Measuring Flow with Annubar

H

Thread Starter

hknclk

Hello,

Should pipeline be full of water for measuring flow with annubar? Actually I'm thinking that there is no need for being full of water in the pipeline because annubar gets pressure values from different annulars after then average value of those pressures have been taking into account.

If one of four annulars cant send any value to transmitter so it will be zero and it wont be taken into average account.

Do I think wrong about that issue?

Thanks for reply from now
 
it will be a meaningless measurement, so you might as well remove it or disconnect the transmitter.

your options are best covered with the supplier, and design engineer, and the process designer, if they have not already been fired for incompetence.
 
W
If the pipe is not full, you will not get an accurate flow reading. Your differential pressure readings may be accurate, at the pitot tubes that are submerged, but the flow reading will be wrong. You can't change that.

Walt

Walt Boyes, Life Fellow, ISA; Fellow InstMC
Chartered Measurement and Control Technologist
Spitzer and Boyes LLC

**Spitzer and Boyes LLC publishes the Industrial Automation and Process Control INSIDER (www.iainsider.com)**
 
To get a flow reading that is meaningful, the pipe needs to be full of liquid.

The requirement for a full pipe for flow measurement is assumed, so sometimes a statement to that effect is omitted from flow element or flow meter spec or data sheets.

The original Dietrich Standard spec sheet stated that its Annubar flow element did not meet stated accuracy specs for two phase flows (liquid and gas or liquid and air):

3.2 Functional limitations
For the Annubar to produce accurate, repeatable flow measurement, the following must be considered
<snip>

3. the Annubar will not accurately measure two-phase flow

A scan of the original spec sheet is here:
http://legacy.library.ucsf.edu/documentStore/a/y/q/ayq47e00/Sayq47e00.pdf
(take out any spaces the forum inserts into the URL)

Air and liquid or gas and liquid is two phase flow.
 
W
What is not being explained is that the annubar is a velocity type flow meter, e.g. the meter essentially measures velocity, and then the velocity is then multiplied by the known pipe ID to get volumetric flow (F = Velocity x Area). So even if you have gotten a differential pressure representative of the flowing velocity of the material in the pipe (and that may be questionable as the annubar's averaging annulus and probably the down stream static pressure port may not be liquid full to give you a good differential pressure reading), you would still not know the area of the flowing material (e.g. it is no longer the Pipe ID because the pipe is not full), so you could not get an accurate volumetric flow measurement.

William (Bill) L. Mostia, Jr. PE
ISA Fellow, SIS-TECH Fellow,
FS Eng. (TUV Rheinland)
SIS-TECH Solutions, LP

Any information is provided on Caveat Emptor basis.
 
Top