Radiator (AirFlow) Resistance Article
Overclockers.com: Radiator (AirFlow) Resistance Article
excerpts...
As the radiators' system resistance curves show, it takes a LOT of pressure to get a LOT of airflow through these radiators. Mounting a 92 cfm fan on a radiator does not mean you'll get anywhere near 92 cfm through it - more like 50-60%.
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CONCLUSIONS
One aspect of picking a radiator for a watercooling system is the amount of airflow through it. The "denser" the radiator, the less air gets through. In addition, a radiator with a plenum for the fan is more likely to yield better flow than directly mounting a fan on its fins.
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Main Entry: ple·num
Pronunciation: 'ple-n&m, 'plE-
Function: noun
b : an air-filled space in a structure; especially : one that receives air from a blower for distribution (as in a ventilation system)
Never heard of it.
Nice article though, good link
The fan is elevated slightly off the radiator. In the article, the BE cooling one does not, and the fan will be mounted very close to the fins, while the other two have a slight air gap in between the fan and the fins.
that's what i thought too, until i read the def. from the dictionary and this:
The shroud I use on my watercooled dually effectively acts the very same as the way the plenums on the Swifty and Black Ice radiators do in that it seals the area between the radiator and the fan for more effective airflow and mounts the fan away from the radiator fins for less turbulence, hense better airflow.
Google Glossary has more accurate & thorough explanations than mine:
http://labs.google.com/glossary?q=plenum
Google Glossary is your friend. =)