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How to measure a fans CFM?

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April 9, 2009 5:46:50 AM

So I'm finally got a silent machine (Sileo 500) but I notice the fans in don't push much air thru. The 2 x120mm fans run about 850RPM. There isn't much to identify them other than the "coolmaster' logo.
I took off the side panel and my case temp dropped about 5 deg Celcius immediately on the internal temp, CPU and GPU.
Is there a way to measure the CFM of my current fans so I know what to get to replace them?

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a c 144 ) Power supply
April 9, 2009 8:15:20 AM

sabathyus said:
So I'm finally got a silent machine (Sileo 500) but I notice the fans in don't push much air thru. The 2 x120mm fans run about 850RPM.


You got what you paid for. Fan noise and air flow, all other things being equal, are directly proportional.
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April 9, 2009 8:36:52 AM

if you want a rough estimate (i love this basic sciences stuff) attach a bin liner to the narrow end of a funnel (make sure you buy a bin liner (refuse sack) that has the capacity on the label) and then place the funnel over your fan exhaust and time how long it takes to fill up. (make sure the bag is empty first, and make sure everything is as sealed as possible..... divide the volume of the bad by the time in mins taken to fill it = flow rate in l/min then convert to cubic feet.
April 9, 2009 8:37:08 AM

if you want a rough estimate (i love this basic sciences stuff) attach a bin liner to the narrow end of a funnel (make sure you buy a bin liner (refuse sack) that has the capacity on the label) and then place the funnel over your fan exhaust and time how long it takes to fill up. (make sure the bag is empty first, and make sure everything is as sealed as possible..... divide the volume of the bad by the time in mins taken to fill it = flow rate in l/min then convert to cubic feet.
April 9, 2009 8:37:20 AM

if you want a rough estimate (i love this basic sciences stuff) attach a bin liner to the narrow end of a funnel (make sure you buy a bin liner (refuse sack) that has the capacity on the label) and then place the funnel over your fan exhaust and time how long it takes to fill up. (make sure the bag is empty first, and make sure everything is as sealed as possible..... divide the volume of the bad by the time in mins taken to fill it = flow rate in l/min then convert to cubic feet.
April 9, 2009 2:33:11 PM

Bin liner??
Your on crack arent you?
God damn computer advice giving crack snorting hippies! be gone with you!

Is the computer running hot? If not does it matter?
As JSC said you wanted a silent computer and you got one, at the cost of airflow.
Increase airflow= increase noise, if its running hot just order some high cfm units to replace them with.

Bin liners dear god, I'm picturing the image in my head of some schoolkid with the lid off his case and mums roll of binbags trying too somehow hold it around the fan housing without losing a finger, TIMMMMMY WHAT ARE YOU DOING WITH MY BLOODY BINBAGS!!!!!!!!!!!!!!! WHY IS THE COMPUTER IN PIECES?? YOU WAIT TO YOUR FATHER GETS HOME!!!!!!!!!!!!!!!!!!!!!

Mwhahahaa classic
April 9, 2009 5:30:49 PM

will_chellam said:
if you want a rough estimate (i love this basic sciences stuff) attach a bin liner to the narrow end of a funnel (make sure you buy a bin liner (refuse sack) that has the capacity on the label) and then place the funnel over your fan exhaust and time how long it takes to fill up. (make sure the bag is empty first, and make sure everything is as sealed as possible..... divide the volume of the bad by the time in mins taken to fill it = flow rate in l/min then convert to cubic feet.


Won't work - the flow rate is quite heavily dependent on backpressure, and that would cause a higher backpressure than the normal operating conditions.
a c 248 ) Power supply
April 9, 2009 7:09:36 PM

I always suspected that with optimal case ventilation, air flow, and cooling plus other effective techniques it would be possible to build a pc using a few 600 rpm fans that would produce temperature/cooling results equal to or at least close to optimal operating temperatures. That's my next project. I am working on the pc case frame right now.
April 9, 2009 7:28:55 PM

It depends on the amount of heat the components are putting out. I suspect you are right, but I don't see a good reason to use 600rpm when a couple of 1200rpm Noctuas are nearly dead silent as it is.
a c 248 ) Power supply
April 9, 2009 7:47:54 PM

cjl - It's more of an experiment. I just want to find out for myself if it can be done. I've done case mods and now I want to try and build a case from scratch.

I read posts in the past where people who installed high volume, high rpm fans throttled them down to 600 rpm. Of course they only did that when they weren't gaming.
April 10, 2009 5:30:36 AM

Thanks guys. That gives me a bit more confidence in buying some new fans.
I was seriously considering the 'experiment' for the fun of it but I can barely feel a breeze off of these so it might take a while to fill the household 20 gallon bags : )
April 10, 2009 5:26:09 PM

case and fan are quite imporant esp that alot of cases only have 1 intake fan in the front but they block it with the hdd rack, when that is the case i'll usually drill holes in the bottom for a 2nd intake fan after the hdd rack. Just use variable fans i got some deathing 3000rpm fans i scale down to 1200 which is slient after an hour or two of 3000 rpm hell 1800 rpm is slient after that.
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