Air Flow Sensor

Hi guys

I have been searching everywhere for a air flow sensor where I can measure the volume (i.e. l/s) of air going though a pipe. The only ones that I have found is for liquid.

http://www.ebay.co.uk/itm/New-1-30L-min-1-2MPa-1-2-Flowmeter-Control-Water-Flow-Sensor-for-Arduino-FOK-/172133818859?hash=item2813f9a1eb:g:~c8AAOSwP~tW5s3C

I have also thought of using the following sensor:

https://moderndevice.com/product/wind-sensor/

Knowing the diameter of the pipe and the speed that which the air is travelling at, I should be able to calculate the volume.

Does any know of actual air flow sensor out there, that I can tinker with?

a single pitot tube possible? differential pressure sensors along til pipe?

A lot on automotive fuel injection systems use mass air flow sensors. Could probably get them pretty cheap at an auto wrecker.

There are a number of ways of measuring the airflow (hot wire anemometer is one, another involves ionizing the air at a point and seeing where the ions hit the wall of the tube (I think it was Doric that made one like that). This was from a project I worked on trying to measure airflow 40 years ago (eeeeek - was it really that far back? ). Anyway, one of the big issues to deal with is the boundary conditions - the airflow at the wall of the tube is 0 and then full speed near the center. Between those two points, it does strange things that you need to be aware of when you are trying to calculate the airflow/velocity.