Experimental investigation of sudden expansion's influence on the hydrodynamic behavior of different sub-regimes of intermittent flow

Sub-regimes of intermittent two-phase flows through a sudden expansion have been investigated experimentally. Two pipes of 30 and 40 mm ID connected by a sudden expansion with aspect ratio σ = 0.562 were used. The study was concerned by Plug, Less Aerated Slug (LAS) and Highly Aerated Slug (HAS) flows. The flow visualization showed that the liquid slugs, for Plug and LAS flows, were broken after crossing the singularity which was not the case for HAS flow. However, in general the sub-regime observed on either side of the expansion was the same. Qualitative and quantitative analysis, by means of flow visualizations and standard deviation of pressure drop signals, showed that the flow presents less fluctuations downstream the singularity. Furthermore, the persistence of slug frequency depends on the nature of the sub-regime.