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Author Topic: 120mm cpu fan. good idea or bad idea?  (Read 2231 times)

MR.G

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120mm cpu fan. good idea or bad idea?
« Reply #10 on: November 13, 2002, 12:26:00 PM »

a 120mm stacked on a 80mm won't increase your cfm it will however effectively reduce the cfm of both fans.the 120 ducting out the side is a good idea i was thinking of doing that also but decided to splurge on an H2O kit. I was going to use the evercool aluninum fan. about the same cfm as my volcano 9 but much quieter. I also was consider the 2coolpc ducted fan http://www.2coolpc.com/Cooling_Solutions/index.html
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Ni4Ever

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120mm cpu fan. good idea or bad idea?
« Reply #11 on: November 13, 2002, 12:31:00 PM »

You should add a Vantec 80mm Tornado, that thing is crazy! It pumps put 80+CFM at 55ish db's.  
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viridius

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120mm cpu fan. good idea or bad idea?
« Reply #12 on: November 13, 2002, 02:46:00 PM »

Bah.  The Vantecs are just rebranded Sunons and Sunons are poseurs compared to Deltas.  The Delta FFB0812EHE does 80.16 CFM at 52.5 dB.
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"I'm totally going to send ninjas after you." - BalefireX

saint-oni

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120mm cpu fan. good idea or bad idea?
« Reply #13 on: December 03, 2002, 07:03:56 AM »

im using a delta now. it is rediculously loud. if i wanted to use a sunon or a delta, id just stick an airplane turbine in my computer, it would probably be quieter.
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Mick

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120mm cpu fan. good idea or bad idea?
« Reply #14 on: December 03, 2002, 07:15:01 AM »

I read somewhere that fans on adapters don't move as much CFM without the adapter. I don't know by how much it would weaken the air flow but if I remember it was saying something like Computer fans are somewhat poor with static pressure (someone correct me if needed). That means that since the adapter compresses the air (Big opening to small opening) the fan has to work harder to acheive the necessary air pressure. I think it said that Computer fans are designed to move their fins fast (RPM's) but with lower torque or something similar. They gave a dremel as an example: It rotates fast but with little torque.  

I don't know, someone know anything more about this>? I think it was in a forum post here somewhere.
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slayer5002

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120mm cpu fan. good idea or bad idea?
« Reply #15 on: December 03, 2002, 12:17:32 PM »

I had a 80mm fan kinda sitting above my processor, I used duct tape and cardboard to make a duct that would blow cool air directly into the processor fan, which then went straight out through my back fan.  My cpu temp went down significantly.
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strongShock

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120mm cpu fan. good idea or bad idea?
« Reply #16 on: December 03, 2002, 02:25:47 PM »

what mick said is right, except there are ways to qualitatively estimate pressure build up. the flow area of the 120mm fan is:

A1 = pi*(60^2 - Ri^2), where Ri is the radius of the inner hub.

ideally that flow area should be less than or equal to the flow area of the 80mm heatsink (no stacked fans):

A2 = pi*40^2 = 5026.5 mm^2 >= A1

the result is:

Ri <= 45mm

this means if a 120mm fan has a hub no larger than 90mm in diameter & some distance is provided between the 120mm fan & the heatsink, zero convergence will occur, the pressure build up is zero, & the air velocity will equal the normal exit velocity of the 120mm fan (theoretically). as the hub (flow exit) gets smaller, more convergence occurs, more pressure is built up, & the flow speeds up.

there will always be some pressure build up from the fins of the heatsink, but remember that a little pressure is good. converging the flow builds up pressure, which speeds the air up & gives far better cooling (via turbulence & a reduction in air heating time). you don't want to "pinch the flow" exit too much, because it is possible to reduce cooling power by creating too much back pressure. there is a "sweet spot"; an exit area that maximizes cooling. to find the ideal area requires experimentation.

OK, i'll shut up now. :roll:
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DSLaBuda

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120mm cpu fan. good idea or bad idea?
« Reply #17 on: December 03, 2002, 06:32:30 PM »

um.... wow, makes suggesting the 152cfm 120mm fan here http://www.kdcomputers.com/eui/prime/profile/479/24/component.htm seem a little stupid without calculating the effects....

guess i shouldn't suggest it without a littel forethought ;)
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strongShock

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120mm cpu fan. good idea or bad idea?
« Reply #18 on: December 03, 2002, 09:32:58 PM »

not stupid at all, as long as you have some experience with a mod, calculations aren't needed. ie: common sense can be more valuable for estimating things than doing extensive calculations. one could go for days on pages with theoretical calcs, while coming up with the same practical solution as someone who just used their intuition & experience. (jeez, my profs would kill me if they saw that, "intuition". i wouldn't write it if i didn't think it's true. for most PC mods, intuition can go a long way before needing mathematical verification).

mathematician: "my 30 pages of theoretical physics show X% inefficiency when using that big fan in that hole... so i'll use the slower fan because it will work better"

PC modder: "with all the air that fan pushes, i doubt it'll run smoothly in such a small hole. i'm using the slower fan cause i think it'll work better."

see, different thinking but the same solution. the only difference is for intellectuals, "thinking & knowing".
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daymar

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120mm cpu fan. good idea or bad idea?
« Reply #19 on: December 03, 2002, 11:33:36 PM »

Well.. I was thinking of something similar but couldn't decide if putting a 120mm fan directly over my hsf would be such a good idea.  But my reasoning was a tad bit more simplex than yours..  Big fan pushes too much air for little fan to keep up with == bad air flow..

I've seen seen propellars/blades slow down when they don't have enough air to pull, so I figured too much air would also be a bad thing.. which goes along with all your compression and pressure mumbo-jumbo.  :)
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