An improved optical method for spatial phase distribution measurement of slug flow in small channels

Abstract

This work presents an improved optical method which can fully exploit the light intensity distribution information for measuring spatial phase distribution of slug flow in small channels. Two high-speed CMOS array sensors (in horizontal and vertical directions) are used to capture the information of light intensity distributions (including the straight-line and the curved light intensity distributions). A spherical surface geometric model is used to characterize the spatial phase distribution of the gas-liquid two-phase interface of slug flow more accurately. In addition, the measurement correlations between the geometric features of spatial phase distributions and the characteristics of light intensity distributions are analyzed and the measurement model is established. The improved method not only considers the phase distribution characteristics of each independent cross-section, but also extends the correlations and measurement model to the three-dimensional spatial phase distributions through integrating the light intensity distribution information, realizing more accurate profile reconstruction. Experiments are carried out in three small channels with different inner diameters. The reconstructed profiles of spatial phase distributions are in good accordance with the actual images and show more details in the nose and tail parts of the gas slugs, with the maximum average symmetric surface distance of 0.2779 mm. The void fraction is subsequently estimated, with the maximum absolute error of −4.91 % and the maximum root mean squared error of 0.0264. The research results show the effectiveness and enhanced accuracy of the improved method compared with other optical methods, which can provide a useful reference for other related works.