conter rotating fans

[adamtekh]

any one know of any fans that dont turn clock wise?

[Crazy Jayhawk]

Originally posted by adamtekh
any one know of any fans that dont turn clock wise? Which side of the fan are you looking at? If I turn my fan around backwards it looks like the blades are turning the other way. :p

[adamtekh]

ok i got this idea from some airplanes ( i used to be big air plane buff wantred to become pilot and all that ) well any ways

they use conter rotating props for high altitude

i was just thinking this would give me some good cfm in a smal package

just for a test i took 2 simaler cheap 2 $ 60 mm fans stacked them and got some really good air flow close to high end 80 mm fans

stacking them makes more noise than haveing them horisontel

i wanted to test if haveing both pushing air but one turning right , and the other left ( just like them air planes )

excuse the bad spelling as i am 16 and i dont do to well in english class , but get a+ in every computer class i take

[Crazy Jayhawk]

What I mean is this - let's suppose I have two fans that turn the same direction. One of them is pointed toward me, the other away. One will appear to turn clockwise, the other opposite.

Which way do the blades turn when you look at the outlet side (typically has a few plastic bars to hold the motor)?

[adamtekh]

i hope this answers your question

[Paul -The Mad Hatter]

you could mod the fans by removing the fins and putting the the other way, then flip it upside down and voila you have the fan spinnig in the opisite direction. someone I belive wrote an article on attzaching some fins to a fan, I'll go find it for you and then go to bed.

[adamtekh]

u speak as if that kind of moding would be easy

[Paul -The Mad Hatter]

Originally posted by adamtekh
u speak as if that kind of moding would be easy

yeah I know, it was just one of those suggestions you just throw out there.
couldn't find the article.

[adamtekh]

thanks for trying

[Über~PhLuBB]

Have you tried just reversing the wire's polarity? Negative to positive, positive to negative.

The fan blades are designed to push more air when spinning clockwise, but if you reversed the polarity, you could make the blased spin counterclockwise, but it wouldn't be as effective.

By having 2 fans back to back like that, the fan turning clockwise (utilizing the shape of it's blades) would create more airflow than the reversed one, which would create a minor ammount of drag on the counterclockwise-turning fan.

To solve this, just turn down the voltage on the clockwise-turning fan, to make it less efficient, and this, making it just as efficient as the counterclockwise turning fan, removing drag.

There was an article about a week ago that explained how to get 7 volts from a Molex connector. Try looking around for that one. (I know you connect the red wire to one lead, and the yellow wire to another lead, but I don't remember what's positive or negative. Now that I think about it, I don't suppose that would matter with a fan...)



This should give you the effect you're looking for.

[cjtune]

Some boring theory:

Axial fans, by virtue of costruction, tend to blow air outwards at an angle and with a swirl rather than straight ahead. This is, in a way, bad a most of the air is not focused in the direction in which it is needed and hence is 'wasted'. There are two ways to correct this:

1.) By stacking A counter rotating fan (ie. two fans only) that pushes in the the same direction. This way, the swirl component of the airflow velocity will cancel out and they will travel 'straighter' plus some extra airflow. This gives better pressures/head. (Pressure is energy per unit volume and head is energy per unit mass).

2.) But fitting a tube and vanes at either/both the intake and exhaust of the axial fan. These additional components help straighten the airflow as well and is common for industrial fans.

Notice that the 50cfm 60mm deltas have vanes at the front... The vanes are at an angle due to the short length of the vane portion. Vanes used are normally long, and straight.

[adamtekh]

interesting stuff!!

would reversing the wire's polarity doi any damage to the fan?

[Kingslayer]

Reversing the polarity rarely works and can damage some fans.

Counter rotating propellors on planes are used at high altitudes because the air is too thin to keep the plane up to lift speed. That is why they are used.

They are used in marine outdrives because it negates the left or right drift of the outdrive due to the twist of the props. That and they eat seaweed like its nothing.

Down here on Earth, the air is thick. It's not necessary to have counter rotating fans. You will move the exact amount of air as one fan. (If they are the same fan only counter-rotating.)

