Numerical Analysis on Gas Pore in Metal Droplet During Gas-Atomization Process

The dynamics of a gas pore within a rotating metal droplet are elucidated through two-dimensional numerical simulations of a liquid-gas two-phase flow model. It was observed that gas pores are ejected earlier for the high rotational speed cases, indicating that the rotational motion of a droplet facilitates the ejection. Detailed investigation of the ejection mechanism reveals that the droplet gradually deforms into an elliptical shape as it spins, and the pores protrude in the direction of its minor axis, eventually leading to ejection. The deformation of pores is found to be caused by the formation of a local low pressure region in the thin liquid film between the pores and the gas phase region outside the droplet. Simulations were also performed by varying the viscous coefficient of the droplet, and it was found that the larger the viscous coefficient, the more suppressed the pore ejection becomes. It was suggested that the suppression of high-speed motion of the liquid phase prevents the formation of localized low-pressure regions, resulting in the suppression of pore ejection. On the other hand, simulations were performed by varying the surface tension coefficient, and the smaller the surface tension coefficient, the longer the time required for pore evacuation. This suggests that the smaller the surface tension coefficient, the longer the time scale of the second-order mode becomes, which is relatively strongly affected by viscosity.