Analysis of critical conditions for air bubble detachment from freezing fronts under different gravitational environments

Extraterrestrial water resources like water ice are essential for space activities. Exploration of ice formation processes in different gravitational environments will contribute to developing and utilizing these water ice resources. The formation of air bubbles on freezing fronts during icing is a common phenomenon, and their behavior of detachment or trapping directly affects ice properties. Mathematical modeling of the forces acting on air bubbles on freezing fronts is developed to investigate air bubbles' detachment and trapping conditions under different gravitational accelerations. The main forces affecting the state of bubbles are the lift force composed of buoyant, Marangoni, and thermomolecular forces, and the drag force composed of adhesion force and gravity. The equilibrium of the lift force and drag force is the critical mechanical condition for air bubble detachment and trapping, and the bubble radius at this time is defined as the critical detachment radius. The experimentally validated mathematical model predicts the air bubble detachment radius with an accuracy of > 65%, which is higher than the 30% of the existing model. The analysis reveals that among the forces affecting the bubble state, the Marangoni and adhesion forces are the dominant factors. The tilt angle of the freezing front, temperature gradient, and liquid density affect the bubble detachment radius, with the temperature gradient having the greatest effect. The study of the critical conditions for air bubble detachment and trapping under different gravitational environments can provide references for engineering applications such as space activities, metal casting, anti-icing, and deicing, as well as enrich the liquid-solid phase change mechanism.