suitable flow measurement techniques for air flow in rectangular ducts.

[arun1990]

Dear all,

I would like to discuss on following points/questions.

1.which flow meter is best to measure air flow in big rectangular ducts of size 12mX9m? and why?

2. I have considered pitot tubes and annubars, but is it possible to use them in rectangular ducts?

3. can standard DP measurement techniques be applied? and if so, what are the possible problems?

4.any other options like anemometers/Electro-magnetic meters or vortex?

thanks a lot all of u in advance..!!

[prajule]

I recommend u to use verabar i.e .velocity averaging flow sensor for below listed advantages

1. Long term accuracy
2. Higher rangeability
3. Non clog design
4. Low permanent pressure loss
5. Minimum straight run requirement
6. Low installation costs
7. Low operating costs


Some problems associated with previous measurement technologies used for duct air flow

1. Airfoil

High permanent pressure loss, difficult to install and maintain, prone to clogging and questionable accuracy due to lack of test data.

2. Thermal Dispersion

Requires testing and calibration at different flow rates, no means of checking calibration and can cause excessive downtime due to particulate build-up and corrosion.

3. Averaging Pitot Array

Difficult to install requiring cutting out duct sections, low differential pressure signal,prone to clogging of sensor ports and no test data to support accuracy and straight run claims.


How it Works

The Verabar senses the natural averaged pressures created by the velocity of the fluid. When the fluid impacts the sensor, it creates a high-pressure zone (greater than the pipe static pressure) in front of the sensor. As the fluid moves past the sensor, it accelerates and a low-pressure zone is created to the sides and rear of the sensor. Alternate vortices are shed as the fluid separates from the sensor and a partial vacuum is formed at the rear of the sensor. Multiple ports are positioned in the high and low-pressure zones and an averaged differential pressure is produced. Verabar’s superior performance is due to its shape, surface condition and low-pressure port location.

* No clogging
* Stable signal
* Low drag and increased structural strength
* Solid one-piece construction

Superior Sensor Design

Developed from aerospace technology, the Verabar averaging pitot low sensor provides unsurpassed accuracy and reliability. With its solid one-piece construction and bullet shape, the Verabar makes flow measurement clog-free and precise. The unique sensor shape reduces drag and low-induced vibration. And the location of the low-pressure ports eliminates the potential for clogging and improves signal stability.

Greater Resistance to Clogging

Clogging can occur in low-pressure ports located in or near the partial vacuum at the rear of the sensor. The Verabar design locates the low-pressure ports on the sides of the sensor, forward of the fluid separation point and turbulent wake area. This virtually eliminates clogging and produces an extremely stable signal.