Is there a direct relation between fan speed and CFM?

[mb]

I guess the title says it all... I have a 92mm Vantec Tornado fan on my CPU, and I was just curious to know how much air it is pushing when it is only spinning at 2500 RPMs, which is the slowest and obviously quietest it can go with my fan controller.

 

[furballi]

More rpm, more air flow up to the point of cavitation. There will be a point where additional rpm will no longer result in more CFM (cavitation).

 

[PurdueRy]

Originally posted by: furballi
More rpm, more air flow up to the point of cavitation. There will be a point where additional rpm will no longer result in more CFM (cavitation).

He's looking for the relationship, not the obvious.

As in, is the relationship linear, quadratic...and so on.

 

[corkyg]

Unless you assume a constant size and blade design/angle, there is no true relationship. A big fan turning slowly can move more air than a small fan turning quickly. There are also differences that can be based on blade design. Fan speed can also relate to noise even on a single given fan.

 

[PurdueRy]

The answer to your question is that it is a linear relationship. So half the fan speed gets you half the CFM.

More information can be found at this site:

http://www.nmbtech.com/html/fans/engineering/engineering_101.html

 

[PurdueRy]

Originally posted by: corkyg
Unless you assume a constant size and blade design/angle, there is no true relationship. A big fan turning slowly can move more air than a small fan turning quickly. There are also differences that can be based on blade design. Fan speed can also relate to noise even on a single given fan.

He assumed the same fan.

 

[mb]

Thanks, PurdueRy. That link has a lot of stuff I don't understand but the graphs pretty much sum it up nicely.

You are also correct that I assumed the same fan (ie everything constant except for the change in fan speed and its effect on airflow).

 

[PurdueRy]

Originally posted by: supafly
Thanks, PurdueRy. That link has a lot of stuff I don't understand but the graphs pretty much sum it up nicely.

You are also correct that I assumed the same fan (ie everything constant except for the change in fan speed and its effect on airflow).

Yup the equations you are looking for are about 3/4 the way down