Newbie Question Suck or Blow ?

[Nosiop]

1) Are CPU Fan ment to blow air through the heat sink or Suck air up through it
2) same with case fans

Thanks for help

 

[dave326]

For a cpu the fan is always blowing on it. As for case fans, the idea is to create airflow throughout the case. Something like 2 fans on the front sucking air in, 1 on the top blowing out the hottest air, and another on the back.

 

[Teq]

Ok... first to answer your Subject line... never blow, you can really mess up somone's bladder that way.

Now about the fans ...

Cpu fans should blow cold air onto the heatsink. This is done for 2 reasons... 1) to prevent heat buildup at the base of the heatsink where the airflow would be less on a suction system and 2) to prevent "cavitation" which makes quite a bit of noise and reduces airflow through the fan.

Case fans are a bit different. These are able to draw air from the relatively large, unimpeded volume of air in the case itself. It is best to have case fans extract hot air out of the upper back of the case. You can add an intake fan to the front as well, blowing cool air in... but then you run into that cavitation problem again and things get real noisey, unless your case has a huge air intake opening right by the fan.


To understand Cavitation.. put your hand near the intake side of a fan, as you move closer, you will hear the air noise increase, the fan will speed up (less loading on the motor) and at some point it will become very noisey, like an airplane propellor.

<b>Just be careful that you don't actually touch a spinning fan... that can really hurt!</b>



<b>(</b>It ain't better if it don't work.<b>)</b>

 

[LtBlue14]

Ok... first to answer your Subject line... never blow, you can really mess up somone's bladder that way.

LOL

--------------
I LOVE DANGER DEN WATERCOOLING, they went out of their way to both personalize my kit and change my order when i needed to, i had to change my sig to give them props

 

[lhgpoobaa]

Both CPU fans and GF's should be set to suck.

Casefans usually suck in at the front, blow out the back.

<b>"If spam wasn't totally bogus, Hotmail users would be well-endowed, slim people with hair who make big money working at home and having great sex provoked by free porn and herbal Viagra.</b>

 

[Lonemagi]

OUch!
:redface:

"Apple is more like the French army. They have great style and class, they often get praised for their valor, and they do everything except win."-<A HREF="http://www.overclockers.com" target="_new">Ed Stroligo</A>

 

[Teq]

Hey... good to see y'all got a sense of humour!



<b>(</b>It ain't better if it don't work.<b>)</b>

 

[Rob423]

quick question, how do you switch the HSF from either blowing or sucking the air? i just installed it and connected the wires....

RIG
Asus A7N8X Deluxe
80gb Maxtor
Lian-Li PC-60
Lite-On 52X
AMD XP2800+
LeadTek GeForce 4 Ti4200 w/vivo 128mb 8x
Hitachi CML174
1 GB Corsair XMS PC3200 Cas2

 

[Teq]

Turn the fan over.



<b>(</b>It ain't better if it don't work.<b>)</b>

 

[NE_Corridor]

I remember reading an article that compared 2 identical hsf units one set to suck and one set to blow and the one one that sucked air performed about 2-3 degrees better. I can't remember where I saw this--maybe hardocp.

Call me Caine.

 

[svol]

CPU fans set to suck the air through the heatsink?!? I don't think that is a good idea PooBaa. As the air will not go through the bottom of the heatsink where it is the hottest.

I really hope that was a typo.

My dual-PSU PC is so powerfull that the neighbourhood dims when I turn it on

 

[Guest]

The data on the Alpha (for the 8045) site suggests that better performance is possible with the fan set to draw the air up through the heat sink pins. It doesn't feel right to me either, but I think they would have tried this experimentally before posting something so contrary to what the rest of the world is saying. Maybe this only applies to those particular heatsinks, I wouldn't know.

 

[Teq]

The problem with suction is that the most airflow will be over the top of the fins, hear the fan; across coolest part of the heatsink. Air is forced into a heatsink so that the most airflow is at the base of the sink, where it's the hottest.

A suction system might work if you were to block off the tops of the pins forcing the air to come in near the base, but about all you accomplish is to reduce airflow so much the fan that can't move enough air to cool the heatsink.

I'd say the suggestion is ill considered.



<b>(</b>It ain't better if it don't work.<b>)</b>

 

[lhgpoobaa]

or did i mean suck from the area above down onto the heatsink?

<b>"If spam wasn't totally bogus, Hotmail users would be well-endowed, slim people with hair who make big money working at home and having great sex provoked by free porn and herbal Viagra.</b>

 

[Teq]

I see... so now you are reversing your story on us are you :tongue:


<b>(</b>It ain't better if it don't work.<b>)</b>

 

[Guest]

<A HREF="http://www.micforg.co.jp/en/c_pal8045e.html" target="_new">http://www.micforg.co.jp/en/c_pal8045e.html</A>

Check the graphs near the top of the page.

For whatever reasons, this site is saying the opposite of what you are saying. That is if I am understanding both you, and the website correctly. BTW I'm not necessarily agreeing with either method, just playing devils advocate.

The fact that they give actual thermal resistances for both configs would lead a guy to believe they have run through the experiments.

 

[lhgpoobaa]

Well What happens most often is that the fan blows DOWN onto the heatsink.
This occurs for the majority of coolers, stock, amd, intel and after market ones.

The only ones that ive seen that suck away are the alpha series and a couple of 3rd party ones.

U can allways try it for yourself.

<b>"If spam wasn't totally bogus, Hotmail users would be well-endowed, slim people with hair who make big money working at home and having great sex provoked by free porn and herbal Viagra.</b>

 

[svol]

I tried it with my Alpha PAL6035 (had the same advice) and according to my readings Alpha was wrong with their advice.

My dual-PSU PC is so powerfull that the neighbourhood dims when I turn it on

 

[svol]

I hope so.

My dual-PSU PC is so powerfull that the neighbourhood dims when I turn it on

 

[bonesdad1]

I think it probably depends on the heatsink. MOST often the fan should blow down into the sink and CPU. I too just saw the comparison mentioned above, with the reviewer showing temps for the fan pushing air onto or drawing air from the sink. It showed a 2-4 degree improvement (cooler) with air blowing onto this heatsink (it was an SK-7, just like mine). Can't remember the site either, but if you do a search for SK-7 + review, you should come up with it. You could just try both ways and see which is cooler for your setup...just turn the fan over!

my sig left me for an Honorary Guru...

 

[Guest]

Very interesting. I will have to try that experiment with the PAL8045 in my system now.

 

[Teq]

<b>BUT</b> do it with your finger on the off switch!



---> <b>Press ALT-F4 for IQ test</b><---