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Old 13th July, 2004, 07:29 PM
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fan direction

Which is most effecient for cooling a heatsink, having the fan blow downward into the heatsink or outwards away from the heatsink?
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Old 13th July, 2004, 07:41 PM
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Do you mean for something like a side panel fan? If so, blowing in at the heatsink would be the prefered way.
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Old 13th July, 2004, 07:53 PM
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no i mean for the actual fan on top of the heatsink.
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Old 13th July, 2004, 07:58 PM
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That depends on the heatsink. The volcano 12 as well as all of the Alpha HSF are designed to such air off of the HSF. They have shrouds so that the air is drawn in at the bottom of the HSF and exausted out the top. This is more efficant and causes less noise than if you turned the fan around.

Most other HSF do not have any kind of shroud and if the fans were set to suck then the air would follow the path of least resistance and would be sucked in close to the fan were it wouldn't do much good. So those fans work best blowing into the HSF.

Unless of course you are talking about a case fan mounted on the side panel over the HSF. The the fan blowing in and feeding the HSF with fresh cool air would be most efficant.
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Old 13th July, 2004, 09:53 PM
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Generally having the fan blow onto something is more effective. Fans cope better with the air resistance on the exhaust side.
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Old 19th July, 2004, 05:55 PM
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Quote:
Originally Posted by Áedán
Fans cope better with the air resistance on the exhaust side.
Hmmm... without disagreeing that blowing down into a HS might be what they're designed for I'd have to ask if you're sure about a blanket statement like that.
I suspect that, without a shroud, gas inertia may play more of a role than the ability of a fan to push or to pull.

As a case in opposition, watercoolers often see lower temps when they pull air through a radiator rather then push (both cases using a shroud to ensure the flow actually goes through the radiator - and both cases using the same fan at the same voltage). I'm not sure this proves anything either, just opens the situation up to uncertainty...
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Old 19th July, 2004, 06:27 PM
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I believe the profile of the blades plays a role. But your average fan draws air in at the back from a wide angle and pushes it out the front at a narrower angle.

Because water rads are normally much wider than a HS they can benefit from having a fan above pulling air through the fins. Whereas most heatsinks need the air to be directed to the center which is likely to be the hotest part of the HS.

So, in simple terms the 'blow side' gives spot cooling and the 'suck side' gives wide area cooling.

I doubt that you could effect spot cooling by use of a shroud due to the profile of the blades, it just allows better control of the air flow across a square shaped radiator.
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Old 19th July, 2004, 06:32 PM
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I think Kaitain could probably give an explanation based on the fluid dynamics, as that's his thing. I certainly can't!
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Old 19th July, 2004, 06:50 PM
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the fan will work better pulling than pushing..it's all about the bushings/bearings used. This, however does not determine which is best.
it really al depends on how the air flows through your case.
example..may case has LOW side fans....so if my hsf was blowing onto the heatsink, it would be fighting the side panel fans...not efficient.
however..if i cover the holes and use no side fans, the pushing against the heastsink works best.
then you have to factor in cables and all that garbage....
best thing to do is try it and monitor your temps...every situation is different.
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Old 19th July, 2004, 07:01 PM
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I don't understand how the bearings will affect this - or do you mean when the polarity is reversed?

Are your side fans intakes or exhausts?
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Old 19th July, 2004, 07:08 PM
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how does the fan spin on the shaft? that is what i mean. different types of bearings/bushings have differing strengths when force is applied across them...
some fans work better @ pulling than pushing.
i guess i'm trying to say what type of motor is used. and the sideways force against the bearings due to the load of the fan....
my side windows are intakes...fresh air for the vid card....
kinda reconsiderring that tho becuase of the big-ass copper backplate the air gets heated by the card and southbridge before hitting the cpu...to the pont that if i tahe the door off the cpu will lower 2c and the southbridge & vid card go up 3C
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Old 19th July, 2004, 08:17 PM
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as well, i have one of those barrel fans in the back....it intakes from top and bottom... so it seems to catch the splash if air that hits the case from the cpu fairly well....if i had a normal fan i'm sure things would be different.
basically my case cooling follows what thermaltake as in thier cases... but with a slight variation...and i have yet to add the 2 hole for intake in the top....my psu doesa reall good job of taking any hot air out of the top, so i want to force the air that rises slightly more to the rear of the case, and then i will increase the speed of the rear fan.
also, if i set my cpu fan to max(5100rpm)i get higher temps than @ 4250 (2C)
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Old 19th July, 2004, 09:00 PM
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Quote:
Originally Posted by cadaveca
also, if i set my cpu fan to max(5100rpm)i get higher temps than @ 4250 (2C)
Just goes to show that trial and error is the way to do it.
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