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Worlds dumbest question

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March 28, 2003 10:30:19 PM

Ready for this?

Do heatsink fans on CPU's and graphics chips blow air onto the heatsink or suck it off?

I'm serious. I just got a new P4 2.66 and was looking at the thing at it just struck as something I wanted to know, but didn't.


I'm serious.
March 28, 2003 11:46:14 PM

Aha, a question I'm fairly confident answering :o )

the fans blow cool air on to the processor.
March 28, 2003 11:51:49 PM

Quote:
Aha, a question I'm fairly confident answering :o )
the fans blow cool air on to the processor.

But not ALWAYS. The Alpha PAL8045 heatsinks, for example, are designed so that the fan should be sucking the hot air off of the processor.

But it is true that most of the time the fan does indeed blow air into the heatsink.

<i>edit:</i> I should also mention that if you are buying a new heatsink, it will most likely have some kind of directions/documentation that will tell you which way the fan should be blowing.<P ID="edit"><FONT SIZE=-1><EM>Edited by mister_e on 03/28/03 08:53 PM.</EM></FONT></P>
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March 28, 2003 11:56:13 PM

dammit, so close too. :o )

Really? a fan that sucks air off the heatsink? thats a new one on me. How efficient is it at cooling the CPU?
March 29, 2003 1:58:47 AM

When you draw air through a heatsink instead of blowing onto it you end up with more efficient AIRFLOW due to a drastic reduction of turbulence caused by the air currents hitting the heatsink fins (in addition to turbulence generated by the fan blades). However for this to work, you need to design the heatsink using advanced flow testing methodologies in order to realise maxium benefits. Designs that use a blowing method benefit from the air hitting the base of the heatsink in addition to the fins (and sometimes the chip itself). An improperly designed sucking heatsink will restrict airflow too much and actually result in poorer performance when compared to the traditional designs. so you need to match the fan aerodynamics and flow rate to the topology and flow profile of your heatsink. If you are familiar with external watercooling units, you will notice this concept in practice with sealed enclosures. These enclosures create a wind tunnel effect which allow for a nice improvement in heat dissipation. Additionally, conventional fans tend to have a dead spot directly underneath the motor. The effect of the deadspot is greatly reduced if you introduce a gap between the fan and the heatsink and suck the air off the chip. However the downside to this design is the fact that you are taking relatively warm air off the motherboard and moving it through the heatsink. (also a sucking design tends to have the most airflow near the tips of the heatsink fins, so materials with the best heat conductivity must be used). If you have hot rdram sitting next to your cpu, and/or a hot southbridge/northbridge you are probably better off with a fan that blows onto the cpu.

hope this clears stuff up.

Asus A7N8X ND + Athlong XP 2700(2.17ghz)
Mine is 192fsb x 12 = 2304mhz @ 1.775v
Corsair PC 3500 512 @ 5-3-3-2T :( 
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a c 80 à CPUs
March 29, 2003 3:03:05 AM

That was a most excellent explanation, Stoochie. Was that from you or the cooler guide?

<b><font color=purple>Details, Details, Its all in the Details, If you need help, Don't leave out the Details.</font color=purple></b>
March 29, 2003 3:31:20 AM

WOW!Thanks. And the best part is that it satisfies not only the rank computer amateur, but feeds the "one year of non-major physics" child inside me.

A question though Stoochie (and all): would a sucking fan always have a "hot" center created by the vortex of the fan? Would a blowing fan, given the same heatsink topology, always win out due its chaotic airflow?

I can see the both sides: sucking moves air EFFICIENTY from point A to B, but a blowing fan would expose more air "surface" to absorb heat.
March 29, 2003 4:34:13 AM

yes. the dead zone of any standard fan is a issue, but its one we have to live with it.

there are tip driven magnetic fans that have little or no deadspot... but these are restricted to medium to slow speeds.

