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Originally Posted by gmat
That's figures in open air, not against a backpressure. The rad will create a static pressure that makes the flow drop. The pressure/flow relation is not linear, so without at least mfger data about the fans you're about to use, you won't get any idea.
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How do I find this data? isn't this specification only public with industry targeted fans like Delta, Papst and Panaflo?
The fan is Enermax UC-9FAB.
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Originally Posted by gmat
Also you'll certainly have a drop in performance/noise ratio, as 92mm fans make quite more noise to push as much air as a 120mm.
If you want a powerful & quiet 120mm try the Delta WFB1212M, i've been impressed by this one, it's up there with the best of them if you want quietness, and it flows 72 CFM at 2100rpm...
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120mm @ 2100RPM is definately not quiet in my ears. A Papst 120mm running 1600RPM (55CFM) is driving me insane. I have the Papst 120mm fans and the two Enermax 92mm and the two Enermax 92mm running at 1800RPM is tolerable and moves more air than my Papst 120mm - even with the Papst full speed.
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Originally Posted by gmat
Overcoming "air resistance" is more a factor of the blades geometry, and total surface. Most (if not all) fan motors have quite enough power to rotate at their full rated speed whatever the conditions are.
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I don't know the proper word in English to describe what I mean. If you have a Papst 120mm at 12v and stop the fan with a finger, then when you remove it the fan will immidiately spin to full speed. Having the Papst on 5v og 7v it can barely start again after this action. In my experience it looses power that affects the performance when mounted on a radiator - don't know why, but
I guess it's because of lowered (back?)pressure wich results in worse heattransfer from copper to air.
At that point the Enermax have "full throttle" at all RPM speeds in the variable area.
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Originally Posted by gmat
With proper ducting (large enough shroud) this is not really an issue.
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Any idea of how big? 92 x 40% = ~36,8mm from the radiator core?