2x 80mm fans on one CPU. I wonder...

[Rednut05]

So I have wondered this the last week or so and opened up a thread asking if anyone had done this. Turns out no-one really had but 'PieEater' shared my wondering thoughts and I put it on my 'To Do' list and I ahve been doing it tonight.


Okay so the question being; does 2x 80mm CPU fans pull their pants down over 1x 80mm CPU fan?


My specs are as follows;

AMD64 3500+ running at 2.2GHz Stock.
2 GB RAM (4x 512mb).
6800GT 256mb clocked toooo….oh I don’t know. (Stock cooling)
550W PSU.

So Cooling wise in my computer I have;

1x 120mm rear exhaust fan.
1x 120mm PSU fan (looks 120mm to me).
1x 80mm CPU fan (stock AMD fan and heat sink).
1x PCI exhaust fan (seems to me a bit of a pointless buy but hey).


So basically I was wondering on cheap ways to cool down my computer. And I came across the idea of putting a spare 80mm fan on top of the CPU 80mm fan I already have running…..But I lost my spare 80mm fan so I’m taking one from the family computer for this purpose.


So loading up Everest I can tell you currently my CPU is running at 30 Degrees under no load and spinning at a 3184 RPM. I have MS Word, MSN, Everest and Firefox running so as I said no load.


So now if I plug in the spare 80mm fan to my CHA2_FAN socket it spins nicely as wanted. Now I have taped the other fan onto of the current one at its started spinning.

So now before mod: 30 Degrees – 3184 RPM
Initial (1/ 2 minutes): 32 Degrees – 2909 RPM
5 minutes: 34 Degrees – 3375 RPM
10 minutes: 34 Degrees – 3668 RPM

Conclusion: No gain, just the most annoying noise of the air cutting between the two fans. Temps went up ~4 Degrees and fan ~484 RPM.


So that was the fan the default way round…hmm I wonder what happens when I swap it around the other way!?

So put the other fan back on and the original fans spin rate.

So now before mod: 30 Degrees – 3182 RPM
Initial (1/ 2 minutes): 30 Degrees – 3516
5 minutes: 29 Degrees – 3516RPM
10 minutes: 29 Degrees – 3514RPM

Conclusion: There is not much more noise produced than the original single fan, but a louder noise none the less. I guess it could be explained like the noise 2 fans spinning instead of one
So after about 10 minutes it’s still hovering around 29/30 Degrees and a stable 3516 RPM from the fan so nothing really to report here.

 

[Rednut05]

Now ‘PieEater’ wondered what may happen if there was a gap in-between that is still sealed up, so basically a gap between the fans.

Now this should be a fun bodge. Now this would be a lot easier with glue but this spare fan has to be back on the family computer by the morning! So hmm…

15 minutes later….

Its modded (fan correct way round), about 20mm gap though and it’s taped up with lecky tape as wondered.

So now before mod: 30 Degrees – 3125 RPM
Initial (1/ 2 minutes): 32 Degrees – 3265 RPM
5 minutes: 34 Degrees – 3560 RPM
10 minutes: 35/ 36 Degrees – 4018 RPM

Conclusion: A sealed gap does nothing inbetween. I would do it with an open gap inbetween, but not tonight as I’m knacked. 6 Degrees temp rise and 893 RPM increase. Hmm wooohoo to that.


So basicly…one 80 fan is better than two on top of each other. But how about both blowing from the side of the heatsink?, or one on top and one on the side?

For another day.

 

[w3bbo]

Two fans so close together would do nothing except increase noise (as you have found). The reason for this is that the the air passing through the first fan is the same amount that would be passed through the second fan and therby no increase in volume (CFL).Having one fan with a greater CFL than the other defeats the object as one fan can only use as much air as its being fed.

One fan blowing and one fan exhausting should result in a cooler heatsink as the air is being pushed/pulled through the heatsink more efficiently but bear in mind that air cooling can only cool as far as the ambient temperature lets it i.e the warmer the 'fresh' air coming into the case the warmer the cpu will be. Heatsink effeciency also has a part to play. Air will inevitably warm up as it collects heat from the mothboard/GPU/ so it is already heated before it reaches your CPU which is why some people like to use a duct or a side case fan feeding fresh air to the HSF.

GL in your testing