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fan filters and CFM

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June 4, 2006 10:36:59 PM

Hey,

Does anyone know roughly how much a fan filter brings down the CFM of a fan?

-Kallenin

More about : fan filters cfm

June 4, 2006 11:32:27 PM

Depends on the filter material, from not very much at all to a significant amount, especially if dirty! :lol: 
Regardless, I prefer em...
June 5, 2006 12:09:53 AM

i would say it depends on the filter. mesh would restrict less, depends on how many holes and how small, and something like a cloth filter would restrict more.

any where i would speculate from 1~65%. u cant put how much air flow will be blocked since if the fan onyl pushes 20 cfm a filter would cause it to only push maybe 7 cfm then. depends on the fan and the filter.
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June 5, 2006 12:55:29 AM

Well here's a link to the filter I got:

http://www.cablesunlimited.com/products/Prod_Group.aspx...


It looks like pretty thick stuff. Is there anything I can use to maybe measure air flow? Perhaps I could measure the speed of the air coming right out of the fan with and without the filter to compare. I'd at least get a percentage, since the air flow is proportional to the air speed (and I'm keeping a constant cross-sectional area).

-Kallenin
June 5, 2006 1:53:41 AM

hmm, its foam i would say maybe 40%, i dont think they sell any thign to measure air...
June 5, 2006 2:21:54 AM

Quote:
Well here's a link to the filter I got:

http://www.cablesunlimited.com/products/Prod_Group.aspx...


It looks like pretty thick stuff. Is there anything I can use to maybe measure air flow? Perhaps I could measure the speed of the air coming right out of the fan with and without the filter to compare. I'd at least get a percentage, since the air flow is proportional to the air speed (and I'm keeping a constant cross-sectional area).

-Kallenin




I believe it's made of foam so it shouldn't restrict airflow that much.

I would suggest you clean it once a week to once a month and you should be fine. :-D
June 5, 2006 3:25:35 AM

Quote:
hmm, its foam i would say maybe 40%, i dont think they sell any thign to measure air...


You can buy a device that measures face velocity. I assume fan manufacturers use something like that to rate the CFM of their fans. Not sure of the price but it's probably not cheap. A highly restrictive or clogged filter could easily reduce flow by 50% or more. One common tweak for upping the horsepower on street cars that need air filters is to just double the surface area of the filter. So you can have push out fans and some intake area that's filtered with no fan behind it, but you'd want that filter area to be large to minimize the restriction.
June 5, 2006 3:32:43 AM

Quote:
hmm, its foam i would say maybe 40%, i dont think they sell any thign to measure air...


You can buy a device that measures face velocity. I assume fan manufacturers use something like that to rate the CFM of their fans. Not sure of the price but it's probably not cheap. A highly restrictive or clogged filter could easily reduce flow by 50% or more. One common tweak for upping the horsepower on street cars that need air filters is to just double the surface area of the filter. So you can have push out fans and some intake area that's filtered with no fan behind it, but you'd want that filter area to be large to minimize the restriction.



Indeed, increasing the surface area helps quite a bit! :-D
June 5, 2006 3:58:55 PM

hmm, i got an idea.


make a sort of sandwich. get a filter, then a fan then a filter then if u can another fan.. should keep ur system pretty dust free.
June 5, 2006 4:05:21 PM

Quote:
hmm, i got an idea.


make a sort of sandwich. get a filter, then a fan then a filter then if u can another fan.. should keep ur system pretty dust free.




Great idea :-D

I think I've seen that implemented somewhere but I forget where.
June 5, 2006 4:34:20 PM

Quote:
Hey,

Does anyone know roughly how much a fan filter brings down the CFM of a fan?

-Kallenin


Most exit fan protectors on a PC case block as much as 70% of the fans airflow.

Now that you know that fact...why would you want to put foam in the intake flow to basicly block it further?

Improve the exit air flow (remove the cases exit fan protector) and you will see not just better cooling but less dust inside the case each month when you open it to clean it.

