double fans better then single??

J

jwill

2[H]4U
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wierd question but just entertain me if you have any idea...

would stacking two 80mm fans improve/decrease/remain the same air flow cfm as a single 80mm fan?

would it matter either way, i mean ive got an extra which is why i thought about it.

getting tired of this 92mm tornado, even at 3000 rpms. :rolleyes:

edit: exact same fans stacked.
 
It would decrease airflow. Unless the fans were exactly synced, the top fan would be blowing onto the bottom one, but the air would hit the blades on the bottom one, causing turbulance and reducing airflow. Likewise, the bottom fan would be trying to suck through the top one, but its blades would restrict it. You would just end up with a loud mess that didn't push as much air.
 
forgot to add they would be the exact same fan. (coolermaster 80mm LED series)
 
depends

If you're pushing air through a high-resistance device, like say, a heater-core, then two fans are almost definately better than one. IF you're pushing air through a radiator though, it would probably work better to have one fan on one side and one fan on the other side.

Turbulant airflow accross a heatsink is better than laminar airflow though, so if adding a fan will increase flow a bit, and increase turbulance, then it will improve performance.
 
should have added the application theyd be used for...

slk-900a

edit: ill just try both ways and report back my results.
 
current temps with the slk-900a and 92mm tornado @ 3000 rpm using as3. using a probe next to cpu core. overclocked, 210x11, 1.9vcore.
idle temp taken after 30 minutes with no appications running. load temp taken after 30 minutes playing enemy territory.

ambient: 21c
idle: 32.5c
load: 41c

gonna try single fan next, then double...
 
2 fans stacked are crap. I tried it with 2 antec fans, exact models, and there was like a 70% decreas in CFM.
You can just overclock your fan....increase the voltage, but shortens life. Or do some stupid mod like I did. I glued a metal disc on the fan, it caused it to spin a bit faster and when powered down it spun longer before stopping.
 
increasing weight of the fan impeller will not increase the rpm of the fan, just give it more momentum, and make it spin longer
 
ok, switched fans. also note the decrease in overclock.

temps with the slk-900a and a single 80mm cooler master led fan @ 2300 rpm using as3. using a probe next to cpu core. overclocked, 200x11, 1.75vcore.
idle temp taken after 30 minutes with no appications running. load temp taken after 30 minutes playing enemy territory.

ambient: 21c
idle: 33.5c
load: 43c

double next...
 
temps with the slk-900a and stacked (2) 80mm cooler master led fan @ 2300 rpm using as3. using a probe next to cpu core. overclocked,

200x11, 1.75vcore.
idle temp taken after 30 minutes with no appications running. load temp taken after 30 minutes playing enemy territory.

ambient: 21c
idle: 32.5c
load: 42c

i knew the temps wouldnt have much difference if any. ill probably just have one instead of 2 stacked.
 
Originally posted by t0x1k
2 fans stacked are crap. I tried it with 2 antec fans, exact models, and there was like a 70% decreas in CFM.
You can just overclock your fan....increase the voltage, but shortens life. Or do some stupid mod like I did. I glued a metal disc on the fan, it caused it to spin a bit faster and when powered down it spun longer before stopping.
Click to expand...

no....you just thought it was spinning faster because it was louder and off balance.

btw...as for stacking fans im not sure, but if you have a fan behind another fan it will sping faster. Guaranteed. Even stacked fans should increase airflow.
 
It depends on the design of the fans. I have two identical 92mm server fans, and when stacked, they have about the same airflow. They also tend to, er, be a HELL of a lot louder than they would be running in single. I did get an increased airflow, though.

The only real and useful benefit of having two fans in this configuration is to legthen the life of the fans (if they have good bearing design). Unless you get signifiganly reduced airflow, the fans should be spinning faster, thus having less draw (or something like that, not exactly sure what).

This tends to work for larger fans.

Take an electrical fan. Alone, it can push air up to say, 7 mph. Put 7 mph wind going into said fan... Now, the fan will be moving the air at 9 mph. If the fan has poorly designed bearings, it will wear out faster, though.
 
