Case fan air flow

fire_munki · 10 Mar 2010 at 20:33

About to get another 120mm fan for my system.
This one has a bigger air flow than the single 120mm that came with my case I should think since the case was only 30 odd quid.
The question is do I have the fan that moves the most air as the exaust fan or as the intake at the bottom?

Kurisu Makise · 10 Mar 2010 at 21:52

intake

petriodet · 10 Mar 2010 at 22:01

it should be exhaust and the old one moved to intake no real reason except i think the cpu is more important then the graphics.

VortX · 10 Mar 2010 at 22:11

What you have to consider is...

The intake fan is bringing COLD air to decrease temperatures. An outtake fan takes out HOT air, but doesn't cool anything down. Thus my personal opinion is that an intake fan is more useful.

If all of your fans were outtake fans your temperatures wouldn't decrease that much. If they were all intake fans, they would all be sucking cold air in which would force the temperature inside the case to lower. I'm not suggesting outtake fans aren't needed; of course they are - if you keep pulling cold air in, with no escape for the warm air, the air temperature will gradually stabilise and the intake fans won't do much at all.

If you have the more powerful fan pulling air in you are pulling more cold air inside the case. The outtake fan will pull the remaining hot air out. Even if there isn't a balance in the intake/outtake, the general physics of the air being pulled in will eventually be pushed out.

On another note, hot air rises. So, if you have a case that, intakes through the front and outtakes through the back, put the more powerful, intake fan, at the front. This is because the intake fan is lower - as the cold air is pulled in, warms up, it rises and then exhausts through the slightly higher, outtake fan.

fire_munki · 10 Mar 2010 at 22:16

That's what I thought, just put my hand near the current one and it really doesn't move much air (or so the breeze or lack thereof would imply) so as an intake it would do less than bugger all.
This one is the one I like the look of: Scythe Kaze Jyuni 1900RPM from the store.
It appears to shift the most air. Not that the description states the CFM, had to search google for it. It does appear to be almost double of anything else at just over 100 CFM. Noise isn't an issue as it will be plugged into a fan controller if I want it to drop the noise.

Makhaira · 10 Mar 2010 at 22:32

Airflow doesn't just affect cooling. If you are exhausting more air than you are pulling in to the case, you will create negative pressure in the case, which will drag air in from any gap it can find, including the lower edges of your case, increasing the buildup of dirt and dust.

fire_munki · 10 Mar 2010 at 22:49

Positive pressure it is then.
The scythe a good choice?

fire_munki · 15 Mar 2010 at 19:51

Well I went with the scyth, even with the fan control at the min you can hear it, any one know what resistors you'd need to wire it in to drop it down a bit more? I was thinking a 40ohm one or 50ohm, seems fairly close to the zalman ones but diy is a lot cheaper.
But on the plus side my idle temp is now in the top 20s and prime 95 is in the low 40s, thats a 10 degree drop.
There is also no CPU temp difference between max and min fan rpm but it is at the front towards the bottom so the free air is hitting my HDDs and 8800GT so that must be good too.
I think I should be able to get more out of the E6320 now.