Take the marine outboard for instance. The speed and acceleration of the boat are determined by the pitch of the propellor. (Much like the ring and pinion gear in automotive axle's). Let's say you have a 16:1 pitch prop. That means that that propellor will move forward 16 inches everytime that it rotates once. If you put two counter-rotating props on the same out drive, you won't get 32:1 because you have two props. You still get 16:1.

The same holds true for fans. If you get two 32CFM counter rotating fans you will get 32CFM not 64. You will get a quiter setup with reduced vibration, but there are cheaper and easier ways of accomplishing this.

[adamtekh]

well i get more air flow with 2 fans stacked non conter, and yes it is loud

[Kingslayer]

There is not much to be gained by stacking fans that rotate the same. Due to the turbulance created it can't push twice the air, and yes it is loud.

It's both cheaper and easier to just go buy a bigger fan. CFM-wise anyways.

[adamtekh]

i dunno about cheaper cuase i can get these 60 mm fans at 2 $ a pice , and isnt turbulance a good thing for case cooling?

[LimeyGreg]

Look on the body of the fan, there are two arrows that show rotation and air flow directions. NMB model 3110NL-04W-B50 rotates ccw when looking into the exhaust side of the fan, all the other fans I have rotate cw.

I tried stacking this 80mm fan with another 80mm and the noise is quite a bit more than a single fan. The output is higher, but I doubt it is twice the CFM, I don't have a way to measure the cfm - maybe a cheap annemomter would work. What two counter-rotating fans will provide is greater static pressure and if used in a ducted delivery system should provide a better airflow than a single fan or even a pair of fans stacked that rotate in the same direction.

Hope that helps.

[adamtekh]

so what would about 6 fans every other one turning diferntly ?

would this create a turbin or something of the sort?

[adamtekh]

i went to nmb website and couldnt find any thing on "NMB model 3110NL-04W-B50"

[cjtune]

Originally posted by adamtekh
so what would about 6 fans every other one turning diferntly ?

would this create a turbin or something of the sort?

For axial fans, two is practically the max. After the air comes out from the second fan, it has nearly no swirl left so adding a third fan ruins that. You can combine vanes with counter-rotating fans. (Gas) turbines have multiple stages so to extract the energy from hot gasses with better efficiency. Compressers also have multiple stages but the blades aren't that of axial fans but centrifugal impellers.

[adamtekh]

so about 6 high speed delta fans should to the trick then eh?

[J0hnnyBrav0]

Originally posted by adamtekh
so about 6 high speed delta fans should to the trick then eh?

LOL!!! Hell no. 2 fans stacked will give you maybe 1-5 CFM more.
All the second fan would really do is ADD heat to the air the first fan was blowing. Plus because of the turbulance the first fan makes, the second fan will be constantly buffeted and the RPM will go up and down a lot. (adding to even more heat as the motor tries to compensate) if you already have 2 fans the best thing you could do is place them both side-by-side on your heatsink.

What REALLY determines the output of ducted fans (every computer fan you see is ducted) is the diameter of the fan and the power of the motor. Another factor in DF efficiency is the pitch of the blades and the LENGTH of the duct.

All computer application fans have the pitch/diameter of the fan properly designed for the power and potential RPM the motor produces....

SOOO the only way to produce a more efficient airflow rating is this:
#1: Larger diameter fan (most effective solution)
#2: make the intake of your little fan larger (with your fan attached to your heatsink or case, make a little cardboard or plastic cylinder the same diameter of your fan securely attached to the open (intake) side of your fan.

