CLOSURE MODEL FOR TWO-PHASE LIQUID-GAS MEASUREMENT UNDER SLUG FLOW CONDITIONS |
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| S. Al-lababidi, M. L. Sanderson |
- Abstract:
- A series of experiments has been undertaken to investigate the behaviour and the performance of a clamp-on transit-time ultrasonic flowmeter in two-phase air/water flow. The results show the performance of the liquid ultrasonic meter to be seriously affected by the presence of free gas in a manner that is dependent on the actual flowrate of the gas and the flow regime. The data presented here covers water/air flow under slug flow regime and an evaluation of transit-time ultrasonic meter and its suitability for two-phase flow measurements. The factors affecting performance are discussed and a closure method using a transit-time ultrasonic flowmeter is introduced.
The closure method for the liquid flowrate employs a mathematical relationship, under slug flow conditions, between the estimated liquid flowrate Q(Estimated); the indicated liquid flowrate Q(Indicated); a velocity profile correction factor, K2(Re); the partial-filled area of the pipe; the cross-sectional area of the pipe and a height correction factor K1(h). This closure method for the gas flowrate uses measurements from the clamp-on transit-time ultrasonic flowmeter, an axial differential pressure transducer and a vertical differential pressure transducer.
The height of the water is obtained by using the vertical pressure transducer and applying the hydrostatic pressure equation. The height of the film reflects at the same time the functional condition of the ultrasonic flowmeter whether it is in a functional state or not. The acceptable height which keeps the clamp-on transit-time ultrasonic flowmeter to continue to function is above 50% of the pipe diameter. An axial differential pressure sensor gives the pressure drop along the slug body. The flowrate of the liquid is constant throughout the tests; the gas flowrate was increased over the range of tests.
Two main correction factors are implemented in the closure model. The Velocity Profile Correction Factor (VPCF), which is a function of Reynolds number K2(Re) for fully developed pipe flow for an assumed Reynolds Number, and the height of the water film correction factor K1(h). The K1(h) correction factor relates the velocity measured along the beam to the mean flow velocity over the entire cross-section of the flowing medium under partially filled pipe conditions.
It is found that the clamp-on transit-time ultrasonic flowmeter can be successfully applied to a horizontal slug flow regime with the application of this closure method to the indicated ultrasonic flowrate Q(Indicated). The average error of the clamp-on ultrasonic flowmeter measurements in two- phase flow were reduced by 50% to 75% and that is dependent on the height of the water, gas flowrate, and the slug flow characteristics. The average error of the estimated flowrate of the ultrasonic flowmeter is ± 3.5% to ± 6.5% relative to the reference turbine flowmeter. Applying a pressure drop closure model at a given liquid flowrate provides an air flowrate measurement with an accuracy of better than ±10%. - Download:
- IMEKO-TC9-2003-063.pdf
- DOI:
- -
- Event details
- IMEKO TC:
- TC9
- Event name:
- FLOMEKO 2003
- Title:
- 11th Conference on Flow Measurement
- Place:
- Groningen, NETHERLANDS
- Time:
- 12 May 2003 - 14 May 2003