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

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- Thread starter old guys rule
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All else being equal would a 7 a 9 or an 11 blade steel fan move the most air?

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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

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

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

Not necessarily......for your own edification and enlightenment consider the following:

- geometrically similarity by change in
**impeller diameter** **Volume Flow Capacity**

where

q

d = wheel diameter

The head or pressure of a centrifugal fan can be expressed as

where

The power consumption of a centrifugal fan can be expressed as

where

P

If the wheel diameter is constant - the affinity laws for

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

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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?Not necessarily......for your own edification and enlightenment consider the following:

The Affinity Lawsfor centrifugal fans are used to express the influence on volume capacity, head (pressure) and/or power consumption due to change in wheelspeed- revolutions per minute (rpm), and/or

The volume flow capacity of a centrifugal fan can be expressed as

- geometrically similarity by change in
impeller diameterVolume Flow Capacity

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 forchange in wheel velocitycan 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

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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, 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?

BOB RENTON

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