Fan Filters: Blow or Suck?

[vicwang]

I have a foam fan filter directly behind my 80mm case intake fan, so that all incoming air is "blown through" the filter. Would it be preferable to find some way to get it "sucked through" the filter instead? Intuitively, for some reason it would seem like "sucking it through" would be more efficient, without having any evidence one way or another... anyone know for sure?

 

[fatbaby]

SUCKING OBVIOUSLY! You are fscking up your cfm by having them blow...Place the filter infront of the fan and you won't lose as much cfm as you would infront (either way you lose cfm)..

 

[vicwang]

Thanks for the tip, but again, why would this be better? For some reason it would SEEM to be better for the fans to "suck" the air through, but from a scientific standpoint I don't see why it would make any difference. Basically, I'm looking for SOME kind of evidence to back it up one way or another.

 

[tritium4ever]

Frankly there's no difference one way or the other...air is still gonna go through the same amount of filter material so the airflow is identical. However, I suggest that you put the filter in front of the fan so that the dust gets filtered BEFORE it hits the fan.

 

[sodcha0s]

Actually, there is quite a difference. You should always place the filter on the intake side of the fan. (suck) If you put the filter on the exhaust side of the fan, air flow will be diffused and you will not get as good of air movement inside the case.

 

[vicwang]

Thanks for the info, but again, where are you guys getting your information from? I'm not saying you're wrong, just wondering what information you're using to base your decision.

Oh yeah, I would definitely put the filter before the fan *if I could* for the reason tritium4ever mentions, but I've removed all obstructions from the intake fan (cut away all the metal) so there is nothing to prevent the filter from getting sucked in.

 

[Buz2b]

<< Thanks for the info, but again, where are you guys getting your information from? I'm not saying you're wrong, just wondering what information you're using to base your decision. >>

You ask for information and help yet you question that same help. Just a suggestion; don't look the "gift horse" in the mouth. You are not paying for the assistance here. As for a reasonable explanation, putting the filter in front of the fan causes a back flow to the fan. The effect is depleted air flow and ineffecient fan physics. Putting the filter on the intake side causes some minor impedence of the air flow but no interference with the fan itself. The result is better cfm than the other option.


<< Oh yeah, I would definitely put the filter before the fan *if I could* for the reason tritium4ever mentions, but I've removed all obstructions from the intake fan (cut away all the metal) so there is nothing to prevent the filter from getting sucked in. >>

Mount a chrome fan grill on the outside of the fan (just uses the fan frame itself so no trouble here). That will not impede the airflow and will hold the filter media away from the blades.

 

[sodcha0s]

vicwang....

Although I am by no means calling myself an expert, I have a degree in HVAC (heating, ventilation & air conditioning) and worked in the field for almost 10 years. I have a solid understanding of the properties of airflow and heat transfer on a practical level.

Buz2b's explanation is not only very good, it's absolutely correct. And his suggestion about the fan grille will work well, just make sure you get the flat type of grill and all you'll have to do is lay the filter over it, the fan will hold it in place obviously.

 

[LuDaCriS66]

I might not have a formal explanation on why it's better but I have the experience that shows it is. When I first installed a dust filter on my 80mm Sunon 36cfm fan, I didn't know what I was doing and I installed it so that it was blowing air into the filter. That really killed my airflow because with the filter on, I could barely feel any air pushing through. At first I thought it was normal because I was expecting a cfm loss but not that much. So I tried reversing it so that it was sucking air through the filter and it's definately a lot better! The airflow was increased immensly. My case temp went down about 3-4 degrees with the fan sucking air through the filter compared to having it blow through the filter.

So trust me... it's better to have it suck air.

 

[vicwang]

Thanks guys! That tells me everything I was wanting to know... I've now removed the filter, and now I realize just how much "blowback" there was... Before when I put my hand near the fan, it used to feel like it was blowing air OUT, not sucking in. At the time I figured it was the air coming from outside that I was feeling, but now I realize it was the air "bouncing back" off the filter.

I would defnitely try the fan grille, except I'm using an Enlight 7237 case where the intake fan doesn't screw into the chassis and is held in place by a plastic housing that kind of clamps onto the front.... And the way that housing is designed, there is no room to fit a grille or anything in front of the case fan, which is why I had to put it "behind" the fan originally. Place anything in front such as a grille, and it will no longer be possible to clamp it to the case.

Used to be, I could have just put the filter over the metal "cage" that was originally part of the case. But now that I've cut off that cage I don't have that option. I might need to end up drilling holes to mount the intake fan, or I might just go filterless for a while...

Anyway, thanks again for the advice! I think it has definitely made an improvement.

 

[lenjack]

Another important consideration...having the filter on the fan intake makes itmuch easier to clean. No need to open the case. If your're really ambitious, you can put a 120 mm fan on your 7237, with a mesh filter on the outside. It involves a lot of very careful cutting. 2cooltek has the details.

 

[conlan]

You can mount your intake fan with screws on your 7237, just drill a couple of holes. I have a 120mm in the front of mine after some Dremel work. It makes a big difference on the 7237 because of the restrictive front bezel (which also can be modified)