My Fluid is non-Newtonian, contains about 5% deliberately-entrained air and suspended solids in the form of gel beads and seeds. How can I make my Coriolis mass flowmeter work properly?
--from November 2003 CONTROL
Self-Draining Tube Geometry Recommended
I suspect either one of two failure-mode possibilities: One, the tube won't vibrate due to fluid sloshing that absorbs the tube drive energy, or, it doesn't get a good zero at no flow conditions again due to fluid sloshing. If number one is the failure mode, then a more robust tube-drive technique should resolve your problem.
If the failure mode more closely number two then finding the solution may be a bit trickier. Getting a good zero at no flow due to the sloshing will require some special piping configuration.
I would recommend designs with self-draining tube geometry. There's a chance that your fluid my not allow the bubbles to escape at all if it's really viscous, and sloshing will allow the zero reading to continue to wander. If this is the case, fill the meter with water initially and zero it. Then run your normal process.
Hoag Ostling, Chief Application Engineer
Yokogawa Corp. of America, hoag.Ostling@us.yokogawa.com
Improperly-Sized Coriolis Meter
Most entrained air issues stem from improper Coriolis meter sizing. Coriolis sizing methods use Newtonian viscosity when the non-Newtonian fluid begins to flow. This results in an oversized meter. In some cases, when a meter is applied where the fluid changes from batch to batch, it must drain completely to avoid cross contamination. A straight tube meter may be the only choice in this case.
Tim Patten, Director of Measurement Technology
Air entrainment corrupts the fine-tuning of most Coriolis meters, and they either lose control or shut down completely and can produce large errors. At 5% air you are probably experiencing these effects.
A completely digital Coriolis mass flow transmitter will provide stable control of the flowtubes for amounts of air far in excess of what you are experiencing. These systems contain a patented software-based system providing high-speed re-tuning of the drive for each half cycle of flowtube vibration. There will be no loss of control of the flowtubes, therefore no loss of flow measurement, for even the most chaotic conditions of two-phase flow. Also built in are sophisticated algorithms to deal with the errors introduced by employing Coriolis to two-phase, gas-liquid flows. This should easily solve your problem.
Wade Mattar, Product Manager
Foxboro Company, www.foxboro.com