Characterising slug flow in a horizontal pipe using bubble image velocimetry

In this paper, we investigate air–water slug flow in a horizontal pipe using bubble image velocimetry (BIV). We show that a good estimate of the ensemble-averaged velocity field can be obtained by tracking the bubbles using a correlation based method, even for highly aerated flows where traditional velocimetry methods such as particle image velocimetry (PIV) are very challenging to implement. The global slug statistics in terms of the translational velocity, slug frequency, and length are compared against measurements from gamma densitometers, showing excellent agreement for a wide range of operating conditions. New insight into the velocity variations of three distinct regions; the slug front, the slug body, and the liquid film, are identified and analysed using BIV. Furthermore, along with the velocity fields, the images were used to obtain an estimate of the bubble density spatial distribution to understand the bubble transport inside the liquid slugs.