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gmat · 12-28-2005, 08:54 AM

I mean, the matbe graphs do not reflect the static pressure vs airflow equation. They did only indirect measurements (by the means of temperatures) and with 1 static pressure situation that certainly won't match yours.
Now half the work is done by the fan mfger who provides (generally) PDF's of fan specs with static pressure vs airflow graphs (at least i know Delta, Panaflo and Papst do it). You'll see it's far from linear (a bit like pumps, really).
The problem is, guessing the static pressure created by a given rad. Generally you can assume thicker = more pressure, but fin spacing and construction have some influence. There's a thread currently in these forums about that precisely (testing real airflow of 120mm's on some rads).
Also the shroud has an effect, and the closeness of the fan relative to the rad... Think about tip vortices interacting with stuff around. If you have 2 fans you'll want to isolate them so their respective vortices don't interact. You get the idea, more turbulence = more noise.
What i ended up doing (for lack of data) was getting as many 120mm's as i could and testing them with my real setup (i already had a rad, though)

12-28-2005, 08:54 AM	#9
gmat Thermophile Join Date: Mar 2001 Location: France Posts: 1,221	Re: How to choose the optimal 120mm fan? I mean, the matbe graphs do not reflect the static pressure vs airflow equation. They did only indirect measurements (by the means of temperatures) and with 1 static pressure situation that certainly won't match yours. Now half the work is done by the fan mfger who provides (generally) PDF's of fan specs with static pressure vs airflow graphs (at least i know Delta, Panaflo and Papst do it). You'll see it's far from linear (a bit like pumps, really). The problem is, guessing the static pressure created by a given rad. Generally you can assume thicker = more pressure, but fin spacing and construction have some influence. There's a thread currently in these forums about that precisely (testing real airflow of 120mm's on some rads). Also the shroud has an effect, and the closeness of the fan relative to the rad... Think about tip vortices interacting with stuff around. If you have 2 fans you'll want to isolate them so their respective vortices don't interact. You get the idea, more turbulence = more noise. What i ended up doing (for lack of data) was getting as many 120mm's as i could and testing them with my real setup (i already had a rad, though)