Static Pressure vs CFM rating

[Tiamat]

I have been reading around and it seems that "static pressure" is an important rating to consider when picking out fans. Is higher static pressure better for cooling a cpu? a system? What if there is a lower cfm but higher static pressure?

I have an enermax 92mm variable fan on my SLK947U right now, would a panaflo 12L cool the processor better even though it has less cfm, but potentially higher static pressure? unfortunately the enermax doesnt have static pressure listed on its stats.

Is static pressure kinda like "the concentration of cfm rating per area"?

thx

 

[AnnoyedGrunt]

Static pressure is the differnce between the airpressure on the input side of the fan and the air pressure on the output side of the fan (so essentially it indicates the amount of resistance the fan must push against). You will see in most fan flow curves for aixal fans (the type computers use) that only a very small amount of pressure differential will really lower the flow rate of the fan. When the fan makers put out a single static pressure number I'm not exactly sure what they mean. Hopefully they mean the static pressure @ which their advertized flow rate was measured, but you never know unless you can find a fan flow chart.

Check out the pdf on this page for an example of the flow chart. You can see that as the static pressure increases, the flow drops drastically, until it stops altogether. At this point the fan is just cavitating and unable to push the air against the pressure.

http://www.nidec.com/ta300dc20/ta300dc20.htm

Also, they specifically note that their CFM ratings are based on zero static pressure. This is one reason why people often advocate setting up a "balanced" flow in your case, since often the fans will operate much more efficiently when you have a similar amount blowing in as you do blowing out. Setting up all your fans to suck air out or blow air in the case will create a pressure differential that the fans will have to work against. OTOH, you now have all your fans contributing to the flow, instead of just half of them.

Anyhow, hopefully that helps a bit.

-D'oh!

 

[0roo0roo]

yup. case fans have very little static pressure. so getting them to force air through shoddy cases with those tiny holes at the fan mounts and bezels in the way etc is horrible. to get anywhere near that free air "cfm" rating u need to obstruct as little as possible.

old but still good read http://www.dansdata.com/hx45fan.htm

read fans 101 on the side.

 

[Tiamat]

Sorry guys, im still kinda befuddled.

Lets narrow it down to "I already have balanced CFM in and out"

Im looking for a very effective but very quiet cpu 92mm fan.

The panaflo M series 92mm fan seems to be the "recommended". I noticed it had a 48cfm and 3mmH20 rating.

My enermax 92mm fan spinning at 2000rpm probably puts out similar cfm rating, however the max air pressure reading is nonexistant.

I take it that max air pressure is different than static air pressure. If this is the case, does max air pressure refer to the pressure imbalance the fan can take before not functioning?

Does this then further imply that it would be beneficial to have some sort of direct intake from the left side panel to relieve any pressure differential?


Also, somewhat unrelated, why does my 80mm12L exhaust feel like its pushing out a higher concentration of air than my other so-called higher cfm/higher noise 80mm fans?

thx

 

[0roo0roo]

don't worry about it. case fans are so weak any pressure differential is nothing to worry about. they cant really change the pressure in your case. unless your matching tornados to voltage modded l1a's or something, it makes no difference. if your hardcore, get a sheet of plexi, stick to side of case so u can see inside. then bring out a fog machine and watch your airflow.