Another quick fan question...determined to get really quiet setup...

[night_2004]

I'm thinking about replacing my heatsink fan, but need some idea of how many CFMs I need in order to get the job done.

My heatsink (Dark Knight S1283V) comes with a 120mm fan that outputs almost 90CFM at full blast, or 2200RPM. 99% of the time my fan is running at only 20%, which is great as I do not really hear the fan at those speeds as other noise drowns them out. At least right now I cannot hear the fan below 50% and that gives me enough cooling capability that my CPU barely touches 70C at full load with IBT.

But I've got some new parts coming in (quieter 140mm fan, almost silent PSU) and I expect that either the GPU fans or CPU fans will become the loudest component in the system. So the next thing on my "how to silence" list might be to swap out the CPU fan. Can't do much about the GPU fans without going to custom cooling (no thanks for now).

The 120mm case fans I use I literally cannot hear beyond a few inches away from the case (44CFM, < 20dBA). So I was thinking about putting two of them in a push-pull setup on the heatsink and running them full bore. Or maybe just one, depending on what kind of airflow I get.

So here's the question...does the CFM output roughly scale linearly with the fan speed?

 

[BillParrish]

No, CFM output directly scales linearly with fan speed. (haha could not resist, yes you are correct.)

CFM2 = CFM1 (RPM2 / RPM1)

The link below is very informative and while we can never get the numbers we need for precise calculations the overall concepts and an understanding of how the variables interact with each other make this a must read for serious fan nuts. ( I just put a big over engineered honker on there and turn it down with a control, but I am lazy).

http://www.comairrotron.com/airflow_note.shtml

Careful, not sure how your last question relates to your using push pull so did not address it. The link has insights to multiple fans.

 

[Mr. K6]

The secret to getting great temps with low noise on a heatsink is to use a high pressure fan. The cooling potential doesn't directly come from the CFM output of the fan, but how much air it can actually push through the fins of the heatsink. Most fans are rated in open space, and based on their design (fin shape, type, number, speed, etc.), their air-moving properties can change drastically when pushed up against a heatsink. I've always been a fan (lol) of using 120x38mm fans on 120mm heatsinks. Being 50% thicker than your standard 120x25mm case fan, they produce much more pressure and therefore can be run at lower speeds and noise. You can also check out fans with different designs. I've seen Scythe's Gentle Typhoon model recommended many times for radiators and heatsinks because of its low noise/high pressure properties (I haven't used one myself though, so I can't comment further).

Also, if you're trying to isolate noise sources in your case, check out your hard drives. Many whine just like fans and are a pain to get quiet.

 

[SicKlown42012]

The GentleTyphoons are great. I've used plenty of fans for heatsinks and they've been the best as for cooling ability/noise. The 1850rpms are quieter than most 1600rpm case fans.

 

[night_2004]

No, CFM output directly scales linearly with fan speed. (haha could not resist, yes you are correct.)

CFM2 = CFM1 (RPM2 / RPM1)

The link below is very informative and while we can never get the numbers we need for precise calculations the overall concepts and an understanding of how the variables interact with each other make this a must read for serious fan nuts. ( I just put a big over engineered honker on there and turn it down with a control, but I am lazy).

http://www.comairrotron.com/airflow_note.shtml

Careful, not sure how your last question relates to your using push pull so did not address it. The link has insights to multiple fans.

Thanks. So assuming the pressure of this other fan I'm looking into is enough (not sure) then it might be something worth trying. I've already got a spare fan or two of it so it isn't like I'll spend more money trying it out.

As far as push-pull goes, if my understanding is correct using two fans will double the fan pressure without increasing CFMs. So it's more likely that particular fan setup will achieve its rated CFM when blowing through a heatsink or vent.

The secret to getting great temps with low noise on a heatsink is to use a high pressure fan. The cooling potential doesn't directly come from the CFM output of the fan, but how much air it can actually push through the fins of the heatsink. Most fans are rated in open space, and based on their design (fin shape, type, number, speed, etc.), their air-moving properties can change drastically when pushed up against a heatsink. I've always been a fan (lol) of using 120x38mm fans on 120mm heatsinks. Being 50% thicker than your standard 120x25mm case fan, they produce much more pressure and therefore can be run at lower speeds and noise. You can also check out fans with different designs. I've seen Scythe's Gentle Typhoon model recommended many times for radiators and heatsinks because of its low noise/high pressure properties (I haven't used one myself though, so I can't comment further).

Also, if you're trying to isolate noise sources in your case, check out your hard drives. Many whine just like fans and are a pain to get quiet.

I noticed a few 38mm fans over at FrozenCPU, was not sure if they were worth looking into or not. I guess it comes down to their mmH2O ratings...

Let me guess, air pressure ratings are also roughly linear with respect to fan speed? EDIT...looks like it is not linear but a squared relationship.

I am still trying to find more of Xigmatek's rubber fan mounts though, and if I go with a push-pull setup either the fans need to be quiet enough that I can run them at full blast all the time....or I find a way to hook two fans up to my single 4 pin CPU fan header and make sure I am not going to overload the circuit. Call me lazy but I do not really feel like swapping out the heatsink yet...I might have to take it off again a month from now on cross country move for the summer so I will change the heatsink then only if I have to then.

As for hard drive noise, I'm already using two SSDs for my OS drive. My mechanical hard drives are going to be in an anti-vibration mount in my new Lian Li case, and I'm going to be lining the case with sound damping foam anyway.

The GentleTyphoons are great. I've used plenty of fans for heatsinks and they've been the best as for cooling ability/noise. The 1850rpms are quieter than most 1600rpm case fans.

I'll check 'em out.

 

[night_2004]

Ended up putting in some of the case fans that I had from my old build, even though there are some great recommendations on this thread for fans I already have these and there was no harm in my trying them. I think I got better than I would have hoped for with these fans.

Great recommendations for fans, I'm keeping them in mind for if/when one of my case fans or CPU fan dies on me. But for now, case closed!

Thank you for all the help.