Numerical Investigations on Effects of Physical Parameters on Single Bubble Generation from Capillary Needles in Newtonian Liquids

The interphase mass, heat transfer efficiency, and flow resistance are strongly dependent on bubble size in gas-liquid two-phase systems, so it is very important for engineering applications to effectively control bubble size. In this paper, the formation, growth, and detachment of single bubbles in Newtonian liquids based on capillary needles were studied in detail using a volume of fluid method. The authors investigated the effects of gas injection velocity, gravitational level, surface tension coefficient, needle radius, and liquid−phase properties (liquid viscosity and density) on the process of bubble generation, and the effects of the above factors on bubble shape, detachment diameter, and time were analyzed. The results show that an increase in gas injection rate, liquid-phase viscosity, needle radius, and surface tension coefficient can lead to an increase in bubble detachment diameter; however, an increase in liquid-phase density and gravitational level can lead to a decrease in bubble detachment diameter. It is found that the effect of the liquid−phase viscosity on bubble detachment diameter and time is slight, but the effect of gravitational level on detachment diameter and time is significant. Among all the forces, buoyancy, surface tension, and pressure are the most important ones that control the generation of bubbles.