Study on Two-Phase Flow Instability in Helical Tube under Rolling Condition

Spiral-tube steam generator has the advantages of compact structure and strong heat exchange capacity, and it becomes increasingly prevalent in reactor design. However, its flow and heat transfer characteristics are different from those of straight-tube heat exchanges under marine conditions. Particularly, the instability of two-phase flow under rolling condition remains inadequately explored. In this study, the experimental study on the two-phase flow instability of a single helical tube is carried out under static and rolling conditions, and the process of its transition from single-phase flow to density wave pulsation and then to pressure drop pulsation under different heating power levels is studied. Under the static condition, when the heating power is low, the fluctuation range of each parameter of single-phase flow in the helical tube is within 1%. When the heating power reaches 11 kW, the density wave pulsation with a period of 4.4s is generated, and when the heating power reaches 13 kW, the pressure drop pulsation with a period of about 34.3s is generated. Under the rolling condition, the rolling motion and pulsation have a significant compound effect, and the fluctuation period and amplitude have changed. By studying and processing the experimental data, the characteristics of the period and frequency of the two-phase flow instability in the helical tube are obtained, and the mechanism that causes the difference between the two-phase flow instability in the helical tube and the straight tube flow channel is revealed, as well as the influence mechanism of the rolling condition on the two-phase flow instability.