Read PC Fan Air Movement Amounts

I want to get the amount of air a PC fan can push at certain intervals in a tube- as some can push more air farther while others are are designed for more closer air movements to push air through radiators. Anyways, I am looking for a way to get a physical number for these intervals, and the one way I can think of is to read how fast the air is moving and do some math to convert that to CFM.

I have been trying to look around for some kind of small propeller, because the air movement area is a bit more than 12x12cm in size to match the basic 120mm computer fan. Almost all that I find are sensors to check if there is any air movements, or the bigger air cup anemometer that is too big and would not be easy to motorize the movement of the sensor to those intervals (I do not know what those positions are, but likely anywhere between 0-100 spots in percentage of the way to read of device from forward most position).

you can make your own anemometer. a pin can be the axel and use some hot glue to hold a piece of plastic in place. cut out a round disk from an old credit card, glue on a couple of fins and a magnet make sure is spins easily and put a HALL effect sensor on it. speed of the pulses would represent air speed.

there are lots of water flow sensors that do this so the code is easily available.

google anemometer for ideas.

if you are well experience with electronic circuit design and really good with op-amps, you might be able to make something really nice.

Sorry for the late response, another project swooped in for the week but is now out of the way.

The thing with making my own anemometer, is that I cannot calibrate it properly to count for friction of fan and what not- so whatever I will make, will be off or way off; unless I make my own made up number to represent CFM's