<b>Damn War! I'm too young to watch other people die!</b>
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March 30, 2003 1:44:59 PM

i learned all this crap when i was looking to get a cooler for myself and using common sense coupled with my physics classes (gas dynamics). I like to read up on everything i buy and spent a considerable amount of time reading about heatsink design. After all my research i decided to get a thermaltake cpu fan/heatsink for now and save up for watercooling, i like the performance and the fact that its(watercooling) almost silent. (inaudible if done right)

"A question though Stoochie (and all): would a sucking fan always have a "hot" center created by the vortex of the fan? Would a blowing fan, given the same heatsink topology, always win out due its chaotic airflow?"

The sucking design is the design that sucks the air through the heatsink and off the cpu, this design is less affected by the fan deadspot IF PROPERLY MATED to the heatsink. The idea is that the fan will create negative pressure which will "suck" air through the entire heatsink. A blowing design will push air into the heatsink but suffers more from the deadspot. I think that overall, the pushing designs tend to have more cooling power since they can benefit more from your in case airflow and the fact that the base of the heatsink gets a good bit of that flow, while the sucking designs draw relatively warm air from the surface of the motherboard and the heatsink fins get most of the action.

If you look around, you will notice that the hestsink/fan combos with highest performance are usually pushers.

However, i would expect a sucking design to be quieter since alot of noise is caused by turbulence around the fan blades. But dont take my word on this because i didnt research this aspect and completely guessing, besides really good fans are designed with computer software with a focus on reducing the noise from turbulence as much as possible.
a b à CPUs
April 1, 2003 6:42:13 AM

Yes, very detailed, but completely wrong!

<font color=blue>Watts mean squat if you don't have quality!</font color=blue>
a b à CPUs
April 1, 2003 6:53:04 AM

You've learned nothing. The only reason Alpha uses a pull fan is to be different.

1.) Fans draw air from the sides, so sucking actually increases the "dead spot".
2.) Compressed air is more dense, and dense air has more cooling capacity
3.)Because fans blow forward, the air can travel all the way to the base of a heatsink when the fan blows. Even though it's not aerodynamic, the striking air on the base creates a circular flow pattern on the base, and is remixed with other air as it escapes from the side. In the suck pattern, the base is a "dead spot", where in the blow pattern, it's a spot of high turbulance.
4.) Alpha tries to get around the pull from the side problem by using a skirt. In this configuration, most of the cooling area is dead air, with the skirt itself receiving most of the cooling
5.) Air near the board is hot from other chips, therefore the skirt puts the area from which air is pulled into a higher temperature zone. You're pulling warm air instead of pushing cool air.
6.) Air does not like to be pulled, see density in #2
7.) All the things I've said have been proven in practice on ALPHA sinks! Many sites have tested the suck vs. blow patterns and found that Alpha's run cooler if you flip the fan to a normal push configuration!

Don't ask me to look those sites up as this is all stuff rehashed from the same argument 2 years ago. I won back then and I don't think physics have changed since.

<font color=blue>Watts mean squat if you don't have quality!</font color=blue>
April 1, 2003 10:25:27 AM

Good argument. Well I just want to ask a question here. Now I got two chasis fans, one on the 'window' of my case and the other at the back of the case. The 'window' one I set it blowing into the case while the back one is drawing air out from case, is this a good setup?

You never know how stupid you are until you have done something stupid enough for you to realize it.
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April 1, 2003 1:51:01 PM

I can confirm your story Crashman. I own an Alpha PAL6035 with original a fan set to suck... when I put it to blow it worked better. Though the difference was only a couple of degrees C (I don't remember the exact values... but I can always retest it if you guys want).

In theory with the Alpha heatsink turbulence from a blowing fan would be lower because it traffels the same direction the fins are until it hits the bottom. While with sucking you draw air through the fins... if you've ever seen an Alpha heatsink (the fins aren't in vertical/horizantal patters) you will understand that this creates much more turbulence.

My dual-PSU PC is so powerfull that the neighbourhood dims when I turn it on :eek: 
a b à CPUs
April 1, 2003 5:54:13 PM

Normally it would be great, as the window fan should be over your video card. Of course not all cases are designed like that, but in that situation, the heat that's blown away from your video card should rise and be sucked out by both the exhaust fan and power supply fan.

