Air Flow Measurement

I think you can use ut flux gauge for the measuring. high temperature or ordinary temperature? info@ndt.cn

Im not sure how big your pipe is but i would run down to the local autozone and get a gm mass airflow sensor, course you would have to figure out how to measure the output of the sensor but that should not be to hard to do

Google "anemometer". You will get lots of hits. or try http://www.pcwi.com.au/

Depending on the amount of money and precision you want. Most are relatively cheap.

Most can test air flow and at least basic Temperature. But you can get some that will also test humidity, wet and dry bulb temperature, Altitude, Air pressure. etc

I assume you want to know the CFM the forced draft fan is producing. A quick, easy and reasonably accurate way (inexpensive also) to measure, is by traversing the duct using a pitot tube and manometer to measure the velocity and static pressures. To improve the accuracy, you need to measure the air temperature to correct for air density. These numbers then can be used along with the area of the duct to arrive at the CFM. Go to a fan or blower manufacturer's web site (Bailey Fan or New York Blower) for engineering info and equations and formulas to convert your information.

The standard way to do this is with a pitot tube connected to a manometer. Do a traverse across the duct and measure the differential pressure by measuring the differential level at the manometer given the density of the manometer fluid. Use the formula "differential pressure=0.5 x density x (velocity^2)" to find the velocity at each point on the traverse. What will become evident is that the velocity away from the walls of the duct is more-or-less uniform. Take a view on the velocity profile across the duct in formulating the average velocity in the duct, and multiply by the duct area to produce the volumetric flowrate. Voila!

There are many ways of measuring the airflow, selecting the best one is the awkward part.

You need to take into account accuracy you require, temperature it has to operate over, both the air flow and the ambient temperature. Speed of response, calibration stability over time, remote or local sensing, any maintenance or service problems, what power sources are available, are there any safety aspects...

So many variables... and all you've said is you need to measure airflow!

The 'best way' to measure what you want will need to have all these questions answered to be able to arrive at a suitable solution.

John.

Air conditioning equipment suppliers (Shop not manufacturer) will sell you a device which is specifically designed for your task.

They are not terribly expensive and may be available from equipment hire places for one off applications or you could ask for a Demonstration at your workplace....

Check Dwyer & Bacharach for meters to measure draft pressure & flow.