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Fan direction?

Last response: in Overclocking
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December 8, 2001 2:45:36 PM

I have three case fans, 4 counting the cpu fan. My first is the usual case fan at the front which is pulling air in, and then I have a fan in the back sucking air out. My last fan is mounted on the side of the case. Will it cool better if it's pulling air in, or blowing air out?

More about : fan direction

December 8, 2001 4:16:17 PM

I'd suggest having it blow in.

Martin, Michigan (girlfriend's house)
December 8, 2001 4:47:10 PM

I second that for blowing in. It'd cool your CPU/PCI cards more, since the air from the front fan isn't getting that far. I wish I could setup another fan on the side... :eek: 

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December 8, 2001 8:51:50 PM

yeah..i third the direction of BLOWING IN, because that will also give you more of a positive pressure in the case, which is better than having a vacuum because heatsinks rely on air to work, and if there is a vacuum, then it will cause the heatsinks not to have as much air flowing across them...
and yeah, a fan on the side of the case, even when that is the only fan you have mounted in your case, it is going to cool your computer well...like pretty well.
at least it does for me.
the only fans in my case are as follows:
80mm power supply fan...blowing out...

40 or 60..not sure...cpu fan....blowing down on the heatsink.

120mm fan on the side cooling the expansion cards and the cpu, partially.

overall system temps dropped 2 or 3 degrees C after putting the 120mm in...
and the cpu temps dropped by 4 or 5 degrees C....
so it really helps to add a case fan or two!

-DAvid

-Live, Learn, then build your own computer!-
December 9, 2001 9:59:35 AM

Let it blow in! One of my intake fans is on the side of my case, just above the RAM mem. My CPU temps is 37 C, case temp is 26 C

My case has so many fans that it hovers above the ground :eek:  .
December 10, 2001 8:33:33 AM

Suck!(if you use Alpha PAL 6035 or 8045)
:p 
(and blow for most other brands/models)
December 10, 2001 8:34:35 AM

why suck?

-DAvid

-Live, Learn, then build your own computer!-
December 10, 2001 4:16:13 PM

Because Alpha recommends your CPU fan to be mounted blowing air up (from the bottom of the HS to the top).
It could be that he means that it will suck the heat out of the case with the casefan. Or he didn't read the post right and thought it was about a CPU fan.
I myself have an Alpha PAL6035 and I let my side casefan blow in.

My case has so many fans that it hovers above the ground :eek:  .
December 10, 2001 7:41:02 PM

ah, it makes sense now...
but i dont know how much that will help the cpu fan, because you will still creat a vacuum in the case, and since the heatsink's fan needs air to draw across the fins, you would want air coming in...sure, not RIGHT above the fan on the heatsink, but somewhere, otherwise you would be hindering the heatsinks performance. right?

-DAvid

-Live, Learn, then build your own computer!-
December 10, 2001 9:00:04 PM

I installed my alpha 8045, with it set to suck, my temps were about 41c idle. I set it to blow and my temps idle are 37c. I am using a sunon 3000rpm, 50cfm.
December 10, 2001 9:16:11 PM

hmm....odd...
wonder why they want you to set it to pull th air through...maybe it is quieter?
i dunno

-DAvid

-Live, Learn, then build your own computer!-
December 11, 2001 12:56:49 AM

The Alpha PAL 8045 HSF setup is best utilized when the fan is expelling air through the heat sink. AKA blowing onto the HS instead of drawing air onto the HS and then going through the fan. In laymen's terms ... Air go through fan onto fins good...air through fins and then through fan bad. <A HREF="http://www.micforg.co.jp/c_pal8045e.html" target="_new"> See here for proof. </A>

Now about the case airflow... Neither positive pressure or negative pressure will really do anything. Now I know for all of you physics and mechanical engineers out there will agree. Low pressure as stated before is bad because there is less air molecules colliding with the HS thus transferring less energy from it. However the other is true in the fact that with higher pressure there is higher latent energy and remember Pivnert and moles form chemistry?(PV=NRT) High pressure in a given space increases temperature given all things remain the same.

Enough of all of that useless info...

Keep the airflow as even as possible. There are a lot of other posts with examples of stuff you can do to decrease your case temp. If you want some for your edification on this thread just ask and you shall receive.

Good luck!

<b>All for one and one for all...and 3 for 5! - Curly - The Three Stooges</b> :lol: 
December 11, 2001 1:55:58 AM

i need some help about air flow...please refer to the "60mm to 80mm fan adapter funnel"...please help...thanks!

I try to smile everyday but I can't... :smile:
December 11, 2001 2:25:14 AM

ok, i was just wondering why people were saying to set the fan to pull the air through..
i thought that it was better to have the fan blowing down on it.
and as far as the pressure, i dont think that you are going to be able to create a high enough pressure to actually raise the temps....it is much easier to remove enough pressure out of the case to raise temps tho...i have dont that.
i have never raised the pressure enough to make the tmep go up...only down.
you would need to construct your case like a compressor to make it buid up enough pressure to outweigh the ammount of cool air being pushed into the case.
it is best to have it even...but then you need to direct the airflow...by sealing holes, and putting two identical fans, one blowing in, and one blowing out..(ideally bottom front in, top back out)
if you dont seal up the holes in the case, then the air will escape, and the air pressure will be more negative.
think about it...
lets say you have a 120mm fan in the front.
and a 120mm fan on the back.
but there are holes all over the place where air pressure is leaking out...and in, but you also have that 120mm fan pulling air out...it would not be that much, but to get the optimal air circulation, you would want to seal up holes. and remove the pre-fabbed holes that they put on the back of the case. and use one of those grills, or nothing at all, just watch out for the blades.
and for the front, the same thing...as little resistance as possible.

but i think that i would rather have a higher pressure in my case, since that has been what i had the best cooling performance with.
maybe you have had better results with negative pressure...but i have had better performance with positive.
also, i havent sealed up my case..i just have the 120mm fan bringing the air in on the side, and my psu fan pulling the hot air out the back.
seems to work for me, since my computer never hits a system temp over 30*C...
and my room can get pretty warm.
right now...it is at 28*C...but i am not doing much...you know...winamp, IE explorer, the usual things running.
yeah, i remember all that stuff from chemistry class, but it doesnt really apply unless you have a real high pressure in your case, which is pretty much impossible with the way case fans are made.
they arent like a sealed impellar or a piston that you would use on a compressor...

-DAvid

-Live, Learn, then build your own computer!-
!