<font color=blue>Watts mean squat if you don't have quality!</font color=blue>
a b à CPUs
April 1, 2003 6:04:43 PM

You would be amazed at how many people fail to find merit in my arguements simply because I restrict myself to putting everything in laymans terms. The reasoning for this is twofold:
1.) Half the time I can't remember the terminology from my studies, only the concepts. But the concepts are what yeild the results!
2.) It's easier for someone who hasn't studied these things to understand layman's terms.

<font color=blue>Watts mean squat if you don't have quality!</font color=blue>
April 3, 2003 10:07:02 AM

1.) Fans draw air from the sides, so sucking actually increases the "dead spot".

clearly you dont understand the airflow through a heatsink, a pulling design WITH A GAP BETWEEN FAN AND HEATSINK reduces the effect of the dead spot. (granted there must be a shroud around the heatsink/fan junction to produce a wind tunnel like effect)


2.) Compressed air is more dense, and dense air has more cooling capacity

thats exactly what i said, if you actually read my writing you will see that in my conclusion i recommended the pushing design.

3.)Because fans blow forward, the air can travel all the way to the base of a heatsink when the fan blows. Even though it's not aerodynamic, the striking air on the base creates a circular flow pattern on the base, and is remixed with other air as it escapes from the side. In the suck pattern, the base is a "dead spot", where in the blow pattern, it's a spot of high turbulance.

i have clearly stated the effect on the base of the heatsink by a pushing design, i also went to great detail explaining that sucking design places mos of the cooling action on the fins of the heatsink.....are you literate?



4.) Alpha tries to get around the pull from the side problem by using a skirt. In this configuration, most of the cooling area is dead air, with the skirt itself receiving most of the cooling

i dont see how that statements contradicts with what i said.


5.) Air near the board is hot from other chips, therefore the skirt puts the area from which air is pulled into a higher temperature zone. You're pulling warm air instead of pushing cool air.

oh my god, thats exactly what i said, seriously, are you retarded?

6.) Air does not like to be pulled, see density in #2

hmm goes further to support my conclusion that blowing designs are better at cooling.

7.) All the things I've said have been proven in practice on ALPHA sinks! Many sites have tested the suck vs. blow patterns and found that Alpha's run cooler if you flip the fan to a normal push configuration!

ok, again that goes to support my conclusion..are you just contradicting me to hear yourself talk?

Don't ask me to look those sites up as this is all stuff rehashed from the same argument 2 years ago. I won back then and I don't think physics have changed since.

nothing is asked from you, however everythinhg you said here goes to support my conclusions so your claim that my research is wrong goes to toot your own horn. You are arguing with my points by restating what i said in different terms, however in effect you said the same thing. hmmmm....

:) 

Asus A7N8X ND + Athlong XP 2700(2.17ghz)
Mine is 192fsb x 12 = 2304mhz @ 1.775v
Corsair PC 3500 512 @ 5-3-3-2T :( 
Audigy 2, Western Digital 80GIG SE 8meg cache
and Some CocknBalls.
April 3, 2003 2:10:23 PM

Hmmm with a shroud around the heatsink beside the bottom... I wonder how the air traffels.
Would it go through the center of the heatsink (towards the fan's death spot... so that would be strange) Or would it go besides the edges. But I sure bet that would give one heck of a sucking sound. :smile:

My dual-PSU PC is so powerfull that the neighbourhood dims when I turn it on :eek: 
a b à CPUs
April 3, 2003 5:32:41 PM

Gee, I guess a recording of such events would prove the giant sucking sound you hear is NOT U.S. jobs going to Mexico because of NAFTA.

<font color=blue>Watts mean squat if you don't have quality!</font color=blue>
April 4, 2003 4:05:21 PM

Looks like you don't like the 'illegal' immigration.

That sucking sound is is the same as the sound that comes from my hovering PC.

My dual-PSU PC is so powerfull that the neighbourhood dims when I turn it on :eek: 
April 4, 2003 6:21:24 PM

oh, you mean the same one WingDing makes ? :wink:

<b>people are only idiots when they don't realize - when they do it just gets funnier, like a dog chasing its own tail, or like george bush's public address(es)</b>
a b à CPUs
April 4, 2003 7:41:00 PM

I don't mind illegal imigration, it's a small problem, and most of those who do it are productive members of our country.

