CPUFan Blows towards the Heatsink?Or away?Anyone?

[KevinGuy]

Ok I just recieved my Heatsink and fan ( Thermalright SK6+ w/ 7000rpm fan )

Now the question is, Do i face the fan to blow air at the HeatSink, Or away from the heat sink? I am thinking towards the heatsink personally, But I could be wrong so I am posting.

Thanks

--Kevin<P ID="edit"><FONT SIZE=-1><EM>Edited by KevinGuy on 11/21/01 00:49 AM.</EM></FONT></P>

 

[bgates]

The fan faces up, to pull heat away.

-¤ Shut the f*ck up or go AMD ¤-

 

[Era]

Make it blow at the hs and you get about 2C lower temps.

 

[OldBear]

ERA is correct. Fan blows toward heatsink. Only heatsink mfg. that claims or recommends otherwise is the ALPHA site. They say the ALPHA Pal 8045 works a little better (@ 1 degree C.) blowing up.

<font color=blue>Will Rogers never liked me.</font color=blue>

 

[svol]

OldBear is right about Alpha recommending to let the fan blow up. I have a Alpha PAL6035 with Delta HP 7200 rpm fan, and I have the fan blowing upwards because Alpha claims that this works bests and produces less sound, it also keeps heat away form your mobo.
You have to try to see what works best for you.

Do not make illegal copies of this post

 

[bront]

I've seen tests by independant reviews that agree with Alpha, but they did point out that they are the only one that recomends this.

If you want to pull heat away from your MB, get an intake fan or outake fan to move the air along.

Chesnuts roasting on an open CPU
Bill Gates nipping at your wallet

 

[MadCat]

I'm going to take a guess...

For the Alpha heatsinks (at least on mine), there's a shroud that covers the heat sink fins. The fan draws air through the fins from one the side of the heat sink producing a laminar flow of cooling air that is more efficient at cooling as opposed to a fan on schroud-less heatsinks. Cooling on shroud-less heat sink is achieved by blowing air down on the heat sink but this causes eddys resulting in inefficient cooling. Blowing into a shroud covered heat sink would still tend to produce (more?) eddys, so it is best to draw air out. Follow the manufacturer's recomended directions.

Is this a good guess?

 

[Guest]

I've actually tested this myself on several heatsinks. I found that the Alpha does work best when the fan is blowing off the heatsink only because the heatsink uses a shroud. The shroud only allows the air to flow at the lower part of the heatsink and base. This is beneficial because the lower part of the heatsink is where heat is the greatest. Without a shroud the fan should be blowing on the heatsink, thus blowing air onto the lower part of the fins and base.

If I were in your position I would put a shroud on the heatsink. Packaging or electrical tape works very well, you will want to cover a little less than half of the heatsink's fins. As one person has already stated, if you are putting the fan so it blows off the heatsink be sure to have an exhaust fan nearby. Also previously stated, having the fan blow off the heatsink lowers your motherboard temperatures considerably.

 

[MadCat]

Actually, on my Alpha, the fan is on one side, and the place where air is allowed to come in is on the opposite side. It's not on the top of the heat sink.

[good guess]
Point I was trying to make is:

Heatsinks Without a Schroud - They usually have (I believe) a lower profile fins and have a fan mounted directly on top blowing down. It's more efficient for the fan to blow air in as the frontal wake produced by the fan is large enough to get at all the contact area. If the fan was drawing air from the heatsink in this model, there will be air current leaks which don't contribute to the cooling. Making a schroud for the purpose of drawing air out for traditional heatsinks may be difficult: 1) profile is lower to begin with, 2) the heat sink contact area blocks the opening on the opposite side requiring air to enter in a small gap from all side. A relatively static volume of air may be created near the center of the heat sink assembly if this idea was attemped.

Heatsinks With Schrouds (Alpha) - They tend have a square side profile because the fan needs to be mounted on the side to draw air through the fins. The exhaust part of the fan tends to creates eddys, the intake part of the fan tends to create linear flow. So the air is drawn out for maximum cooling effeciency.

Order of effectiveness for Alpha type heatsinks:

1) Cubical heatsink, fan on the side, with schroud, drawing air through the fins (linear flow for maximum cooling efficiency).
2) Cubical heatsink, fan on the side, with schroud, blowing air through the fins (outflow wake tends to produce eddys reducing cooling efficiency).

Order of effectiveness for traditional type heatsinks:

1) Low profile heatsink, fan on top, no schroud, blowing air through the fins (outflow wake is turbulent enough to get at the surface area of the heat sink).
2) Low profile heatsink, fan on top, no schroud, drawing air through the fins (air current leaks will not contribute to the cooling efficiency).
[/good guess]

Sorry for being so verbose. This is an interesting topic.

 

[Crashman]

Blow down.
1.) The air over an inch away is cooler than the air close to the motherboard.
2.) Fans blow forward but pull from the sides. A heatsink designed for pulling air requires a shroud, such as on the Alpha. But because of reason 1, many Alpha owners claim LOWER temps by reversing their fans! And most heatsinks are unshrouded.

What's the frequency, Kenneth?