Nuclear Science and Techniques

Abstract: Bubble formation is an integral part of the twophase flow science. Through numerical simulation and experiments using different air flow rates and orifice diameters, the present study aims at investigating the behavior of bubble formation and evolution from vertical wall orifice in quiescent pure water. For the experiments, the images of the bubble formation process under different working conditions were recorded using a high-speed camera and analyzed the entire process. The bubble formation process can be divided into three stages, namely nucleation, stable growth, and necking. According to the obtained results, bubble forms only when the air-phase pressure exceeds the threshold pressure at wall orifice. Due to the influence of the threshold pressure and buoyancy, the bubble volume decreases with an increase in the wall orifice diameter for the same flow rate. Moreover, the volume of fluid method is applied to simulate bubble formation in a three-dimensional model and the ‘‘buffer volume’’ is considered in the simulation model. The simulation results matched well with the experimental data, which proves the existence of threshold pressure and the periodic pressure fluctuation at the wall orifice.

Key words: Bubble formation, Vertical wall orifice, Threshold pressure, Pressure fluctuation