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Fans in series...

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Crazy Jayhawk

Member
Joined
Jul 14, 2001
Location
Hutchinson, KS
This could be something worth checking out. I don't have two fans of the same size in my computer, so I can't really do this.

120 mm fans typically produce a lot of airflow. Now here's the question: If you stuck two of them together end-to-end so the outlet from one went to the inlet of the next, would it help airflow at all? What about noise?

For anyone who tries this out (even with something other than 120mm fans >() I'd greatly appreciate hearing about your findings.
 
W

William

Guest
for a long duct it would certainly increase the airflow although you wouldn't exceed the maximum output for one fan, but over a distance, having one pushing and one pulling will certainly help.
 

lemmingboy

Registered
Joined
Jul 12, 2001
I have tried stacking two of the same fan before, didn't really do anything. Because both fans are rate at the same CFM, the first just feeds the second the air it would pull from the air around it. Basically the second is restricted to the flow that the first puts out.

Something that did work was feeding a high RPM fan with a lower RPM fan feeding it while having an air space between the two fans. The high RPM fan feed off the preaccelerated air and then was able to pull the rest from the air gap. It resulted in less stress on the HRPM fan and a little improvment in air flow and noise, but it wasn't worth implementing into any real situations. I guess the air space thing would work with two of the same fan, but I am telling you its not worth the minimal gain. Plus though it makes sence it may be all in my head, cause I tested by wet finger.
 

Colin

Arctic Silver Senior
Joined
Dec 19, 2000
My temps dropped 3C with a second fan on my Bud Fandapter. Adding a second L1A to the Tee on my Bong Cooler increased the exhaust plume from 6" to 9" above the top of the tower.
 

Luis

Registered
Joined
Jul 15, 2001
Location
Buenos Aires, Argentina
Stacking fans that run in opposite directions can improve pressure (and I think also air flow) in restricted setups (like pushing air through a heatsink). But i´ve heard others say it´s very noisy.
 

cjtune

Member
Joined
Dec 18, 2000
Luis (Jul 23, 2001 02:26 a.m.):
Stacking fans that run in opposite directions can improve pressure (and I think also air flow) in restricted setups (like pushing air through a heatsink). But i´ve heard others say it´s very noisy.

Yup, one of the two fans must counter-rotate. It'll be noisy as the blades constantly pass each other and the compression and expansion of the air because of this is known as blade interference. Good for 'pushing' air through constrictions and impedences in a pathway that would otherwise seriously reduce the airflow of a singular axial fan. Airflow travels 'straighter' as well as the velocity vectors of the airflow from each of the two fans cancels out tangentially.

Oh, BTW, you cannot get DC fans to counter-rotate just by swapping terminal leads. Even so, the fan blades themselves must have been made specifically for counter-rotation.