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Push/Pull fan config theory

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December 16, 2010 1:57:26 PM

[planning a wc loop with only internal rads]

Understanding that it most likely won't matter much but purely for the sake of optimization:

most people seem to use the same fans on each side of a push/pull config and I'm not sure why.
The way I understand it in a push/pull configuration the pushing fans need a high static pressure to deal with the resistance posed by the radiator. So in my mind since the pulling fans don't have a rad to push through, so shouldn't they just need a high CFM rating and static pressure won't matter much?

so if I wanted to optimize my push/pull setup with about 80mm of fan thickness allowed, which is better: 55mm thick triebwerks pushing and some high cfm 25mm fan pulling or 38mm thickness fans push/pull?

basically is there any reason I am missing that a pulling fan needs a high static pressure?
a b K Overclocking
December 16, 2010 2:48:27 PM

In fluid dynamics, pulling air creates laminar flow and pushing creates turbulent flow.
"In laminar air, different streams don't mix so heat stays localized more. Opposite with turbulent air. also turbulent air is more likely to "hug" the fins of the heatsink, so they tend to have better conduction of heat properties.

Base on this(note; depends on the type of fan/rad), you should always try push first and then pull. However if you are doing both, then I guess it doesn't matter"
"with about 80mm of fan thickness allowed"..hmmm??,i don't think they sell 80mm thick fans,but if you can find one of this ...get your self some good headphones :) 
what type of radiators are you talking about?
http://martin.skinneelabs.com/Radiator-Fan-Orientation-...
December 16, 2010 4:00:33 PM

for rads I have been flip flopping btw xspc rx240 and black ice sr1 240

by ~80mm of fan thickness space, i meant total to width of pushing+pulling fan

I am also giving alot of consideration to noise and based on martins fan vids I really liked the 38mm ~1350rpm (low speed) yate loons. But then I was also really impressed by the sound of the medium speed triebwerks

was worried that 55mm fans in push/pull might not fit in the case and was hoping I could get away with 25mm fans rated ~88cfm pulling (triebwerks peak cfm rating) with the triebwerks pushing, without wasting the potential of the triebwerks. Also thought I could save some money by using pull fans that don't have high static pressure.

The fluid dynamics angle is still a bit over my head I'm not sure what to conclude from that, article was a great read though! I was surprised that you only get a 20-30% performance gain by going push/pull over a single fan. If I am understanding correctly though he attributes the gainin performance to the increased pressure caused by adding another fan. It seems likely that if I get 2 triebwerks I should have them pushing. I suppose what I am wondering now is do you only experience that pressure gain while adding a fan of equal or greater static pressure rating, if that makes sense.

edit: the only properties of fans I have considered to this point are cfm and static pressure rating, this could be erroneous.
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a b K Overclocking
December 16, 2010 5:20:47 PM
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Both xspc rx240 and black ice sr1 240 are great Rad's( both have low FPI-fins per inch),SR1 have shroud on one side and is limited by it, and how you mount that Rad
Here is thread on 120MM rad fans ,it will help you to pick up the right fans for the set up;
http://www.xtremesystems.org/forums/showthread.php?t=26...
http://skinneelabs.com/triplesv2.html
Both of this rad's are optimized for slow to medium fans," It seems likely that if I get 2 triebwerks I should have them pushing"..no, slow moving(800~1400rpm) fans perform best in shroud/pull conf.,pull/push will improve overall performance but the gain will be minimal
The best thing you could do for any type of RAD'd is the supply of fresh/outside of the case air
P.S. it's always easier when you post the specs/case..of the system in question
December 16, 2010 9:13:49 PM

Best answer selected by Littleyo.
a b K Overclocking
December 17, 2010 1:05:08 PM

Exhaust is much more important than intake. As long as there's holes for intake, you really don't need intake fans. The exhaust fan's will passively pull in all the air they need.
Imo, intake is really only good for blowing on certain components such as video cards.
!