140 mm fans aren't that great, most rad fans are 120.
Тhat's exactly it. And the 120mm fans are certainly incomparable when accounting for the cumulative R&D budget.
With that said, 140mm fans have several not- insignificant advantages:
* Due to expansion card and motherboard dimensions (while not using flex-PCI-E solutions) they are a better solution for volumetric efficiency since we already need that dimension. (usually width)
* Speaking of dimensions 140mm fans (hence 140mm rads) have (when calculating crudely) around 35% more surface area. 120mm fans in turn have 26% less surface area. (depending on how you want to look at it)
* Before you argue that more space is wasted in the corners of 140mm fans, I would argue, as a counter..er.. argument that 140mm fans can have the same hub size as 120mm fans so it should be about equalized. Let's do some quick calculations, I have some NF- P12 here so Noctua will be used as an example. The hub diameter is around 40mm and the blade diameter is ~114mm. I don't have a NF- P14 here but the 140mm blades are in the neighbourhood of 130-135mm, I will use 132mm. If we calculate only the disk of the fan blades (assuming the same blade hub) we get around 124cm squared for the 140mm fan and ~89cm squared for 120mm fan which actually favours the 140mm fan with ~39-40% more surface area. (or the 120mm blade having ~28% less)
* I'm no expert but based on what I know the 140mm fans are yet to become as developed as the 120mm. I also see no physics barrier for the proper performance scaling since the 120mm (quality) fan hub can be quite large for the total fan dimension- hence I consider the 140mm as the "sweet spot". Mind you the 180mm and 200mm fans don't scale as well because of the mass increasing rapidly requiring a hub increase, as well as the decreased efficiency at the same thickness, and just some rudimentary reasoning- the atom size and electrostatic force are constant so as we go bigger we get more flex: hence more vibrations and more noise. (and I really,
really dislike noise)
* With all of that said and the general underdeveloped state of the 140mm fan market they still perform
(the good ones as jsco pointed out, though my personal favourite under 1000 RPM are NF-P14S Redux or BeQuiet Silent Wings 2 (120 or 140) in a pressure vs flow vs
noise plot
) as good as 120mm today. (check out the Xtremerigs radiator reviews and crunch some numbers for yourself, and Coolingtechnique and Hardware.fr for fan tests)
I also exclude all ball bearing fans from my selection since they have that whine at any rpm, hence no mention of the legendary GT's, although they scale magically when you can tolerate
some noise (the best really in the 1200+ rpm to my knowledge). Fluid dynamics all the way for
silence.
This is why I design my cases around cooling, and about a year ago when I gathered some knowledge I made the switch from 120mm to 140mm (size permitting of course).
I am not sure if this is considered thread polluting but the mods are welcome to transfer this post where appropriate.