Numerical Simulation of Single Argon Bubble Rising in Molten Metal Under a Laminar Flow

The fundamental aspects of rising argon bubbles in molten metal for a laminar flow were investigated by numerical simulations. The Volume-of-Fluid (VOF) model was used to track the interface between argon and liquid metal. The process of a bubble rising in the molten metal includes two steps, one is the bubble rising inside the liquid, and the other one is the bubble rising across the liquid surface. The bubbling dynamics inside the liquid phase was studied in terms of the bubble's trajectory, shape and terminal velocity over a wide range of bubble diameters. It shows that approximate to 3-10 mm bubbles rise in a spiral way with strong instabilities by changing their instantaneous shapes, while approximate to 10-20 mm bubbles rise rectilinearly and their shapes are kept almost steady. All these bubbles' terminal velocities are around 0.3 ms(-1), which are in accordance with literature data. For a bubble with a specific size, small metal droplets can be formed due to the bubble bursting on the free surface. In a situation when the top surface of the bubble is ruptured, the remains of the bubble will collapse and jet droplets can be formed. Simulations of jet droplets were qualitatively analyzed. It shows that when the surface tension is 1.4 Nm(-1), the critical bubble size is 9.3 mm. Also, the ejection is found to increase with an increased surface tension value, unless a critical bubble size is reached.