Flow rate vs RPM

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tutrinh

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• Jun 18, 2003

• #1

any relationship between them????
Higher flow rate but lower RPM . I have 2 fan in mind. Which one you think is better

89CFM, 2200RPM very quiet or
90CFM, 3000RPM louder than the above.

 

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sirtoby

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• Jun 18, 2003

• #2

If the difference is only 1 CFM I would definately go for the fan with lower rpm as it's more quiet than the other one..

 

arabarabian

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• Jun 18, 2003

• #3

There is always going to be some relation between CFM and RPM. The chances are the the one that spins slower has a different pitch on the fan blades so therefore making it push more air but requiring more energy.

Thank You,
Daniel

 

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gogetadbl

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• Jun 18, 2003

• #4

More RPM = more energy which could be going to sound, pitch, etc. and not only airflow as the poster above said. Energy is conserved between it all though

 

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Paxmax

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• Jun 18, 2003

• #5

Who knows, one of the fans might be overspecified.

Or, might not be so good for pushing air when it hits a restriction.

 

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Since87

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• Jun 18, 2003

• #6

Paxmax said:

Or, might not be so good for pushing air when it hits a restriction.

Click to expand...

Exactly. The flowrate spec on fans is just one part of the picture. You need to look at the flowrate vs backpressure curve of the fan to know what it can do when faced with backpressure.

 

timmyqwest

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• Jun 18, 2003

• #7

the first one is quiet a bit quiter with the same amount of air movement

 

Caffinehog

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• Jun 18, 2003

• #8

gogetadbl said:

More RPM = more energy which could be going to sound, pitch, etc. and not only airflow as the poster above said. Energy is conserved between it all though

Click to expand...

Well, air resistance varies with the SQUARE of the velocity, so a higer RPM fan with the same CFM will use more energy.

 

oc jason

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• Jun 18, 2003

• #9

ya defintely go for the less rpm for basically the same CFM, i can deal with a low hum sound alot better than a high pitch tornado case

 

OP

T

tutrinh

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• Jun 18, 2003

• Thread Starter
• #10

I just buy a 120mm fan , it is very quiet too me

I bought YS TECH 135CFM, 45db 4100RPM
My Sunon Ultra High Speed 50 CFM, 40db, 3900RPM is way louder than the YSTECH. When I hook them in the case together, all I hear is the Sunon fan spinning. Even though it rate 5db less than the YS, but seriously, it is LOUDER

 

Caffinehog

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• Jun 18, 2003

• #11

More likely it's actually quieter, but it runs at a more annoying, higher frequency.

 

arabarabian

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• Jun 18, 2003

• #12

Sorry let me clarify myself. What I was trying to say is that there are two ways to achieve a given CFM. One you can have the fan spin faster. Or two you can design the blades so that the push more air but require more energy to do so. But the faster the fans are spinning the more noise they generate at a higher pitch. Well I hope that cleared things up.

Thank You,
Daniel

 

anvil82

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• Jun 18, 2003

• #13

tutrinh said:

I just buy a 120mm fan , it is very quiet too me

I bought YS TECH 135CFM, 45db 4100RPM


My Sunon Ultra High Speed 50 CFM, 40db, 3900RPM is way louder than the YSTECH.


When I hook them in the case together, all I hear is the Sunon fan spinning.

Even though it rate 5db less than the YS, but seriously, it is LOUDER

Click to expand...

You just contradicted yourself.

 

OP

T

tutrinh

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• Jun 18, 2003

• Thread Starter
• #14

anvil82 said:

You just contradicted yourself.

Click to expand...

I didn't know until I bought a YS TECH today and test it out. In my mind, I thought it will definitely LOUDER than my Sunon ( since its RPM and db is higher , so it must be louder ), but it is much QUIETER than the Sunon.

 

Lt. Max

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• Jun 18, 2003

• #15

yeah as caffeinehog said, the 120mm is quieter because it has a lot lower pitch than the 80mm fan, the low pitch is like bass you dont really hear it very well but you will hear it more in the next room then the 80mm because lower frequency travels further.. correct me if im wrong

max

 

Toysrme

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Nov 12, 2001

• Jun 18, 2003

• #16

The flow rate - RPM correlation is direct, but about all you can gain is the pitch and blade legnth are more aggressive on the one that spins slower.

I'd get the slower one, less noise.

The faster any blade moves through the air the louder it will be. You go from sucking air in to ripping it in.

Actually that's a bad example, that dosen't happen for a *very* long time, but you get the point heh.