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I am trying to determine the approximate CFM of several axial flow fans being used in agricultural storage in the developing world. The only information the storers have is the power, RPM, and diameter of their fans.

I would like to estimate the CFM at various levels of Static Pressure, and within a range of likely blade pitches.

Is there a way to to do this? I've looked at the fan laws, but it seems like these are meant to calculate changes in variables, not the absolute values of the variables themselves.

Thanks.

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    $\begingroup$ You can't analyze the fan blades at all. You don't know enough about them and the machinery. But you can can establish an upper bound based on current draw, voltage, motor type, and back pressure. That is just an energy balance. The fans probably aren't more than 50% efficient. Belt transmissions maybe 90% efficient. Motor maybe 85% efficient. Found this document Fan Performance Characteristics of Axial Fans $\endgroup$ – Phil Sweet Mar 14 '19 at 21:46
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For a particlar fan blade or impeller type an empirical relationship could be developed. I am not familiar with an empirical correlation of this type for fan or blowers. I have seen empirical correlations for liquid mixing impellers with fitting parameters for specific impeller types to estimate power. To know for a specific geometry fan blade without an empirical correlation I believe you would need a sort of finite element analysis.

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