Numerical simulation of bubble rising behavior in a tannin-based foaming precursor resin

A two-dimensional volume of fluid (VOF) model was developed to simulate the deformation of the bubble, the end speed of bubble rise, the distance of bubble rise and the movement trajectory in different initial conditions of tannin-based foaming precursor resin. In this study, bubble rising and coalescence characteristics are connected with parameters of the resin, especially viscosity, surface tension, the initial radius and location of the bubble also matter. The result shows that rising velocity of the bubble decreased as the viscosity increased, and at the same time, the flow rate of the bubble was lower. In addition, with the increase in surface tension, the ability of the bubble to change shape was impeded, whereas when the bubble radius increased, the rising velocity of the bubble was faster. The floating behavior of parallel double bubbles and coaxial double bubbles in resin was simulated. It was found that the distance had important effects on their coalescence behavior. For parallel doubles, the motion process is symmetric, because of their vortices, the bubbles will move away from each other, and their motion properties depend on the relative position of the bubbles which is crucial for the bubble merger. For coaxial double bubbles, the closer the distance between the two bubbles is, the faster the fusion speed will be. When the distance is fixed, the larger the radius is, the shorter the fusion time will be, which proves that there are differences in the growth rate of bubbles during the foaming process.