoms sides of the heatsink because the fan is pulling air out from there. I currently have my Thermalright SLK-800 fan blowing out.

 

[SaveYourself]

That's an interesting question. The Alpha heatsinks use suction to draw air over the many pins in the heatsink, but the heatsink has a special shroud to direct the air over the whole surface of the pins, not just the tops where the fan's suction can generate air movement. A really high-output fan is needed to get the same performance on a heatsink with the fan sucking and no shroud. This is inefficient and noisy. So on Alphas it is highly advised to run the fan in suction mode, drawing air through the pins rather than blowing air onto the pins. Another thing I noticed is that the metal shroud on my Thermaltake Volcano 9 is suitable for using the fan in suction mode rather than blowing on the fins, though I don't know if there will be any advantage to this.

 

[CaptnKirk]

The physics of thermal radiation say that fans should extract heat away from the heat source, rather than compress air into a heated area.
They should suck.

 

but when the fan sucks, it cools the area of the pins/fins farthest away from the processor (without a shroud) - the air coming into the heatsink to replace air being sucked out doesn't necisarily move over the hottest part of the heatsink = not the most efficient cooling

when the fan blows, all areas of the heatsink get air movement

 

[EKAtBzboyz]

generally you need a shround for it to pull air from the base of the pins/fins upwards therefore contacting most surface area

that is why alpha has the pins shaped how they are, increase surface area added with the shroud to bring air from base of heatsink where it is most hot up

with swiftech (the new "coiled" look...i cant remember the exact term they use, but its the same idea) they are looking to increase turbulence/surface area by forcing air down so the turbulence somewhat speeds up the air (its like being in between 2 very tall buildings next to each other in downtown, gets pretty windy with all the winds and curves)

thats what i think this late at night....it seems to somewhat follow physics

 

[kronik1]

CaptnKirk, I was thinking along those lines but.. I guess I won't know until I try eh. Right now, I'm getting 46C idle, 49C full load.. with the air blowing onto the heatsink.. let's reverse and I'll give you guys the results.

 

[kronik1]

Temps (at least socket temps) are lower when the fan blows air onto the heatsink.

 

[xXgambitXx]

imho, there is no "set in stone" rule about this. everyone should just try putting their fan on one way then flipping it and comparing the numbers.

 

[CaptnKirk]

This should simplify your decision

If that doen't help perhaps

This might



Look Spok, they are using their primative weapons
to kill our crewmembers.

 

[BoomAM]

i have my SLK-800 blowing down on the HS as thats how its ment to be run, i read that in a review somewhere, thats why you can see all the way to the cpu from the top, its designed to both blow on the HS, and directly on the core as well.

 

[beverage]

I have an alpha 8045. I have my fan in "suck mode" currently. I've also had it in "blow mode" before, and it ran only about 1-2 degrees hotter. So as far as my system's concerned it didn't seem to make too much of a difference