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Fan - Rad - Fan separation distance ? - Page 2

post #11 of 15
Approximately the radius of the fan should do it. This gives both intake and exhaust fans ample room for "expansion" or "compression" (depending on the fans job). Placing it some distance off of the radiator (or heatsink) can help lower the impact of the "dead zone" - the area of little or no flow due to the hub of the fan.

I have never found a good rule of thumb that pertains to small computer fans, but in my line of work...if we have to close couple the fan to some resistance, we give it some room (usually 1r or 2r)
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post #12 of 15
Interesting. I have seen Cathar post in his work years back 40mm as the ideal gap for a shroud. If you measure the shroud that is provided by Thermochill (made to Cathar's specifications) it is 40mm. That works out to about 1.5"

The shape of the shroud has some effect as well--the ideal shroud has a truncated pyramid shape (like the PA160 shroud).

However for your application that is not feasible.

I think you have a valid question there about the math involved...all I can do is tell you what I have measured and what I have read.

I did find that mounting a fan 90 degrees offset to the rad and using a 45 degree angle in a shroud enclosure to reflect the air into the rad makes for a quieter and apparently still very efficient set up.
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post #13 of 15
Thread Starter 
Here's what I've found so far ...



Found here - http://www.wsdmag.com


A little off topic and yet pertinent to the subject matter ... the only other thing I can verify ( by manufacturer documentation ) is that a similarly designed 120mm fan running at the same RPM but having a depth of 38mm usually, but not always, has greater pressure, less noise, and a higher cfm capability than its 25mm counterpart.

For example - A Sunon fan comparison -



Only a single letter off in model name to designate the 25mm and 38mm difference ... but a good indication of the fan capabilities.

Cathar was saying an approximate 1.75" in the aforementioned post ... but even he was uncertain of this measurement being legitimate.

hmmmm ... some great information and food for thought as well. Thanks everyone !
post #14 of 15
I've found that anything within 2-4mm of the fans actual thickness works best.
one and half inch seems optimum for 38 x 120mm 110-130CFM Deltas/Panaflos.
And center flow dividers tend to do FA for pressure/flow/velocity FME.
  
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post #15 of 15
That 108cfm 120x38mm you left spec's for are on of my favorite rad fan's they pull the same inches of h20 as the 115cfm Pana's my other favorite rad fan.....I'm going to get some 1.5" aluminum channel to make shrouds with and then I can compare it to the 3/4" ones...I still haven't forgot about that test I was going to run for you Joe I have 4 -47cfm Yate Loons here on a shroud waiting to test them first...I still haven't put my shrouds back on my rad yet...I'm lazy Man...
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