Annubar Discrepancy

They should be different.

I'd guess there's more pressure at the bottom of the stack.

So, probably more flow.

After breakfast, you could look up "laminar flow" for fluid dynamics.*burp*

Most stacks have a smaller inside diameter at the top than at the bottom which will affect the reading of the annubar.

Yes,there should be a difference,influenced by many factors.

Have you considered using a multi-variable transmitter for your process?

It could simplify your measurement and increase accuracy to integrate these measurements into one instrument.

Here is a link to one such instrument:

Good luck.

Confucius say:Man with two watches never know what time it is."

http://www2.emersonprocess.com/en-us/brands/rosemount/pressure/pressure-transmitters/multivariable-transmitters/3051s-multivariable/pages/index.aspx

Eltech,

Can you make a sketch or mechanical diagram for the stack and flow meters? including lengths and diameters

Best regards

JP

No, the readings should not be different, but how big is the discrepancy?

I assume no air is lost between the 2 annubars, or you would have said. In that case the mass flow is the same at both, and since the pressure and temperature won't change significantly over the 20m, the actual volume flows are also equal.

If the pipe area at the 2 annubars is the same, the ΔP should be the same. Is it? If it is, there's a problem with the PLC calc. If not, with the annubar set-up.

If not, the ΔP varies as 1/A², which you can use to compare the ΔP data.

Also you could try putting a known ΔP on each transmitter and check the PLC gives same flow.

The actual pressure at the lower annubar due to the 20m height of air is about 2.4mbar. That causes the ΔP at the lower annubar to be lower by a factor ~ √(1 - 0.0024), a 0.1% change, which is well within the system error.