would two fans on top of each other cause tubulence?

[iLoveDivX]

i was planning on stacking my small cpu fan on top of the radeon 9700 fan. would the two fans blowing in cause turbulence or more airflow?

 

[Research]

turbulence is good ... that's what it would cool it better. Don't worry, your components are secured well enough .. so as not to be blown away.

 

[Vegito]

thats what I heard.. better off with 1 better fan/sink...

good luck

 

[mindless1]

It'll cause MUCH MUCH turbulence... a whole lot of extra noise but not so much better airflow.

For that card I'd go all out... get a nice 1U copper or Cu/Al heatsink and size/shape-mod it if necessary. Tap mounting holes and/or arctic alumina epoxy it to the lapped GPU. Put a good 60 x 15mm x 3K RPM fan on it.

 

[iLoveDivX]

by turbulence, i mean the air cancelling each other out. like a dead zone type of thing where air doesn't flow. i know the fan won't come off...sorry for the misunderstanding

 

[onelin]

I probably wouldn't on a videocard, even if it'd be ok. I have doubled up 80mm intake fans in my case, though I've been told even that may be a bad thing. (next time around I'll just find space for two that aren't stacked for more airflow)

mindless1's idea sounds good

 

[pelikan]

Originally posted by: onelin0
I probably wouldn't on a videocard, even if it'd be ok. I have doubled up 80mm intake fans in my case, though I've been told even that may be a bad thing. (next time around I'll just find space for two that aren't stacked for more airflow)

mindless1's idea sounds good

I have two intakes stacked for intake too, but they are on either side of a plastic cube that separates them by four inches or so, like a square wind tunnel. I get very very good airflow from these.
With your's stacked right on top of each other can you feel them giving more air flow than a single fan? I'm thinking of stacking an extra one on my exhaust.

 

[dkozloski]

What you need between the fans is a stator to straighten the airflow like the axial flow compressor in a turbine jet engine. Next best would be countra-rotating fans.

 

[iLoveDivX]

so if i don't have a tunnel type of thing, should i go ahead and stack them? i can't test them to see the airflow cause the fans are connected to the gpu.

 

[silent tone]

I read a long discussion on this before, and the conclusion was that it does create a lot of turbulence. Mounting fans in parallel (if possible) is much more efficient.

I never took a course in fluid mechanics, so they could've been making it all up.

 

[onelin]

Originally posted by: pelikan

Originally posted by: onelin0
I probably wouldn't on a videocard, even if it'd be ok. I have doubled up 80mm intake fans in my case, though I've been told even that may be a bad thing. (next time around I'll just find space for two that aren't stacked for more airflow)

mindless1's idea sounds good

I have two intakes stacked for intake too, but they are on either side of a plastic cube that separates them by four inches or so, like a square wind tunnel. I get very very good airflow from these.
With your's stacked right on top of each other can you feel them giving more air flow than a single fan? I'm thinking of stacking an extra one on my exhaust.

It's how I originally did it, so honestly I'm not sure. After reading more on it, I kind of question how much it helps. I was just following a case mod I saw here in the anandtech forums a couple years back. I have a filter over the intake, so I guess even a small benefit would be good.

I'm no expert on airflow, but I think you want some kind of pressure pushing the hot air out of your case (i.e. more intake than exhaust) ...so I wouldn't bother with a doubled up exhaust...instead if you don't have one I'd try adding an exhaust on the top of your case. (I have 3 intakes, 2 exhaust + PSU fan)

 

[mindless1]

All stock video card coolers are junk compared to any old socket 7 heastink on a nice lapped GPU. Runner up to a good socket 7 'sink would be a specialty GPU cooler. Of course I'm ignoring water-cooling...

Since you're not considering either of these alternatives I'm assuming you want to keep the original cooler on for warranty purposes. In that case I'd just remove the original fan, it's more likely to impede airflow than help (assuming a good alternate fan).

 

[mindless1]

Doubled-up intake or exhaust fans only create more airflow when there's a large pressure change, a system that's very well sealed or has an abundance of intake or exhaust but no place to put fans to balance the airflow. If possible you're usually better off adding a second (alternate location, not "doubled") fan or larger fan. Higher RPM would work too but who wants a noisey 'pooter?

 

[MadRat]

If you double them up then the bottom one will not work as hard. Since the bottom fan will be just barely out of sync (slightly less resistance boosts its velocity over the top fan) it will hardly be more turbulent than normal. The top fan will actually work less hard too because the backflow will be minimal. Logic would say that BOTH fans would last longer than a regular fan but that may not be the case since both fans will be spinning faster than their design was intended.

If you want "superflow" then it would be better to use two stages rather than just two fans; the bottom fan should rotate faster than the top fan. If you want smooth airflow then you need the bottom fan to rotate the opposite of the top fan. Just remember, the fans weren't designed for these purposes so they may fail faster using them out of the norm.

 

[thorin]

No stacking two fans won't help. However if you can fashion a little bracket that will hold the CPU fan and attach under one of your slot screws and blow across the other HSF (across the video card) to help displace the heat coming off the card (both top and bottom) that'd help.

Even better would be to have it suck towards the side of your case, where you mod your side panel with a few strategically drilled holes and make a side vent to suck the heat out. (You could even setup a little bit of ducting to direct the air flow).

Thorin

 

[0roo0roo]

dansdata.com has a nice article on this. think its in his mains fan mod article.

2 fans on top of each other will basically have more power to resist obstructions to airflow. it won't increase or double the airflow at all. you will at most have the same flow as the max of the slowest fan.

so if u have a case with sH*t ass airflow and poor ass ventilation a doubled fan might be needed to force air around.

otherwise 2 separate fans would basically move twice the amount of air compared to a stacked fan.

 

[Lalakai]

I would be concerned about the fans potentially "stealing" from each other and giving you a lessenend cooling effect. You would have more impact by adding a slot cooler next to the card, or by possibly adding a large exhaust fan ontop of your case. bottom line, wouldn't do it myself.

edit = spelling

 

[MadRat]

Originally posted by: 0roo0roo

otherwise 2 separate fans would basically move twice the amount of air compared to a stacked fan.

Barring added resistance from backflow pressure that is.

 

[0roo0roo]

yup, gotta have intake and exhaust fans.