A numerical study on oscillatory characteristics of unstable steam jet in water flow within a vertical pipe

Abstract

In this study, a numerical investigation was conducted to examine the condensation and pressure oscillation characteristics of low mass flux steam jets in water flow within a vertical pipe under different operating conditions. Three bubble states were observed during the injection of subsonic steam in an upward direction into a subcooled water flow: bubble growth, bubble necking, and bubble detachment. Through a synchronously analysis of the bubble morphology and interface pressure, the oscillation mechanism of the unstable steam jet was revealed. The results showed that the pressure oscillation characteristics were consistent with the behavior of the vapor bubble. The frequency of pressure oscillation increased with the increase of steam inlet pressure and water Reynolds number, while decreased with the decrease of subcooled water temperature. The intensity of pressure oscillation exhibited a distinct peak at the position corresponding to the detachment of the primary and secondary bubbles. Moreover, a new predictive correlation for pressure oscillations in flowing water was presented by the frequency of steam injection, the condensation driving potential, the steam mass flux, the Weber number, and the water Reynolds number. The predicted values showed good agreement with the experimental values, with a maximum deviation of 24 %