<font color=blue>Watts mean squat if you don't have quality!</font color=blue>
April 5, 2003 11:07:37 AM

Wingding's sound is laughable compared to that of my case.

My dual-PSU PC is so powerfull that the neighbourhood dims when I turn it on :eek: 
April 5, 2003 8:12:14 PM

I see this has strayed waaaaaaaay off your question... The fans should force air (blow) onto the heatsinks...

To understand why, put your hand about an inch from your mouth and suck air in... feel much? Now blow air out... now you know why.



--->It ain't better if it don't work<---
April 5, 2003 8:14:05 PM

both of you should record the sound and compare :wink: , ehehehe

<b>people are only idiots when they don't realize - when they do it just gets funnier, like a dog chasing its own tail, or like george bush's public address(es)</b>
April 7, 2003 8:56:19 AM

"To understand why, put your hand about an inch from your mouth and suck air in... feel much? Now blow air out... now you know why."

Hmm interesting analogy. Try making one hand into a tube, and then press the other against it and then draw air in, note how the air in your tubed hand gets really cool? now blow, notice how hot air comes out and warms both of your hands?

moral of this analogy? absolutely none. Heatsinks and your mouth are completely different things and should not be compared to fans.

Saphire 9700pro (400gpu/333mem)
Asus A7N8X ND + XP 2700(192fsb x 12 @ 1.775v)
Corsair PC 3500 512 @ 5-3-3-2T :( 
Audigy 2, WD-SE 80GIG
April 7, 2003 3:00:36 PM

"Hmm interesting analogy. Try making one hand into a tube, and then press the other against it and then draw air in, note how the air in your tubed hand gets really cool? now blow, notice how hot air comes out and warms both of your hands?"

That's because you are blowing 90 degree air on them. (i.e. nearly at body temperature)

Try the same experiment with a fan... put your hand about a couple of inches from the suction side of the fan... feel much? Now put your hand on the blower side of the fan... guess what... lots and lots of cool air.




--->It ain't better if it don't work<---
April 8, 2003 10:20:56 AM

again you are neglecting the importance of the shrowd as the one used in the alpha heatsink, so putting a hand behind a fan would accomplish nothing as there is insuficent directional flow. Also the shrowd is where an under-pressure develops from the fan and draws a stream of air to equalise it.......

If i were to hire you to design me a heatsink and fan combo i would fire you immediatelly after seeing you standing with your hand in a fan. Or blowing on your fingers for that matter. Its not quite the same you know.



Saphire 9700pro (400gpu/333mem)
Asus A7N8X ND + XP 2700(192fsb x 12 @ 1.775v)
Corsair PC 3500 512 @ 5-3-3-2T :( 
Audigy 2, WD-SE 80GIG
April 8, 2003 5:15:27 PM

Yet, strangely, I've designed cooling systems for industrial robotics.

Go figger.


--->It ain't better if it don't work<---
April 8, 2003 5:32:40 PM

Uhm to be honest that shroud Alpha uses is a POS. It has small holes in the corners and it is much to short to be effective in a sucking setup. In a blowing setup they are slightly more effective because they help to bundle the air when it comes out of the fan... but again they should be longer.

My dual-PSU PC is so powerfull that the neighbourhood dims when I turn it on :eek: 
April 27, 2003 11:04:38 PM

haha this is an old thread but id like to add a link that should silence anyone who thinks that blowing heatsink designs are inherently better:

http://www.dansdata.com/coolercomp.htm

Its the very first heatsink to be reviewed on the site
here is an excerpt from the review:

"...Topped with a quite ferocious Delta AFB0612EH, which has a run power of five-odd watts, the 3A Cooler sink did well; 0.54°C/W. Unusually, this heat sink is happier with its fan sucking air up through it, rather than blowing air down onto it; with the fan turned around, the cooler clocked an even better 0.52°C/W. I used the same fan orientation for the subsequent tests."

hmm note the big, efficient shroud that i rave about so much.


Saphire 9700pro (400gpu/333mem)
Asus A7N8X ND + XP 2700(192fsb x 12 @ 1.775v)
Corsair PC 3500 512 @ 5-3-3-2T :( 
Audigy 2, WD-SE 80GIG
!