Cavity deformation and bubble entrapment during the impact of droplets on a liquid pool

Abstract

The impact of droplets on a liquid pool is ubiquitous in nature and important in many industrial applications. A droplet impacting on a liquid pool can result in the pinch-off of a regular bubble or entrap a large bubble under certain impact conditions. In this study, the cavity deformation and the bubble entrapment during the impact of droplets on a liquid pool are studied by combined experimental measurements and numerical simulations. The time evolution of the free surface profile obtained in the numerical simulation is in good agreement with the experimental results. The cavity created by the droplet impact affects the pinch-off of regular bubbles and the entrapment of large bubbles. The regular bubble pinch-off is the direct consequence of the capillary wave propagating downward along the interface of the cavity and merging at the bottom of the cavity. In contrast, the large bubble entrapment is due to the merging of the liquid crowns at the mouth of the cavity. Gravity and environmental pressure play important roles in cavity deformation and bubble entrapment after droplet impact on liquid pools. The maximum depth of the cavity decreases as the gravitational effect becomes stronger. The phenomenon of regular bubble pinch-off may disappear as the gravity decreases. We find that the regular bubble pinch-off can transform into large bubble entrapment when increasing environmental pressure. The size of the large bubble entrapped decreases with increasing the environmental pressure due to the larger difference in the pressure and the vorticity around the liquid crown at increased environmental pressure. Finally, the regime map of bubble entrapment after the droplet impact is obtained.

Fine Flow Structure at the Miscible Fluids Contact Domain Boundary in the Impact Mode of Free-Falling Drop Coalescence

“…From the first experiments up to the present, most of the attention has been paid to the study of either the geometry of the free surface [3,91] or the motion of the forming ring vortices and vortex systems [1,2,22,23] when studying the flows generated by a drop falling into a liquid. To visualize the flow, the methods of "bright dot" or "backlight" illumination and "black and white flow pattern registration" are mainly employed [86,89].…”

Fabrication and Performance of Bubble‐Containing Multicompartmental Particles: Novel Self‐Orienting Carriers

“…Although particles can be generated in a size-controlled manner by regulating voltage and tip diameter (Figure 2c), the appearance of the bubbles needs to be carefully designed. Rational coordination of droplet impact (controlled by the Weber number, We = 𝜌v 2 D/𝜎, where 𝜌 is the droplet density, v is the impact velocity, D is droplet diameter, 𝜎 is surface tension) [16] and solidification (controlled by crosslinking rate) is the key to this realization; otherwise, there will be bubble-free multicompartmental particles, structurally distorted particles, and diffused particles (Figure 2d). An increase in We number (> 149) means sufficient kinetic energy for particle deformation facilitates the acquisition of ideal particles, but excessive impact (We > 256) leads to structural disturbances.…”