CFM Calculation for a Fan?

First you need a copy of the fan cuve, which should give CFM or L/s against a total resistance and at an RPM.

If you have the fan and not the curve document measure the inlet if it is a centrifugal or the diameter if it is an axial (propeller) then contact a fan manufacturer and ask for a performance curve for a fan of their manufacture with similar dimensions.

If you don't have a fan at all, you need to establish the duty you require and then contach the friendly sales dept of the friendly fan manufacturer to make a corresponding selection for you in CFM.

Good luck

Fan dia is = 1100 mm

fan rpm is = 1460

Fan degree 10

cfm = ?

The nearest I have to look at is a 1000mm fan 12deg pitch at 1400 RPM gives 24,800 CFM in free air. It will draw 13 amps @ 220VAC it will deliver 5300 CFM @ 1.5"wg Hope this can help

Phil

Phil thank u

please write general formula of this I donot know how to you calculate I am waiting your reply

best regards

Abdul

Abdul.

The figures I gave are NOT from a basic calculation but interpolated from a suppliers catalogue (soler & palau) hope this helps you.

Phil

gives 24,800 CFM in free air. It will draw 13 amps @ 220VAC it will deliver 5300 CFM @ 1.5"wg

I hope you mean 13 amps for 5300 cfm and not 24,800....gotta be a typo.

Most forward curve fans are not made for free air duty, they require some static on one

side at least ( especially with direct drive motors )

Hopefully our guest lets the professionals select his fan for the application he has or he can just do some studying on fan laws.... a complete science in itself.

Phil gave your reply. I recall having 2 pages of formulas on fans only. Presently am in a tour and next week paste all what I have .

A formula I find useful for estimating purposes:

bhp = (cfm*fan pressure)/(6356 * efficiency)

bhp = brake horsepower, fan pressure in inches H2O, efficiency in percent

If efficiency is not known (usually), 62.8% is the rule of thumb and the equation reduces to:

bhp = cfm * fan pressure/4000

fan pressure is total pressure across the fan.

When you say you want to "calculate the CFM" of a fan, are you talking theoretical, actual, load, no load etc. For real-world applications, there are many variables that must be considered - The static pressure being exerted on both sides of the fan can play a big role in altering the CFM.

For real time CFM measurements, one would typically perform a pitot tube traverse with a manometer (or hot wire anemometer) and refer to the appropriate conversion tables to determine volumetric air flow, or utilize a velometer, or a balometer (do a search for alnor instruments) to obtain volumetric air flow data directly.

CFM depends on blade/fin design and other factors. Fan manufacturer will have info. Any generalized calculation is just, general.

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