Being that type of guy, I had to measure the airflow through the inline duct fan intended for the soon-to-arrive laser cutter:
The fan is on the inlet side:
The outlet side consists of flow straightening blades around the backside of the motor mount:
The duct ports on each end are (nominal) 6 inch, with the larger central body about 7 inch ID around the blank-faced 5 inch OD motor mount.
I measured the air speed (in m/s) at the rim of the outlet port and at the center, with the rim speed about twice the center speed. The anemometer is an inch in diameter, so I assumed the annular flow was about 1.5 inch thick.
Subtracting the dead zone in the middle from the total area of the fan body gives the area of the annulus carrying most of the moving air:
|Dia inch||Area in^2||Area ft^2|
Remember, the central dead zone isn’t quite dead: it has an air speed maybe half of the annulus.
More spreadsheet action finds the flow for each of the fan speed settings:
|Speed||Outer m/s||Outer ft/m||Uniform CFM||Annulus CFM||Inner ft/min||Inner CFM||Total CFM||Rated|
The Uniform CFM column assumes a uniform air flow through the whole pipe, which is obviously incorrect. The Total CFM equal to the sum of the Annulus and the Inner zone, which comes out pretty close to the Rated values in the last column, taken from a comment by the seller.
Hard to believe I did the figuring before finding the “right” answers.
This is, admittedly, in free air without ducts or elbows, so the results will be lower when everything gets hooked up.