Numerical Analysis of the Dynamics of Toroidal Bubbles Considering the Heat Transfer of Internal Gas

This paper describes a new numerical method for computing the motion of a toroidal bubble that is formed after a liquid microjet threads the bubble surface. We used the boundary element method combined with the finite volume method to calculate the toroidal bubble dynamics with consideration of the heat transfer inside the bubble. The unstructured triangular grids were used to analyze the internal field. We investigated the bubble collapse near a plane rigid wall. The results show that the initial bubble radius affects the motion of the toroidal bubble, the temperature fields inside the bubble and the pressure fields outside the bubble. When the initial radius is small, the internal thermal boundary layer becomes thick and the bubble collapse is accelerated. This violent collapse induces an extremely high-pressure region near the point of liquid microjet impact. The pressure at a rigid wall, therefore, becomes locally very high when the tiny bubble collapses near the wall.