Sidebar – Pneumatic Measurements on Fan

I purchased a squirrel-cage blower to use to recirculate air in the cabin, and as a side experiment, I wanted to measure the airflow characteristics of the fan. I tend to geek out on the physics aspects of things, so I set out to measure the zero-flow pressure and the no-back-pressure flow rate, and several intermediate points in-between. In analogy, its like measuring the source characteristics of a power source, where one would measure the open circuit (zero current) voltage, and the no voltage (short circuit) current, and points in between to get the source impedance.

So I rigged up a flow tube with several fixed-sized circular orifices, with dynamic pressure measured on both sides of the orifice to obtain (via the equations for compressible orifice flow) the air flow rate, and then an independent pressure measurement (re: atmosphere) at the fan output.

Measurements indicate (see graph below), that at a fan voltage of 13.5V, the measured airflow vs. back pressure (dots) agrees in shape, and is consistently above the manufacturer’s data (solid curve), which was taken with a fan voltage of 12.0V.

I think if I keep the resistance to flow low enough, this fan will deliver an adequate air flow. Further experiments will include measurement of flow resistance of SCAT and SCEET tubing.

Author: bzvelocity

Building a Velocity XLRG-5

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