Fan size

[paul mohr]

I am having a brain fart here and wondering which moves more air? Given the choice between a 80 mm fan that moves 80cfm and a 120 mm that moves 40ish which is actually better? Do you gain any advantage by have more area or is 80 cfm 80 cfm regardless of the size?

And if that is the case, what is the point of even making a 120 mm fan at 40 cfm? just to hog up more space?

Paul

 

[SpidersWeb]

higher CFM = more air flow.

The CFM rating is the measurement of how much air it flows in total.

The idea behind bigger fans also is not always to do with more flow, its normally to do with the fact they spin slower to produce the same air flow as a smaller fan. 120mm fan doing 40cfm will be much quieter than an 80mm fan doing 40cfm because the blades will be spinning much slower.

But if you have two fans, identical design, both spinning at the same rpm, but one is 80mm and one is 120mm, the 120mm model will flow considerably more air.

There are other factors (such as bearing design and balance) that effect noise as well.

Why make a 120mm fan with only 40cfm? Well not only is it going to be quieter, but also I've found you often don't need fans pushing lots of flow. My case came with 7 fans standard, as a result I run all of them at 40-60% of their capacity, so the need for low flow quiet fans are definately out there! Most of my fans run at around 800-1000rpm (at 100% they do 2000rpm mostly, but the extra cooling is barely noticeable and the noise is!)

 

[paul mohr]

Makes perfect sense SpidersWeb. Larger diameter equals more flow for less rpm, which equals less noise due to less air disruption at the blade tips. Told you it was a brain fart lol.

I can see a few more advantages for larger fan as well now that I think about it. For one if you were using on a large heat sink or radiator the larger fan would cool more area which would mean more heat dissipation. And if you were using the larger fan for an exhaust it would cover a larger area and probably be better at removing the hot air.

Not to mention the larger fan would not only be more quiet, it would use less power.

Thanks for your help and kicking my brain back into working again lol.

Paul