Study on interfacial structures in slug flows using a miniaturized four-sensor conductivity probe

A miniaturized four-sensor conductivity probe is designed to effectively minimize the reported limitations of the previous designs. The new probe is capable of measuring both large and small bubbles. The signal processing scheme is constructed for the probe in such a way that the two-phase parameters of different types of bubbles can be identified and categorized. Image analysis is employed to benchmark the new probe. A good agreement between the experimental data and the theoretical calculation is obtained, which assesses both the measurement principle and the capability of the signal processing scheme. The experimental data are obtained in a 5.08-cm ID vertical co-current air/water loop at two different axial locations of L/D=32 and 64 in slug flow conditions. The local time-averaged two-phase parameters obtained by the probe include the interfacial area concentration, void fraction, interface velocity, chord length, and Sauter mean diameter for various types of bubbles. The measured parameters are categorized in two groups in view of the development of a two-group interfacial transport equation. The development of geometric two-phase flow parameters of each group along the axial direction of the flow duct is well demonstrated.