Stacking identical fans results in increased airpressure, but won't affect airflow (although it might reduce it).

The theory behind it is that both fans work together to push the same air, meaning that each fan has to do less work. It won't magically spin faster, however.

Anyway, only thing to keep in mind is that the air leaving a fan is very turbulent, so it's a good idea to reduce the turbulence before it goes through the second fan. I've been told that a mirrored, non-spinning fan (or similar) can be used for this.
 
Originally posted by Elledan
...

Anyway, only thing to keep in mind is that the air leaving a fan is very turbulent, so it's a good idea to reduce the turbulence before it goes through the second fan. I've been told that a mirrored, non-spinning fan (or similar) can be used for this.
Click to expand...
like the tornadoes have right?

by the way, i do not miss my tornado. i can accually hear my hard drives working and keyboard sounds. :p
i feel much more relaxed at the computer now. :)

ive got a new goal now... make it silent.
 
Originally posted by Spewn
Turbulant airflow accross a heatsink is better than laminar airflow though, so if adding a fan will increase flow a bit, and increase turbulance, then it will improve performance.
Click to expand...
Not sure where this idea comes from, as it goes against my understanding of basic fluid theory. Turbulent flow (as opposed to laminar) has a negative effect on heat transfer, since there is no steady flow of fluid (air in this case) passing over the surface of the heatsink. The turbulence instead causes the air to tend to pass through the channels without removing heat.
 
Originally posted by jmcmike
Not sure where this idea comes from, as it goes against my understanding of basic fluid theory. Turbulent flow (as opposed to laminar) has a negative effect on heat transfer, since there is no steady flow of fluid (air in this case) passing over the surface of the heatsink. The turbulence instead causes the air to tend to pass through the channels without removing heat.
Click to expand...

Nope, you are wrong. :)

If you have laminar flow, only a small volume of the air passing over the heatsink comes into direct contact with it. (Only the boundary layer.) Since air is a good insulator, it will actually insulate the rest of the air from the heatsink, thus minimizing airflow. If you have a turbulent boundary layer, much more of the air will come into direct contact with the surface of the heatsink, thus vastly improving heat transfer.

..namely, the presence of small eddies that mix hotter fluid with colder fluid at a rate much higher than could be accomplished by molecular collisions alone. ..
Click to expand...

http://www.mas.ncl.ac.uk/~sbrooks/book/nish.mit.edu/2006/Textbook/Nodes/chap13/node17.html

I've also got my heat treanfer book sitting here next to me, and I could look up the relevant equations if you are so interested. :p
 
Originally posted by defcom_1
Nope, you are wrong. :)

If you have laminar flow, only a small volume of the air passing over the heatsink comes into direct contact with it. (Only the boundary layer.) Since air is a good insulator, it will actually insulate the rest of the air from the heatsink, thus minimizing airflow. If you have a turbulent boundary layer, much more of the air will come into direct contact with the surface of the heatsink, thus vastly improving heat transfer.



http://www.mas.ncl.ac.uk/~sbrooks/book/nish.mit.edu/2006/Textbook/Nodes/chap13/node17.html

I've also got my heat treanfer book sitting here next to me, and I could look up the relevant equations if you are so interested. :p
Click to expand...

exactly right. what's your text? we use incropera and dewitt
 
Originally posted by Elledan
Stacking identical fans results in increased airpressure, but won't affect airflow (although it might reduce it).

The theory behind it is that both fans work together to push the same air, meaning that each fan has to do less work. It won't magically spin faster, however.

Anyway, only thing to keep in mind is that the air leaving a fan is very turbulent, so it's a good idea to reduce the turbulence before it goes through the second fan. I've been told that a mirrored, non-spinning fan (or similar) can be used for this.
Click to expand...

Interesting. Instead of arguing, I'm going to hook up some 5,000 rpm 120mm fans and see how many RPM they do, then put them together and see the difference, between one running alone and two stacked.
 
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