Bubble formation and dynamics in a quiescent high‐density liquid

Abstract

Gas bubble formation from a submerged orifice under constant‐flow conditions in a quiescent high‐density liquid metal, lead–bismuth eutectic (LBE), at high Reynolds numbers was investigated numerically. The numerical simulation was carried out using a coupled level‐set and volume‐of‐fluid method governed by axisymmetric Navier–Stokes equations. The ratio of liquid density to gas density for the system of interest was about 15,261. The bubble formation regimes varied from quasi‐static to inertia‐dominated and the different bubbling regimes such as period‐1 and period‐2 with pairing and coalescence were described. The volume of the detached bubble was evaluated for various Weber numbers, We, at a given Bond number, Bo, with Reynolds number . It was found that at high values of the Weber number, the computed detached bubble volumes approached a 3/5 power law. The different bubbling regimes were identified quantitatively from the time evolution of the growing bubble volume at the orifice. It was shown that the growing volume of two consecutive bubbles in the period‐2 bubbling regime was not the same whereas it was the same for the period‐1 bubbling regime. The influence of grid resolution on the transition from period‐1 to period‐2 with pairing and coalescence bubbling regimes was investigated. It was observed that the transition is extremely sensitive to the grid size. The transition of period‐1 and period‐2 with pairing and coalescence is shown on a Weber–Bond numbers map. The critical value of Weber number signalling the transition from period‐1 to period‐2 with pairing and coalescence decreases with Bond number as , which is shown to be consistent with the scaling arguments. Furthermore, comparisons of the dynamics of bubble formation and bubble coalescence in LBE and water systems are discussed. It was found that in a high Reynolds number bubble formation regime, a difference exists in the transition from period‐1 to period‐2 with pairing and coalescence between the bubbles formed in water and the bubbles formed in LBE. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3996–4012, 2015