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Fan - Rad - Fan separation distance ?

post #1 of 15
Thread Starter 
OK ... I've read scads of discussions about this but have yet to get any concrete numbers for either calculating the proper distance or the best known distance to separate a 120mm fan from a rad.

So, is there a best guess available ?
I've been trying to keep up on this discussion here - cathar's New Test Equipment to see if Cathar gives some solid numbers ... or even a decent formula that can give a person a rough idea.

Another site I've been to stated that even at 9 inches from the fan the air flow is not balanced. The dead space from the center of the fan is still present. Their recommendation was to place a deflection screen after the fan to better distribute the airflow evenly. The problem, obviously, was that while the flow was indeed more evenly distributed, the flow itself was greatly diminished.

Thoughts ? Ideas ?
post #2 of 15
the absolute best option is take a 140mm fan a funnel it down to 120
post #3 of 15
Thread Starter 
Quote:
Originally Posted by bobcool View Post
the absolute best option is take a 140mm fan a funnel it down to 120
If only it were an option ... in my case, I have 16 120mm fans running in a push-pull configuration on 2 GTX 480 rads. Before I place the mounts in the external cabinet, I was hoping to get a better idea of where to place them. If I keep everything internal ... the distance will be around 25mm ( 63/64" ) between each set. If I mount the pulling fans outside of the cabinet, the distance can be opened up to 44.45mm ( 1.75" ) between each. I'm leaning towards the external fan mounting scenario just to give myself a little bit more ... but if there is no measurable difference, I'd rather keep everything inside the cabinet for sake of aesthetics.
post #4 of 15
About an inch is all you need, any more than two inches you will start losing pressure.
post #5 of 15
Thread Starter 
Quote:
Originally Posted by RyGuy View Post
About an inch is all you need, any more than two inches you will start losing pressure.
Is there a site with calculations or a formula I can use to verify?

I'm not doubting you, I just like to "do the math" as it were.
Call me old fashioned.
post #6 of 15
That's just what I've heard from all the WC pros around here, and just from my own logic/what all the pre-made shrouds are like. I will see if I can find anything for you though.
post #7 of 15
Thread Starter 
Much appreciated !

Yup yup ... I've read anywhere from 1" to 1.75 inches for optimal distance ... but no numbers to verify it. Could be different for 140mm fans compared to 120's ... can't say.
post #8 of 15
I don't know Joe if you find out let us know....I've always heard around an inch and a half but thats just hear-say...Let us know if you find out for sure...


I've tried to keep up with his fan testing but it gets to be pretty dry reading......
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post #9 of 15
I think it probably depends a little on the fan type. A small hubbed consumer styel fan with a little hub probably can do better with less than something like a commercial grade panflo. The hub size on the commercial 38mm fans is probably twice the radius.

1.5" has been what I've heard also.
    
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post #10 of 15
I couldn't find anything in the way of reasoning. I think the hub idea is good, the bigger the "air gap" the wider the shroud. I would make a square between the "gap" and the rad, so if the fan motor hub is 1" wide, make a 1" gap, and if it's 1.5" wide make a 1.5" gap. Makes sense to me.
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