Parameter Measurement and Flow Pattern Study on Gas-Liquid Two-Phase Flow in Vertical Helically Coiled Tube

Due to the more complex flow pattern distribution and transition characteristics in the gas-liquid two-phase flow in a helically coiled tube steam generator (HCT-SG) compared to a straight tube, accurately measuring the flow pattern distribution and predicting its transition rules are of great importance for the design and operational safety of HCT-SGs. In the present study, a two-sensor conductivity probe measurement system for measuring two-phase flow parameters in HCTs was developed. By using the conductivity probe, flow parameters of gas-liquid two-phase flow in a vertically HCT with an inner diameter of 8 mm were measured on a water-air two-phase flow experimental system. A high-speed camera was used to record the typical phase distribution characteristics of each flow pattern. The features and transition processes of two-phase flow patterns in the helical tubes were analyzed by combining the two-phase flow parameters obtained from probe with high-speed photographic images. Based on the measurement data from the conductivity probe, the effects of the superficial velocities of the gas and liquid phases on the void fraction, bubble velocity, and bubble length were analyzed, and the correspondence between bubble length, void fraction, high-speed photographic characteristics, electrical signals, and flow patterns was established. It was found that in the range of the present experiment, the flow regimes of gas-liquid two-phase flow in HCT could be divided into four types: plug flow, slug flow, bubble flow, and slug-annular flow. Among them, the two-phase flow parameters distribution range corresponding to the slug-annular flow is the widest, and the range of parameters for this flow pattern is larger than that reported in the literature. © 2024 Science Press. All rights reserved.