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Question about fans and airflow

Last response: in Components
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December 29, 2011 2:50:32 AM

Hi
So I'm looking into building my first PC and I've stumbled across something that I've found out to be important.
I found out that the general rule of airflow in the case is front/bottom sucking air in and top/back blowing air out.
So now I present you a question; what if the PSU is at the bottom? Do the same principles apply?
Also, how do I know if a fan is sucking air or blowing it? Does it depend on the type of fan? Does it depend on its position or how it's mounted?

More about : question fans airflow

December 29, 2011 4:15:08 AM

you can use a piece of paper to check air flow if you are unsure
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December 30, 2011 2:28:49 AM

I don't fully understand what you guys mean.
@amuffin - Thanks, I read it and found it useful but not very relevant to my question.




This is the case I've selected. Orange outlines indicate where there is a fan that comes with the case (12cm fan). I don't know if it will be blowing or sucking air in. I don't think it'd make sense if it was blowing air out. But if it is, how do I make it suck air in? If I turn the fan around then it will just be blowing air inside, won't it? And do fans that blow air to the front suck air in from the back?
Green outlines indicate where a fan will possibly go, but I don't know because I don't know whether it should go there or near the HDD bays and pointing in that direction. Also don't know if a fan could go there.
I've drawn a diagram to show what I mean. Which way would the fan work?

Diagram 1


Diagram 2


Sorry if this seems stupid and obvious :D 
December 30, 2011 11:14:12 AM

All case fans I've encounter have two arrows raised on one side that indicates the spin direction of the fan blades and then the direction the fan would push air.
December 30, 2011 1:29:41 PM

Both your pictures are wrong man, the way you have the air flowing is backwards, if you look at a fan from that view, it would blow the air away from the viewer 'into the monitor' if that makes sense to you,
the way I describe it is as follows,

You know the four struts supporting the fan? if you have those next to the metal the fan will blow out of the case, if you have them facing into the case it will pull air into the case

and if your psu is bottom mounted, normally there are vents/grill underneath it, this lets the psu suck air into itself then blows it out of the back, so it doesn't affect the cases airflow at all, this is the 'normal' way of things but some people mount them with the fan up, facing into the case theres a whole debate on it as to which is 'right' but if you have the holes at the bottom of the case, use them
hope this clears things?
Moto
December 30, 2011 1:50:03 PM

The motor spider (or motor mounting support) is the exhaust side of the fan, the impeller is the intake side of any standard cooling fan.
December 30, 2011 1:52:27 PM

^Techy version of what I said hehe
Moto
December 30, 2011 10:13:18 PM

Ahh I see. Ok well the case I picked does have a grill at the bottom for the PSU and I picked this PSU http://www.ebuyer.com/190751-be-quiet-530w-pure-power-p....
I also checked amuffin's link and read everyone's posts but a question or two arose. From the pic of the PSU I chose it appears that the fan on the PSU is meant to be pointing upwards, but from the link I got the idea that PSUs are ideally meant to be pointing downwards. Also, for a bottom mount PSU case, does the case need to have room underneath it so air can get sucked in? Or can it just stand on normal ground / table?
December 30, 2011 10:18:52 PM

megas said:
Ahh I see. Ok well the case I picked does have a grill at the bottom for the PSU and I picked this PSU http://www.ebuyer.com/190751-be-quiet-530w-pure-power-p....
I also checked amuffin's link and read everyone's posts but a question or two arose. From the pic of the PSU I chose it appears that the fan on the PSU is meant to be pointing upwards, but from the link I got the idea that PSUs are ideally meant to be pointing downwards. Also, for a bottom mount PSU case, does the case need to have room underneath it so air can get sucked in? Or can it just stand on normal ground / table?

Usually the feet offer enough clearance for a fan-down mounted position. Just don't expect to place it on a rug. It should have a flat hard surface.
December 31, 2011 5:59:42 AM

+1, The unit under my desk is mounted on a couple of blocks of wood just to give clearance for air,
if its just on a desk/ flooring other than carpet you are fine
pics on websites often show the fan on a psu just so you can see what it looks like though
Moto
!