Experimental study of interfacial characteristics of vertical upward annular two-phase flow in 25.4 mm ID round pipe

Understanding the interfacial structure and dynamics of annular flows is essential for the accurate modeling and safe operation of industrial systems involving two-phase flow. This study utilizes the droplet-capable conductivity probe (DCCP-2), a three-sensor instrument designed to overcome the limitations of conventional conductivity probes by enabling the simultaneous detection of dispersed liquid (droplets), continuous liquid (ligaments), dispersed gas (bubbles), and continuous gas core in annular and related flows. The DCCP-2 utilizes a specific signal processing approach to distinguish between these flow structures, providing high-resolution local measurements of volume fraction, interfacial area concentration, velocity, and chord length. Experimental results from 5 distinct annular flow conditions in a vertical air–water loop were obtained. The results reveal clear differences in the interfacial characteristics of the flow fields in annular, wispy-annular, and rolling annular flow. The local measurements agree well with the drift flux model. These findings demonstrate the capability of the DCCP-2 to resolve complex interfacial dynamics in high void fraction flows, supporting the development of improved constitutive correlations and experimental data needed to support computational models for multiphase heat and mass transfer systems.