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Is there a rule of a thumb equation for the mass flow rate of a stationary axial compressor at sea level, using intake area and RPM? Or do other factors like blade geometry make too much of a difference for such an approximation to be possible?

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  • $\begingroup$ shape of the intake... $\endgroup$
    – Solar Mike
    Sep 15 '19 at 20:50
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In theory, there is. Every fan can be described by characteristic numbers. One is the delivery number $\phi$. It describes the ratio of acutall air flow to theoretical air flow, as given by area and speed and is defined as:

$$ \phi = \frac{4\dot{V}}{u\pi d^2}$$

with $\dot{V}$ as volume flow rate in m³/s, u fan speed at circumference in m/s and d fan diameter in m. Knowing fan geometry and rpm, you can calculate u, knowing density, you arrive at $\dot{V}$ so if you know $\phi$ you could calcualte air-flow fom rpm.

The problem is that you will be ahrd pressed to find delivery numbers for fans (They are usually not given in spec sheets IIRC).

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The design of the compressor makes all the difference. Shape of the blades, number of stages, design of the stators, and the material heat resistance.

Increasing the pressure of the air increases it's temperature so the material properties is a constraint.

There is a compromise between compressors designed for performance, and others designed for reliability. If one goes for maximum mass flow rate, the compressor could stall.

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