Mechanical Analysis of the Critical Conditions for Trapping and Detachment of Microscale Air Bubbles on the Pure Water Freezing Front

Abstract

Icing is a widespread phase change phenomenon with implications for daily life and industrial production. Air bubbles form on the freezing front of pure water with dissolved air during the icing, which may affect the physical properties of ice. Controlling the behavior of air bubbles will be one method to change the physical properties of ice. To analyze the critical conditions for trapping and detachment of microscale air bubbles on a pure water freezing front, a mathematical model describing the forces on air bubble is developed on the basis of the principle of force equilibrium. Results show that the average accuracy of the present model in predicting the average air bubble detachment radius is about 62%, which is 30% higher than the model with the best prediction accuracy in the literature. Buoyant, temperature gradients, and hydrodynamic forces push air bubbles to detach from the freezing fronts, while adhesion force and gravity impede their detachment. Temperature gradient and adhesion forces are the main factors affecting the detachment of air bubbles from freezing fronts. The temperature gradient has the greatest effect on the air bubble detachment radius, while the tilt angle and liquid density have a lesser effect. When the temperature gradient is increased from 1000 to 10 000 K/m, the air bubble detachment radius decreases by 37.78%. Studying the forces acting on the air bubbles on the pure water freezing front is an important reference for the production of special ice bodies, phase change cold storage, and de-icing technology.