[adamtekh]

u seam to be mistaken becuase this blows cold AIR and gives me way more than +5 CFMs, oh and to fix a typoe these r 80 mm fans im useing

[adamtekh]

ok let me tell u how i have this setp

on the botom its a 80 mm sleve bearing with 4 motor holders

on top its a 80mm ball bearing with 3 motor holders

i dont know if that means any thing to u

[cjtune]

The reason, I think, that two stacked fans with the same direction of rotation output more cfm is that the DC motor in the axial fans we use tries to use up a const. amount of power every time. The air after coming out of the first fan already has swirl to it, ie. it has a component of velocity moving WITH the rotation of the fan blades. So when it reaches the second fan, the second fan must spin much faster (to maintain const. power) because the air it intakes is no longer from rest and worse of all, the air moves in the same direction of its spin (swirl). The fan spins faster to play 'catch-up' but most of the power will go into fighting the resistance from the bearing and not into pushing the air. The air coming out of these two stacked fans will still have a swirl component (aggraviated) and will not lead to a higher pressure-producing capability.

[adamtekh]

well it cools my video card realll nice , and voodoo 3 3000 run hot stock and ive got this thing from 166 to almost 200

i ahvent updated my signature latley i am now at 560 mhz

5 * 112 this gives me a 37 mhz PCI clk to :)

and im at 197 on the voodoo 3 3000

[cjtune]

Originally posted by adamtekh
well it cools my video card realll nice , and voodoo 3 3000 run hot stock and ive got this thing from 166 to almost 200

i ahvent updated my signature latley i am now at 560 mhz

5 * 112 this gives me a 37 mhz PCI clk to :)

and im at 197 on the voodoo 3 3000

Well, no problem then. But I do not recommend stacking fans together in series as they give little (but still noticeable) improvement in airflow and may wear out the second (exhaust) fan faster as it has to spin harder. Why not put two fans side-by-side (in parallel)? It's definitely give 2x time output of just one fan but unfortunately it will be distributed over the coverage of both fans and not concentrated over one hotspot as you might want it to.

[YMAN]

What about changing the second fan to a delta fan?

[adamtekh]

i have no delta fan to test :(

[Über~PhLuBB]

I found the following article. This should clear alot up for you, adam.

http://www.overclockers.com/tips336/

[cjtune]

Originally posted by YMAN
What about changing the second fan to a delta fan?

The two fans must be (counter) spinning at the same speed to be able to cancel out each other's swirl to get straight airflow. Besides the stronger fan will find the weaker fan to be an obstruction.

[adamtekh]

Lots of good feedback! Fan stacking can work under the right circumstances but don't look for double the airflow - theoretically impossible. I did find some benefit, but minimal CPU cooling impact. Also

I stacked a Delta 4700 RPM fan on top of a SANYO 5100RPM fan and got an effective reading of 6400RPMs on the bottom SANYO from the mobo header (KT7, using VIA Monitor and MBProbe). It also lowered my highest fully loaded temps by 4C from 51C on a Athlon 1200 @ FSB+10 to 47C (MBProbe).



Quick point: Any company that sells coolers with stacked fans doesn't enclose the space between them, for example the old Step Thermodynamics coolers [ED NOTE: Not quite so - some do]. They weren't like one duct, with a fan at the bottom and fan at top. They used one fan, then another separated from it. Try that. I placed a fan on top of my Gorb and dropped the temp; then I got an FOP38 and SERIOUSLY dropped it.

The ONLY way you get a performance boost of 20% or so is if the second fan is rotating in the OPPOSITE DIRECTION to the first


yes thank u for finding that

and i never was looking for twice the air flow any ways

[Oright]

Heres what Ive done to get the most out of my fans (dont do this if you want to use these for a long time, they wear out pretty quickly after this.......);
all the fans on my baybus are running at 14 volts, and although this isnt a huge increase on the 12v from a psu, it DOES make a very noticable difference!
Just take out any adaptors that you can adjust the voltage with and viola..... more effective than using 2 fans.......
I cant be bothered to figure this out right now, but you can hook up all the fans on 14v to turn on with your psu......
hm.....;)

[adamtekh]

i dont feal like OCing my fans

[cjtune]

14V seems acceptable. The lousiest fan I had lasted me 3 yrs -it was spinning really slowly due to wear but at least it's still spinning....and that was a no-name fan. Even if your fan lasts 2 yrs after the voltage increase, it's still a pretty good way to squeeze out some more cfm. But the main prob will be to get the 14V in the first place instead and you gotta do some circuitry if you don't wanna buy those expensive rheostat busses.