120mm counter-rotating matched pairs?

[bradsm87]

Anyone know of any fans that have an identical twin butrotates the other way and obviously the fan blades inverted?

Just imagine how efficient and quiet a twin 120mm (25 thick each) with 5 blades each instead of 7 each would be! with normal 120mm's, it needs 7 to get enough "grip" with the air. Having another counter-rotating fan behind it gives each one more "grip" and they also cancel out each other's radial force (pushing air around and around instead of out) and all of the power of the fans is used to push the air OUT!

You would need them about 25mm apart as not to have heaps of turbulence between the blades. Damn that would be awesome and i I guarantee it would be quieter.

So anyone know of any???

 

[zip22]

counter rotating fans have been talked about and Mr B used one in a northbridge cooler. they increase the pressure, but not the flow. the only ones i could find where the ones Mr. B used and they're made by JMC i think. they only come in 40x50mm and 40x40mm and are loud. over 30db if i remember correctly.

some 38mm thick 120mm fans have 5 blades:
http://www.sidewindercomputers.com/ystech120mm.html

also, have a look at some of these beasts. seem to incorporate the idea kindof:
http://www.sidewindercomputers.com/delffb1212eh.html

 

[stan03]

the delta isn't counter-rotating, but yea it is a beast

 

[zip22]

yeah i know, but the do the fins on the top of the fan help to concentrate the flow?

 

[stan03]

i think thats the bottom of the fan ... hmmm it might but i can't say for sure. it would make sense since the fins seem to be faceing the opposite direction of rotation...

arch where you at???

 

[Ven0m]

This delta has very nice air-directing fins...
Fan rotating in opposite direction would do similiar job, but just better.
Nice idea, worth concerning; problem might be finding nice fan going in that opposite direction. As for first fan, delta won't be nice cause of these fins. That second fan will also limit rotary movement of air - nicer pressure.

So basically I see 2 problems:
- finding & matching 2nd fan
- difference of speed of blades will be huge, and they will work 1-by-1; if 1st fan gives too high rotary speed to air, such setup would be hella noisy.