Optimum Shroud Depth?

[PunkRawk911]

Hey everyone, I've kinda been wondering this for a while. If I have a 172mm Comair rotron fan shrouded to pull air through my heatercore, what depth or thickness rather should I make the shroud? I was thinking maybe 1.5 inches, but I was wondering if anyone had any data on how deep your shroud should be for the optimum performance.

[Onlypro]

The farther away, the smaller the deadspot.

Longer is prolly better granted you have the room for it.

1.5"- 6" would be an ideal range IMO.

[wannaoc]

1- 1/2" inch is plenty. But it all depends on the space you have on to what you can use.

[Cathar]

In an engineering sense, and from what a commercial fan engineer has told me, "optimum" is defined as:

1) At least 5 fan diameters
2) No more than a 15° angle for any edge that joins a different sized fan to a different sized radiator.

Having said that, the least distance that you would want is perhaps one half of a full fan diameter.

[omaticrail]

A few people in the forums did some tests with the chevette (IIRC) heatercore and found that after 1" (25mm), a single 120mm fan didn't produce a measurable change in CPU temperature. That's pretty unscientific, and doesn't sound as sexy as Cathar's explanation. It does, however, meet the test of practicality and diminishing returns. Does anyone happen to know what the Chevette core's shroud angle needs to be for a 120mm fan 1" away?

[Sneakytermite]

Hey Cathar, where did you get that info on the optimum shroud depth? Can you give us a link? Thanks man.

[Cathar]

Originally posted by Sneakytermite
Hey Cathar, where did you get that info on the optimum shroud depth? Can you give us a link? Thanks man.

The information was presented by the forum member "Greedy Guido" in the following thread:

http://forums.overclockers.com.au/showthread.php?s=&threadid=123152

He's a professional engineer in ducting and ventilation systems, as well as pumping systems.

He cites "The Chicago Fan Handbook" as the source of his information.