Fans on the OUTSIDE

SlaveToSilence · Post by **SlaveToSilence** » Fri Jan 16, 2009 1:24 pm

if a fan was mounted on the outside instead of the inside of the case (im thinking of a fan with the grill cut out) wouldnt it increase airflow a little as it all rushes to the back rather than some of it lost around the side of the fan etc would certainly be a smoother route for the air
it might also make it quieter, depending on the setup, as the noise of the fan wouldnt be resinating around the case as much?
just a thought

what do you all think?

Forester · Post by **Forester** » Sat Jan 17, 2009 4:40 am

Not sure if the increase in airflow or reduction of noise will be significant if there are originally no major obstacles in the pathway of the air through the fan, or the space between the fan and the case is small enough so that little air is circulated back into the case. But installing a fan outside certainly helps in a cramped case if there are components very near the fan.

I have made two inside to outside modifications in the past. The first one was an old HEC PSU that had bulky components inside almost touching the fan. After moving the fan outside, I could feel the airflow at any given voltage (I also built an external voltage adjustment for the fan) was higher because there was more free space around the intake of the fan.

Another mod was a case fan that I felt was too close to the CPU cooler so I moved the fan outside. The effect on airflow was again positive.

Both modifications decreased the fan noise but most of that decrease was probably due to softmounting the fans. But I'm sure that relieving the negative backpressure certainly didn't do any harm.

SlaveToSilence · Post by **SlaveToSilence** » Sat Jan 17, 2009 5:21 am

Made a little diagram to show what i was thinking, #1 & #2 showing that having the fan on the inside would either create a small deadzone around it where the air barely moves, or have it coming back around the edge causing turbulence and again reducing airflow whereas in #3 the air would/should move much for freely?

Vicotnik · Post by **Vicotnik** » Sat Jan 17, 2009 8:35 am

At the low airflow inside a computer chassis the effect would be minimal I think. Perhaps it's relevant in other implementations such as aircraft engines or whatever, but when it comes to computers the esthetics have higher priority for most people I think. Fans on the outside are ugly.

SlaveToSilence · Post by **SlaveToSilence** » Sat Jan 17, 2009 8:40 am

there is also the possible flaw that having the fan outside would mean it would have to be slowed down to acheive the same noise level, illiminating any possible improvement to airflow

rowan123 · Post by **rowan123** » Wed Jan 21, 2009 11:53 pm

i have tried it when i needed to make room for a big heatsink. makes no difference to performance, just doesnt look as nice. airflow will go in the easiest route from an area of more pressure to less. the vortex on the side of the fan you have drawn will be very minimal/non existant.

Post by **NeilBlanchard** » Thu Jan 22, 2009 3:10 am

Hi,
The problem that this can address is tight clearances, as was already mentioned. If the space around the fan is obstructed, then this definitely affect the noise level, and moving the fan outside creates an additional inch of space; which can be critical.

DrCR · Post by **DrCR** » Sat Jan 24, 2009 8:56 pm

As mentioned by others, it's really only useful for when you are trying to mod a case to a better layout.

Pics here of a late ninetys-era case modded into the 120mm era. Currently sporting a fan-modded EarthWatts and 500rpm Slipstream. Ugly, yes, but great props at lan parties.