Bubble growth rate from stainless steel substrate and needle nozzles

Shape Oscillation-Induced Early Detachment of Bubble from a Submerged Microcapillary Nozzle

Bubble growth and detachment are basic phenomena in boiling and water splitting processes and are essential for their heat transfer performance and hydrogen production efficiency. In this study, we investigate the formation and detachment of bubbles from a submerged capillary nozzle. Here, we report a new bubbling regime and term it unstable bubbling, where early and normal bubble detachments coexist. The early detachment leads to the generation of many finer bubbles, ranging from one-fifth to one-half of the volume of the permanently detached bubbles driven by buoyancy. The occurrence conditions for unstable bubbling are identified by developing a regime map. The visualization of bubble-induced liquid flow and energy analysis suggest that the oscillating detached bubble provides excess surface and kinetic energies to the growing bubble, supporting early bubble detachment. Two dimensionless numbers are derived considering the effect of these energies, which can be applied to successfully predict the occurrence of early detachment. The present results not only provide physical insight into bubble interactions but also offer potential techniques for generating fine bubbles.

Modification of the Young-Laplace equation and prediction of bubble interface in the presence of nanoparticles

Bubbles are fundamental to our daily life and have wide applications such as in the chemical and petrochemical industry, pharmaceutical engineering, mineral processing and colloids engineering. This paper reviews the existing theoretical and experimental bubble studies, with a special focus on the dynamics of triple line and the influence of nanoparticles on the bubble growth and departure process. Nanoparticles are found to influence significantly the effective interfacial properties and the dynamics of triple line, whose effects are dependent on the particle morphology and their interaction with the substrate. While the Young-Laplace equation is widely applied to predict the bubble shape, its application is limited under highly non-equilibrium conditions. Using gold nanoparticle as an example, new experimental study is conducted to reveal the particle concentration influence on the behaviour of triple line and bubble dynamics. A new method is developed to predict the bubble shape when the interfacial equilibrium conditions cannot be met, such as during the oscillation period. The method is used to calculate the pressure difference between the gas and liquid phases, which is shown to oscillate across the liquid-gas interface and is responsible for the interface fluctuation. The comparison of the theoretical study with the experimental data shows a very good agreement, which suggests its potential application to predict bubble shape during non-equilibrium conditions.