Bigger Blades or More Blades = Greater CFM?

[VashTheStampede]

I'm sitting here looking at my spare 120mm fan and wondering can make it better, put out more CFM. Would bigger fan blades or more fan blades produce more CFM than stock?

A few ideas on more blades, more smaller blades, of course. Then I thought of what if you had stacked blades turning independently. I wish I knew how to use 3D Studio Max, let alone own a copy, to demonstrate how this would look.

~RT~

[Kingslayer]

There are four things that decide the flow of a fan.

1. Blade number. The more blade surface area, the more air it can push.

2. Blade size. Same concept.

3. Blade pitch. You can have the biggest blades in the world, but if they aren't at a decent pitch, it's all a waste.

4. Motor RPM. You can have 1,2, and 3, but if you don't have the motor to drive it, it's all worthless.

But all in all, you need all four at the highend for a good fan.

[Thirus44]

go with moe blades

[Mr.Lansing]

I would say that big blades will be beta than smaller blades but more blades
cause the bigger the fan is the more the CMF's will be

[RedDeathDrinker]

You want more airflow? Take a look at the article on the front page on centrifugal blowers..........

[docJ]

If you use larger blades or more pitch to increase the CFM of
the fan, you will increase the load on the motor. This may cause
it to slow down and not increase the CFM anyway. If it does not
slow down the motor, the increased load may shorten the life
of the fan motor by causing it to overheat. The motors on most
fans a designed to run at a specific rpm range and load, when
you go outside these limits bad things happen. Most of the time
it is smoke.

[The Overclocker]

Originally posted by RedneckTech
I'm sitting here looking at my spare 120mm fan and wondering can make it better, put out more CFM. Would bigger fan blades or more fan blades produce more CFM than stock?

A few ideas on more blades, more smaller blades, of course. Then I thought of what if you had stacked blades turning independently. I wish I knew how to use 3D Studio Max, let alone own a copy, to demonstrate how this would look.

~RT~
bigger and long fan blades work better, that is why 60mm fans are worse the 120mm fans and generally 25mm high fans are worse the 35mm high fansbecaus ethe fan blades are wide so when the air comes off them it goes in a straighter line

[VashTheStampede]

Would putting just a faster motor in it produce more CFM? Mwuaha fear my 5000 RPM 120mm fan.

~RT~

[cjtune]

Originally posted by docJ
If you use larger blades or more pitch to increase the CFM of
the fan, you will increase the load on the motor. This may cause
it to slow down and not increase the CFM anyway. If it does not
slow down the motor, the increased load may shorten the life
of the fan motor by causing it to overheat. The motors on most
fans a designed to run at a specific rpm range and load, when
you go outside these limits bad things happen. Most of the time
it is smoke.

High-rpm small (60mm) fans, if you've noticed, takes in as much more power as 80mm fans simply because it is more inefficient at that size (more effort due to pitch and small cross-sectianl area) for the same cfm. The motors and bearings are designed to match the airflow needed (ie. load) so don't worry a 7000rpm will wear out faster than a 4000rpm fan unless there is some additional load (dust on blades, bearing is busted, a lot of impedence from dense heatsink fins or small intake/exhaust,etc.). You can theoretically design a 40mm that supplies as much cfm and/or pressure as 120mm but in the end it'll all come down to efficiency and noise (higher rpm, more blade pitch =noisier) and whether it fits into a small space.