Dust is not so much of an issue as lint,animal hairs and ....cobwebs!

Z
June 5, 2006 5:14:54 PM

Why measure CFM at all? Isn't the temperature what you're worried about? Put the filter in and measure how it affects temp. If the temps are OK who cares about CFM?

Unless of course you're inflating your life raft or perhaps entered in a PC Case CFM league or something.
June 5, 2006 5:45:31 PM

Quote:
Why measure CFM at all? Isn't the temperature what you're worried about? Put the filter in and measure how it affects temp. If the temps are OK who cares about CFM?

Unless of course you're inflating your life raft or perhaps entered in a PC Case CFM league or something.


Obviously, the two are related. I find it logical to consider the tradeoff between excluding dust/lint/hair/food/cats/etc/ and flow. One key issue is that it's not static. Your maximum flow will depend on numerous component like the number/size/speed of fans + inlet area and the factors that restrict those fans and inlets. The internals of the computer matter too, obviously, since they can restrict flow in a big way. The grilles and other fixed issues will determine your optimal flow but things like filters can change their flow characteristics dramatically over time. Some folks just don't remember to do maintenance and/or avoid it like Nintendo-neck. So, bottom line is that measuring the flow quantitatively isn't important to the masses, but if you are considering modifying your filtering, it's not an odd approach to understanding the issues.
June 5, 2006 8:20:53 PM

just put he filter on it. the end. if it restrct air, double up the fans.
June 5, 2006 10:35:24 PM

Quote:
just put he filter on it. the end. if it restrct air, double up the fans.


That's my basic approach and is one reason why I've searched out cases with lots of vent/fan surface.
June 5, 2006 10:42:26 PM

also i think mesh filters are the most useless of all, the holes are too big to help
June 5, 2006 11:01:42 PM

Quote:
also i think mesh filters are the most useless of all, the holes are too big to help


You can find mesh in a variety of sizes. I picked up a bunch of different sizes online and have been piddling with different sandwiches. The fine size stuff is way too restrictive for the fans I'm using. I think case makers are afraid to make mesh filter that load up too quickly, so they make the holes too big. Foam works well and can be cleaned with water, but ozone breaks it down fairly quickly and fans produce ozone.
June 5, 2006 11:16:44 PM

i like cloth filters, best out there.
June 6, 2006 10:49:29 AM

I like fine mesh and foam myself. :-D
June 6, 2006 11:00:18 AM

Quote:
One common tweak for upping the horsepower on street cars that need air filters is to just double the surface area of the filter.
Yeah.....throw a K+N Filter on it. :wink:

PS. that's why i like panty-hose....They are stretchy, so you can vary the

amount of restriction by pulling them tighter, or loosening them off. Elastic

band to hold it tight. :) 
June 6, 2006 1:55:31 PM

lol
June 6, 2006 3:26:34 PM

Quote:
PS. that's why i like panty-hose....They are stretchy, so you can vary the amount of restriction by pulling them tighter, or loosening them off. Elastic band to hold it tight. :) 


Are you talkin' about fan filtration or bondage?
June 6, 2006 3:31:11 PM

Quote:
i like cloth filters, best out there.


Hey, cloth won't hold a candle to my electrostatic precipitator filters. The chicks really dig it when I crank up the power supplies for that bad boy.
June 6, 2006 3:45:29 PM

Quote:
i like cloth filters, best out there.


Hey, cloth won't hold a candle to my electrostatic precipitator filters. The chicks really dig it when I crank up the power supplies for that bad boy.



lol :lol:  :lol: 
June 6, 2006 7:18:03 PM

Quote:
PS. that's why i like panty-hose....They are stretchy, so you can vary the amount of restriction by pulling them tighter, or loosening them off. Elastic band to hold it tight. :) 


Are you talkin' about fan filtration or bondage?Well.....both involve blowing. 8O
!