Cooling fan

[old guys rule]

All else being equal would a 7 a 9 or an 11 blade steel fan move the most air?

 

[Canadian1968]

I think a google search on that subject would give you more accurate info. You can probably find wind tunnel or other lab tested results. My bet is more blades , more air.

 

[RJRENTON]

I think a google search on that subject would give you more accurate info. You can probably find wind tunnel or other lab tested results. My bet is more blades , more air.

But, more HP will be required move the air. AND....at what temperature is the air being moved....as hot air requires less HP. AND a larger diameter blade assembly, regardless of the number will move more air at a higher pressure. AND rotating RPM also contributes to both volume and pressure. AND what volume of air is being moved? The DENSITY of the air also must be considered as density effects both volume, in terms of pounds/unit of time and the HP ...... Short answer: it is an easily calculated value but more specifics are needed to provide accuracy and guesses are just that, guesses.....
BOB RENTON

 

[PurpleBeeper]

"all else being equal"....more blades, more air

 

[RJRENTON]

"all else being equal"....more blades, more air

Not necessarily......for your own edification and enlightenment consider the following:
The Affinity Laws for centrifugal fans are used to express the influence on volume capacity, head (pressure) and/or power consumption due to change in wheel speed - revolutions per minute (rpm), and/or

1. geometrically similarity by change in impeller diameter
2. Volume Flow Capacity

The volume flow capacity of a centrifugal fan can be expressed as
q1 / q2 = (n1 / n2)(d1 / d2)3 (1)
where
q = volume flow capacity (m3/s, gpm, cfm, ..)
n = wheel velocity - revolution per minute - (rpm)
d = wheel diameter
Head or Pressure
The head or pressure of a centrifugal fan can be expressed as
dp1 / dp2 = (n1 / n2)2 (d1 / d2)2 (2)
where
dp = head or pressure (m, ft, Pa, psi, ..)
Power
The power consumption of a centrifugal fan can be expressed as
P1 / P2 = (n1 / n2)3 (d1 / d2)5 (3)
where
P = power (W, bhp, ..)
Changing the Wheel Velocity
If the wheel diameter is constant - the affinity laws for change in wheel velocity can be simplified to
Volume Flow Capacity
q1 / q2 = (n1 / n2) (1a)
Head or Pressure
dp1 / dp2 = (n1 / n2)2 (2a)
Power
P1 / P2 = (n1 / n2)3 (3a)
Its easier to calculate than to guess, that way you'll have a better understanding of the results needed and certainly loss costly than "lets try this and see what happens" methodology.
BOB RENTON

 

[PurpleBeeper]

Not necessarily......for your own edification and enlightenment consider the following:
The Affinity Laws for centrifugal fans are used to express the influence on volume capacity, head (pressure) and/or power consumption due to change in wheel speed - revolutions per minute (rpm), and/or

1. geometrically similarity by change in impeller diameter
2. Volume Flow Capacity

The volume flow capacity of a centrifugal fan can be expressed as
q1 / q2 = (n1 / n2)(d1 / d2)3 (1)
where
q = volume flow capacity (m3/s, gpm, cfm, ..)
n = wheel velocity - revolution per minute - (rpm)
d = wheel diameter
Head or Pressure
The head or pressure of a centrifugal fan can be expressed as
dp1 / dp2 = (n1 / n2)2 (d1 / d2)2 (2)
where
dp = head or pressure (m, ft, Pa, psi, ..)
Power
The power consumption of a centrifugal fan can be expressed as
P1 / P2 = (n1 / n2)3 (d1 / d2)5 (3)
where
P = power (W, bhp, ..)
Changing the Wheel Velocity
If the wheel diameter is constant - the affinity laws for change in wheel velocity can be simplified to
Volume Flow Capacity
q1 / q2 = (n1 / n2) (1a)
Head or Pressure
dp1 / dp2 = (n1 / n2)2 (2a)
Power
P1 / P2 = (n1 / n2)3 (3a)
Its easier to calculate than to guess, that way you'll have a better understanding of the results needed and certainly loss costly than "lets try this and see what happens" methodology.
BOB RENTON

Bob, if I'm reading that correctly, it looks like the total fan blade area is more important than the number of blades (makes sense).....but if all things are equal (like blade area, blade angle, etc)....... wouldn't more blades still equal more flow? Or am I missing something?

 

[old guys rule]

I see some racing fans rated at 5 to 6000 RPM but what about he everyday fans. I can't promise that I'll never take it up to a 55 anyway this has been quite a learning experience for me. Really appreciate it guys.

 

[RJRENTON]

Bob, if I'm reading that correctly, it looks like the total fan blade area is more important than the number of blades (makes sense).....but if all things are equal (like blade area, blade angle, etc)....... wouldn't more blades still equal more flow? Or am I missing something?

I think its more a combination of all of the above but influenced by RPM and temperature of the air being moved (density in terms of pounds/hr) and the resistance of flow (static pressure). The pitch angle also influences volume of air at a specific RPM. (IMO...I think the shape of the blade, an air foil, would also influence the volume moved as well). Suggest running a few calcs to prove or disprove the point....
BOB RENTON