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SlyMaelstrom
10-16-2006, 06:00 PM
Hey guys... I'm not all up and up on the science of airflow but I figured someone in this forum would be, so I though I'd ask... which has better airflow: One 120mm fan of 80CFM or two 80mm fans of 40CFM each... or are they both equal? I suspected the two 80mm fans would be better because it's more area, but then I don't know exactly how CFM is calculated, so it may be equal... does anyone know for sure?
STEvil
10-16-2006, 08:47 PM
CFM is a volume measurement of Cubic Feet per Minute of air moved

CFM isnt everything though. You need to know the static air pressure the fan can generate or you'll just get a really fast turning noisy 3 blade fan which does great in a free-air environment but wont do anything with some backpressure happening.

What are you intending to put them on, or where?
SlyMaelstrom
10-16-2006, 09:30 PM
Easy question:

http://images10.newegg.com/NeweggImage/productimage/11-196-021-09.JPG

That back vent allows two 80mm or one 120mm. Keeping in mind that it has a 140mm intake on the front and a 250mm intake on the side... I need good exhaust on the back. So, what do you think would be better? Two 80mm or one 120mm?

This is the case by the way. (http://www.newegg.com/Product/Product.asp?Item=N82E16811196021)
Nanometer
10-16-2006, 09:55 PM
Do you care if it's quiet? Go with a 120mm

I would guess that the 2 8CM fans would make more pressure, so if you don't mind the noise that may be your route.
Navig
10-16-2006, 10:36 PM
Several factors that you must choose from. Sound vs. performance. Pressure performance.

1x120mm fan @ 80cfm is going to be low-medium loud. 2x80mm fans @ 2x40cfm is going to be very loud. If loud is no problem to you, then at the same cfm, the 2x80mm is going to perform better because 80mm fans generate higher pressures.

However, the grill appears to be minimally restrictive, therefore, high pressure is not really needed.

Therefore, I also would recommend a 120mm fan as the best silence to performance ratio. If you want very quiet, I'd recommend a Yate Loon. If you want great performance, medium noise, consider a Panaflo L1.

navig
STEvil
10-16-2006, 10:44 PM
most PSU fans push 35-40cfm free-air. They are not necessarily going to be loud, but a 120mm fan will probably be a better way to go. Cheaper, quieter, and probably identical performance.