Abstract: VOF (Volume of Fluid) model is employed to study the behavior of single bubble at nozzle of vertical flat pipe. The process of bubble expansion and detachment is simulated, and the influences of immersion mode, nozzle diameter, gas velocity, liquid density, and surface tension on bubble expansion detachment time and detachment diameter are comparatively analyzed. Results demonstrate that the bubble expansion and detachment time shortens with the increase of gas velocity at the nozzle, and then tends to be gentle gradually under three different nozzle immersion modes. In the bottom-immersion and top-immersion mode, the bubble expansion detachment time and detachment diameter both increase with the growth of surface tension, while decline with the climbing of liquid density. In the side-immersion mode, the bubble expansion detachment time and detachment diameter both increase with the growth of surface tension, whereas the effect of liquid density is subtle. There is a positive correlation between the bubble expansion and detachment time and the bubble detachment diameter. The established mathematical model offers an effective research approach by simulating the formation and motion of bubbles truly.

Key words: gas-liquid two-phase flow, nozzle of vertical flat pipe, VOF, bubble, immersion mode