Determination of Taylor Bubble Properties and Co-Current Upward Slug Flow Characteristics from Experimental Database of Ultrafast X-Ray Tomography

Abstract

Slug flow is characterized by the presence of Taylor bubbles and liquid slugs with small bubbles inside. Investigations about detail properties of Taylor bubbles are necessary to obtain physical mechanisms of slugging phenomena and for the development of new Computational Fluid Dynamics (CFD) models. At the Helmholtz-ZentrumDresden-Rossendorf, experiments on co-current upward air-water flow in 54.8 mm diameter vertical pipe with various gas-liquid superficial velocities were performed. As measurement technique, an ultrafast dual-layers X-ray tomography was developed to fulfil the requirement of an accurate measurement with high spatial and temporal resolutions. The resulted cross sectional image stacks from tomography scanning are reconstructed and segmented to carry out each gas bubble size and parameters. A bubble pair algorithm is implemented to detect the instantaneous movement of each bubble. This method is able to assign the correct paired bubbles from both measurement layers by considering the highest probability of position, volume, and velocity. Therefore, each gas-bubble individual characteristics can be revealed. As the results, Taylor bubble velocities, length, frequencies, and relation between consecutive bubbles are carried out. The three-dimensional movement of the bubbles can be explained through the calculation of axial velocity, horizontal velocity, radial velocity, and movement angle. Relationship between Taylor bubble properties and as well liquid slug to the velocities are also revealed. The reported data are in good agreement with the experimental results in previous works.