Air pressure / fan speed

[zagood]

Interesting...I'm doing some different fan configuration tests, just messing around, and noticed something when getting my baselines.

I opened up Speedfan, which unfortunately only reads my CPU fan speed, to get some temps. I recorded the CPU fan speed (789 rpm) and temps with the side on. Took the side off, walked away for a half hour to let it stabilize. I returned to find (as I knew I would) lower chip temps and higher MB temp, but I wasn't ready to accept the difference in fan speed - 812rpm, a +23rpm difference between the side of the case being open or closed.

I put the side back on, and a few seconds later Speedfan registered 789rpm again. Took it off, 812rpm. This was immediately verifiable, there's no bizarre alien influence doing this.

So, fanmeisters...why?

btw - TRUE 120 + SlipStream 120mm 2100rpm on a Sunbeam Rheobus.

I'll be testing some other scenarios as well just for gits and shiggles.

-z

 

[Ika]

To be simple, with the side panel off, the fan has an easier time pulling air from outside the case through the fan. With the side panel on, the enclosed space means its harder for the fan to draw outside air in.

The same thing happens to my own Yate Loon fans - I think I get something like a 50 RPM difference when I put the fan filter + grill on the front of my case on or off.

 

[Bluefront]

Yeah....sounds like your case is excessively negative pressure, with too little intake area. You remove the case side and the pressure is more neutral.

To fix.....cut some more intake holes at strategic locations, or add another intake fan, or raise the rpm of the existing intake fans(if any). The Slip-Stream fans handle airflow resistance better than most fans, so I don't think a fan change would do much. But if there's no other symptoms, not much to worry about.

 

[DerwenArtos12]

Originally posted by: Bluefront
Yeah....sounds like your case is excessively negative pressure, with too little intake area. You remove the case side and the pressure is more neutral.

To fix.....cut some more intake holes at strategic locations, or add another intake fan, or raise the rpm of the existing intake fans(if any). The Slip-Stream fans handle airflow resistance better than most fans, so I don't think a fan change would do much. But if there's no other symptoms, not much to worry about.

NEG, slipstreams are pretty bad at handling airflow resistance, the Sflex are quite good but the slipstreams are below average, obviously depending on the ammount of restriction.

 

[Bluefront]

FWIW......I spent a bunch of time actually measuring different fans and their ability to handle airflow resistance. Both the S-Flex and the Slip-Stream tested similarly in their ability. I have seen many theories in this area, but few real tests. My own tests might be somewhat different from the others (if you can find any), but I'm convinced of the validity of the results.

Fan testing against airflow resistance.

 

[DerwenArtos12]

Originally posted by: Bluefront
FWIW......I spent a bunch of time actually measuring different fans and their ability to handle airflow resistance. Both the S-Flex and the Slip-Stream tested similarly in their ability. I have seen many theories in this area, but few real tests. My own tests might be somewhat different from the others (if you can find any), but I'm convinced of the validity of the results.

Fan testing against airflow resistance.

With a LARGE foam filter like that I would be surprised if any quality fan dipped more than 10% which is pretty close to the manufacturers acceptable deviation. No offense to your system or your test method but, by restriction I mean a thinner fan sized filter, heatsink or radiator. Good to know they respond well to low restriction though.