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Are there point in cfm that more air flow don't matter?

post #1 of 14
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I am curious about somethings.
I notice running Heatsink with high cfm fans lower the temperature, but at some point there has to be a break even point where more air flow won't matter anymore.
And at some point will friction come into play with air flow?
I think everybody who got silverstone 110cfm fan upgrade on their heatsink had about 2c to 4c decrease in their temperature than the stock heatsink fan.
But what if you go more? Like delta fans?
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post #2 of 14
deltas will still give lower temps...but there is a point where more airflow isn't gonna help...the copper can only move so much heat.
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post #3 of 14
Good question!

The "Law of Diminishing Returns" applies to any action/reaction. I tried to find this answer myself (I'm somewhat obsessive/compulsive) to no avail.

There must be an equation of variables out there that expresses this in a way that is useful to us. Does anyone have a clue? ...

'cause I sure as heck don't.
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post #4 of 14
It would make no difference at ~10000 CFM i'd guess

not really, but it would be pretty ridiculously high none the less. It wouldn't be friction that tips the scales, but the fact that the CFM-T relationship is probably some form of inverse exponential (a/x^b)
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post #5 of 14
Quote:
Originally Posted by rabidgnome229
It would make no difference at ~10000 CFM i'd guess

not really, but it would be pretty ridiculously high none the less. It wouldn't be friction that tips the scales, but the fact that the CFM-T relationship is probably some form of inverse exponential (a/x^b)
or the fact that you can only cool what the copper brings out of the core..

so just figure out the heat transfer rate for copper, and that's how you'd figure out your little equation. You can only cool to ambient temps with a fan...
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post #6 of 14
Quote:
Originally Posted by Sideburns
or the fact that you can only cool what the copper brings out of the core..

so just figure out the heat transfer rate for copper, and that's how you'd figure out your little equation. You can only cool to ambient temps with a fan...
the thermal conductivity of copper is so much higher than that of air that I would guess that the copper could never be the limiting agent in practical terms.
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post #7 of 14
@sideburns

I dont know if it would even be that simple. If all transfer rates where the same between copper heatsinks then we could just buy the cheap one.

pink
post #8 of 14
Better designed heatsinks work better because they weed out inefficiencies. If you are taking cooling to the extreme at which more CFM yeilds no more performance, the inefficiencies would probably be negligible, allowing us to simplify the problem by ignoring them
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post #9 of 14
There's a point where the benefits start to decrease exponentally as the noise starts to increase exponentally. I think that's called DELTA
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post #10 of 14
Thread Starter 
Some sites had tests where they put fan on and start increasing fan speed, which also raise cfm.
I found this while I try to find more information about Tower 112 that I think I'm gonna get.
They did tests where they use 1x92mm fan, 2x92mm fan, 1x120mm fan with duct, 2x120mm fan with duct on tower 112.
These where the datas.

Quote:
Tested on- P4 3.6Ghz 1.65v 140w
Heatsink- Tower112
Ambi temp-22c

rpm---1x92mm(idle/load)--2x92mm(idle/load)
1500------40/60-------------34/51
3000------33/45-------------30/40
4500------32/41-------------30/37
6000------32/40-------------29/36

rpm---1x120mm(idle/load)--2x120mm(idle/load)
1300------37/57-------------32/47
2600------32/43-------------29/36
4000------31/40-------------29/33
I see, the amount of decreasing temp on every raise of rmp lowers as it get closer to ambi temp. Kind of obvious but its cool.
This might help other tower 112 users.
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