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Title: Fluid Composition Analysis By Multiple Gamma-Ray Beam And Modality Measurements
Author: Geir Anton Johansen, Stein-Arild Tjugum
Source: 2007 North Sea Flow Measurement Workshop
Year Published: 2007
Abstract: The feasibility of using multiple gamma-ray beams to identify the type of flow regime has been demonstrated. One gamma-source with principal emission at 60 keV is used because this relatively low energy enables efficient collimation and thereby shaping of the beams, as well as compact detectors. One detector is placed diametrically opposite the source whereas the second and eventually the third are positioned to the sides so that these beams are close to the pipe wall. The principle is then straight forward to compare the measured intensities of these detectors through that identify the instantaneous cross sectional gas-liquid distribution. By counting the intensity short time slots and ( 100 ms), rapid regime variations are revealed. Varying water salinity is another challenge for most multiphase flow meters because it affects volume fraction calculations based on gamma-ray, electrical conductance and other measurements. There have been a few approaches to solve this without relaying on off line calibration. One of these utilizes the difference in the composition of the gamma-ray attenuation coefficient at different energies. The method presented here take advantage of the same effect, but though simultaneous measurements of transmitted and scattered gamma-rays from a 241-Am source. It has been shown that the gas volume fraction then can be determined independent of changes in the water salinity. Once again the challenge is to minimize the effects of changes in the flow regime.

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