Experimental study of flow monitoring instruments in air-water, two-phase downflow

The performance of a turbine meter, target flow meter (drag disk), and a gamma densitometer was studied in air-water, two-phase vertical downflow. Air and water were metered into an 0.0889-m-ID (3.5-in) piping system; air flows ranged from 0.007 to 0.3 cu m/sec (16 to 500 scfm) and water flows ranged from 0.0006 to 0.03 cu m/sec (10 to 500 gpm). The effects of flow rate, quality, flow regime, and flow dispersion on the mean and fluctuating components of the instrument signals are also studied. Wire screen flow dispersers located at the inlet to the test section had a significant effect on the readings of the drag disk and gamma densitometer, but had little effect on the turbine. Further, when flow dispersers were used, mass flow rates determined from the three instrument readings and a two-velocity, slip flow model showed good agreement with actual mass flow rate over a three-fold range in quality; mass flows determined with the drag disk and densitometer readings assuming homogeneous flow were nearly as accurate.