Liquid flow measurement using phase isolation and an imaging method in horizontal gas–liquid two-phase flow

Abstract

A new imaging method based on phase isolation for the liquid flow measurement of gas–liquid two-phase flow is proposed in this study. A swirler is arranged upstream to isolate two-phase fluids. As the two-phase mixture passes through it, a strong swirl flow is generated. The gas is concentrated into the center of the tube and forms a gas core while the liquid phase is pushed to the tube wall and forms a uniform liquid film, which is where the swirl core-annular flow occurs. After phase isolation, many microbubbles, which are small enough to neglect their body force, appear in the liquid film. These phase-isolation-induced microbubbles are used as tracers to represent the local velocity of the liquid flow. A CCD camera is employed to track the motion of the bubbles at the focal plane and determines the velocity at this position. Then this measured local velocity is converted to the mean velocity of the liquid film by a velocity coefficient based on the similitude principle of the velocity profile. After the flow area of the liquid film is derived from the void fraction measurement by another CCD camera, the flowrate of liquid film is determined. The velocity coefficients which express the relation between local velocity and mean velocity of liquid film are obtained by a calibration experiment. Two conventional industry CCD cameras and corresponding individual LED illuminations constitute the imaging system. The image-processing algorithm was developed using the MATLAB image toolbox. AAir and tap water are used and their superficial velocity are in the range of 3.41 m s−1 ∼ 45.15 m s−1 and 0.022 m s−1 ∼ 0.265 m s−1, respectively. The thickness of liquid film ranges from 72.75 μm to 423.11 μm and the diameter of microbubbles ranges from 11 μm to 35 μm.