In this study, a Computational Fluid Dynamics (CFD) simulation has been used to derive the complete understanding of a bubble rising in liquid metals. Till now, bubble stability problems in liquid metal regimes have only been poorly analyzed in the literature. Because of the difficulty of such an experimental validation, no universal correlations have been produced to date. Similarly, bubble shape deformations and terminal velocities in liquid metal are not fully developed topics in fluid dynamics, mostly because of the difficulty of validating such phenomena. The main aim of this study has been to deepen the knowledge on bubble deformation in a liquid metal regime. More specifically, the aim has been to develop new correlations for bubble stability and bubble deformation in liquid metals. An in-house code, PSI-BOIL, has been used for the simulations. A single bubble rising in a quiescent liquid has been simulated for three different sets of materials (Nitrogen+Mercury, Argon+GalnSn, Argon+Steel). The obtained results suggest instability phenomena take place in the bubble dynamics in liquid metals for Eotvos numbers > 1.7. Small bubbles (Eo < 1.7) maintain a stable ellipsoidal shape, while the shape and velocity of larger bubbles (Eo > 1.7) tend to oscillate with at non-straight trajectory. The inviscid approximation works well for bubbles in liquid metals. It has been confirmed that the dynamics and the shape of small bubbles (Eo < 1.7) in liquid metals are only controlled by the Weber number.

Rising bubbles in liquid metals in the presence of magnetic fields is an important phenomenon in many engineering processes. The nonlinear behavior of the terminal rise velocities of the bubbles as a function of increasing field strength has been observed experimentally, but it remains poorly understood. We offer an explanation of the phenomenon through numerical calculations. A single rising bubble in stagnant liquid metal in the presence of an applied horizontal magnetic field is simulated. The observed nonlinear behavior is successfully reproduced; the terminal velocity increases with the increase in the magnetic field strength in the lower magnetic field regions but decreases in higher regions. It is shown that, in the lower region, the increase in the average bubble rise velocity results from the suppression of the fluctuations in the bubble trajectory in the vertical plane perpendicular to the magnetic field, as a consequence of the Lorentz force resulting from the component of induced electric current due to the magnetic field, which (approximately) acts in the opposite direction to that of the flow velocity. For higher magnetic field strengths, the Lorentz force induces a broadened wake in the vertical plane parallel to the applied magnetic field, resulting in a decrease in the rise velocity.

No abstract

No abstract