Fan Stacking: Ever heard of it? Your opinions please...

[Brian Frank 0]

It might work well if it's like a turbine engine on a plane, with 1 fan rotating clockwise and the other counterclockwise. This is also with both fans designed to push air the same way, though.

[CUViper 0]

Quote:

NOW, I need some "EE" experience here: Can I reverse the wires on the Stock fan into its motor to make it go in reverse? I know squat about these things... to achieve this "jet turbine" effect??

Yes, reversing the wires on any DC motor should make it spin the other direction. This wouldn't work on an AC motor, because you are just changing the phase, but with a simple DC motor you should be ok. I don't know about the whole jet turbine effect though... after all, I'm ECE, not AE...

[Jerry Atrik 0]

im aware of no jet, turbine or turbo prop motors that turn in different directions. not even in different stages of compression

[Jerry Atrik 0]

2 fans will increase volume of airflow and decrease load on the fans IF

they are the same speed and sync'ed

 

but hey here is an idea

put the fast fan on the bottom and dont plug the top fan in

eventually the dead fan will syn up with the faster one providing the extra airflow

[Jerry Atrik 0]

prolly take about a min to normalize

gotta have plenty of airspace in front of the fans. if the dead fan has to look for air at all it'll start creating a drag on the powered fan.

 

works the same way a gyro does... sorta

[Jerry Atrik 0]

too close, remove the case fan and let the air come as it's needed

the vortex that is created by the case fan will interfere with the "gyro" effect of the dead fan.

i has to be driven 100% by the fan beneath it.☺

[Jerry Atrik 0]

both fans being powered is going to create problems i think

jet engines have all the blades mounted on a single shaft so u know they are turning at the same speed

[ConQueso 0]

A flow of wind high enough to cause significant CPU cooling (beyond that already generated by the CPU fan itself) would likely also cause uneven 'lift' so to say from the CPU fan. Directional air would give the CPU fan's blades going the opposite direction as the wind more lift than the other side, which would lead to excessive wear and tear as the fan would want to spin diagonaly off plane of its mounted axis.

 

If you want better CPU cooling, I'd suggest going with a better CPU fan or heatsink.

[Mr.Guvernment 0]

if they are diff RPM, it will slow it down, cause the air flow will not go at the same speed, u would want all fans with the same speed or rpm's.

 

my little bit

[FrogMaster 0]

Just a couple of hints & thinking ...

- you cannot reverse the wires. There is electronic circuitry in there that will prevent you to do so. You have to physically install the fan upside down.

- the setup could act as a compressor, rising the temp of the air significantly. The compressor stage of a turbine rises dramatically the pressure and the temperature. We have to fog in water or some refrigerent in our big power generation turbine to lower the temperature and rise efficiency (my company builds that kind of - huge, several hundred megawatts - machines).

... but higher pressure air will likely remove more heat from the heatsink - more molecules which can dance the Brownian rock & roll

- I have read a lot of articles about that kind of experiment and I never found somebody noticing a significant improvement. I think good ducting will be more efficient.

- If I were to do this, I would put the slower fan on top and the faster one as second stage, hoping it will be better fed with air. On the other hand the second fan would have to cope with heavy turbulences and its efficiency would drop. That's why we have guidevanes blades in-between each and other compressor stages on our machines. As a workaround,I would put some guide vane device in the air duct.

[FrogMaster 0]

Just consulted a turbine spe[censored]t here.

His recommendation would be to build the setup as follows:

- put a 80 mm fan on top

- put a cone-shaped duct with some cross-shaped guidevane inside the duct

- put a smaller diameter fan below the duct that will blow into the heatsink

- this smaller fan should have a higher cfm than the large one so that it can accelerate the flow.

- in theory you should get higher speed and pressure and some rise in air temperature but overall efficiently would possibly improve.

... and yeah, fog in the air intake 8)

[Bursar 0]

The other thing you need to think about if you reverse the direction of the fan is the shape of the blades.

 

They are designed to spin one way, much like a propeller. Spinning the blades the other way isn't going to do you much good.

 

The other thing that you can do is a twin fan mod where you stick two fans next to each other. This is likely to be much more beneficial.

 

 

Not my piccy - shamelessly borrowed from a website site to illustrate the point.

[FrogMaster 0]

Alec,

those motors are not traditionnal DC motors. There is some electronics inside the hub. When you reverse the polarity, nothing happens. It makes sense as blade profile is designed for best efficieny when rotating one particular way.

Please look closely at Bursar's photo. One of the fan seems to be set upside down. I guess the intention is to have one fan blowing air at the heatsink while the other one sucks air out of it, like having the air flow sweeping the base plate.

[CUViper 0]

Quote:

those motors are not traditionnal DC motors. There is some electronics inside the hub. When you reverse the polarity, nothing happens.

I did say that this would work on a simple DC motor, but I guess I've never tried it on a computer fan before...

[Cynan 0]

Each set of blade on a jet engine are angled differently. If you stack two fans of the same type on top of each other, you won't notice much difference at all.

 

Get a bigger fan that runs at the same speed, or a faster fan of the same size. Thats all you can really do. CPU fans aren't designed to be stacked.