- #1

CstmIndctn

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**AirFlow Calculations/ Anemometer anyone??**

Hello all,

I am trying to solve a problem with my anemometer. I am not sure if there is anyone here that has used one but here goes. My purpose is to calculate CFM of a particular AIR INTAKE of my truck. The problems lies in that CFM= Air Velocity Ft/Min X Area ft^2...with Area= PIE * (r^2)...however my intake is 8" diameter at the entrance, then the filter, then a 4" exit...The air supply I am using is (shopvac) 2" diameter hose...what do I use as the area?

I have a chart that says @ 4500 feet per minute on a 4" diameter is 390cfm

2nd question-- What am I doing wrong if I do 3.14 (2^2)= 12.56 Area

CFM= 4500 * 12.56= crazy big number which is not 390cfm =0(