Pondering about Dust Filters and Air Flow

[julienruc]

Hi all,

Here's a thought I've been pondering on ever since I thought about upgrading my loudly inneficient Chinese PC fans.

I own two PC's.
My gaming rig uses a Fractal Design Meshify C Dark TG
My work rig uses a Phanteks Ecplise P300.
Both of which are advertised as fully dust filtered PC cases.

I did notice something about these two cases (as well as other PC cases who advertise as being fully dust filtered/full dust meshes).
Front, Top and Bottom of the cases all have dust filters. However the rear exhaust fan never has one, and there is aslo a fairly sized space with holes at the back, that's usually either next to the rear exhaust fan or next to the PCI-E brackets that's also unfiltered.

So 2 things here.
1. Why does the rear exhaust fan not have a dust filter when the top exhaust does?
2. From a physics standpoint, if the total CFM of your exhaust fans (top + rear) is superior to your total CFM of your intake fans (front), wouldn't the fans naturally draw that extra air from that holed-space next to the PCI-E brackets? In which case it seems to me like a design flaw of these "fully dust filtered" cases. However, I'm certain that these companies' R&D teams must have a reason for this, because what would be the point of filtering everything.

Somebody enlighten me!

 

[Sylvvester]

I use top fans as intake. Intake / exhaust configuration is up to person who builds the system and not everyone follows recommended configuration, but I have never seen anyone using back fan as intake.

 

[Lutfij]

The front and bottom will be places to draw cooler ambient air into the case. The top and rear are points for exhaust. You don't need to filter the exhaust unless you want to study the amount of dust your case throws out with respective case fans.

When you run an aerodynamic test with smoke you'll see that each case behaves differently. The general rule is air will travel from the front to the back in the event there is a fan at the back and at the front and both are the same. I also am an advocate of having both the intake and exhaust fans to be the same spec's wise.

 

[dederedmi5plus]

unless you're at windy desert, most pc cases don't need exhaust dust filter because air (broad along dust) is coming out of rear.

more like how obstructive the internal, the clearer the flow the better intake will prevent dust inserting a pc case, there are PCI slot filter and 120mm or 140mm magnetic filter if you need one

 

[Paperdoc]

Very commonly the designers will have installed at least one more intake fan than the number of exhaust fans, so that under normal circumstances there will always be more intake than exhaust. Thus at small openings (and even the larger one you cite on the back) the air flow will be OUT of the case, preventing dust intake. But if you want to be sure yourself, you need some small source of smoke to trace the air. I've used an incense stick for this. Just move the smoke source near any case openings and watch which way the smoke blows.

 

[julienruc]

Very commonly the designers will have installed at least one more intake fan than the number of exhaust fans, so that under normal circumstances there will always be more intake than exhaust. Thus at small openings (and even the larger one you cite on the back) the air flow will be OUT of the case, preventing dust intake. But if you want to be sure yourself, you need some small source of smoke to trace the air. I've used an incense stick for this. Just move the smoke source near any case openings and watch which way the smoke blows.

Didn't think of the incense idea. I'll give that a go. Cheers

 

[Paperdoc]

Thanks for Best solution.