Case fan air flow

  • Thread starter Thread starter Jon
  • Start date Start date
J

Jon

Which direction should the air flow on a case fan? I have it sucking in
but find no difference in the cpu or case temperature. The manufacturer
(Enermax) indicates it's reversible, but the speed control knob doesn't
appear to be removable. Does anyone else use Enermax?


Jon Cosby
 
Jon said:
Which direction should the air flow on a case fan? I have it sucking in
but find no difference in the cpu or case temperature. The manufacturer
(Enermax) indicates it's reversible, but the speed control knob doesn't
appear to be removable. Does anyone else use Enermax?
Click to expand...

Your PSU unit blows out. If you suck in from the rear, some of the
"fresh" air will be heated air from the PSU. So it's traditional to
suck fresh air in at the front, and push heated air out the back.
 
You blow the air out of the back, and you blow the air in from the
front. If you have a casetop fan position then you blow it out (i.e.
heat rises). If you have a caseside fan position then you can do
either, but I'd suggest blowing it into the case from there.

Yousuf Khan
 
Which direction should the air flow on a case fan? I have it sucking in
but find no difference in the cpu or case temperature. The manufacturer
(Enermax) indicates it's reversible, but the speed control knob doesn't
appear to be removable. Does anyone else use Enermax?
Click to expand...

Here's AMD's current recommendations:
http://www.amd.com/us-en/Processors/TechnicalResources/0,,30_182_869_9460^9516,00.html

Where is your case fan? If in the rear it should definitely exhaust air
from the enclosure - all modern cases have that configuration. In some
you'll see optional intake fans to guide intake air over a video card (from
the side if the case) or to guide over multiple hard disks from th efront
but they do not add to the total volume of air passing through the
enclosure.

Think about it this way: if I have a pipe with a fan at one end moving air
at 16cfm and I add a 2nd fan at the other end of the pipe moving air at the
same speed, in the same direction, is it going to move more air through the
pipe?
 
Bitstring <[email protected]>, from the
wonderful person George Macdonald <fammacd=!SPAM^[email protected]>
said
Think about it this way: if I have a pipe with a fan at one end moving air
at 16cfm and I add a 2nd fan at the other end of the pipe moving air at the
same speed, in the same direction, is it going to move more air through the
pipe?
Click to expand...

Actually yes, but certainly not 2x. The CFM of fans is always quoted
to/from free air, and axial fans are notoriously cr&p at overcoming even
a very small pressure differential, so a 16cfm fan on the end of a long
pipe is going to be struggling to get anywhere close to 16cfm. (I've
burned out several 8" axial fans trying to drive air up 4m of 8" duct,
before I wised up and got the right design for the job).
 
Your PSU unit blows out. If you suck in from the rear, some of the
"fresh" air will be heated air from the PSU. So it's traditional to
suck fresh air in at the front, and push heated air out the back.
Click to expand...

I think this thread bears the question of which fans has the longest MTBF?
It would also be nice to know how dust effects air flow through the
case, we know that a dirty case can have a bad effect on cooling,
depending on the setup. It would be interesting to see some data, which
can help us decide what is the best choice.

Ok I did find this with a quick search, http://www.myri.com/myrinet/FIT/
in that url it mentions that panaflo's MTBF are at 500,000 hours. Another
article mentions the rating at 70,000 hours for their Hydro-wave fans.
Which in my book is about 7.99 24/7 years of use, which is 70,000/24/365
which seems ok, for a normal desktop, but I am sure some servers get more
than that. Of course this does not include the dust, or grunge factor,
which might lower that limit. Does anyone know of any real world tests of
case fan MTBF?

Gnu_Raiz
 
Bitstring <[email protected]>, from the
wonderful person George Macdonald <fammacd=!SPAM^[email protected]>
said


Actually yes, but certainly not 2x. The CFM of fans is always quoted
to/from free air, and axial fans are notoriously cr&p at overcoming even
a very small pressure differential, so a 16cfm fan on the end of a long
pipe is going to be struggling to get anywhere close to 16cfm. (I've
burned out several 8" axial fans trying to drive air up 4m of 8" duct,
before I wised up and got the right design for the job).
Click to expand...

Yeah but a PC case is not a pipe of the same diameter as the fans. In fact
has anybody published numbers on pressure differential inside a PC case?...
hmm, a new product for the overclocker market?:-) I think the bottom line
is: you get more out of running fans in parallel rather than serial, unless
you have that need to guide a significant portion of incoming air towards
some local hot spot.
 
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