Bubble Entrapment Phenomena in Liquids
Bahni Ray1,a, Gautam Biswas1,b and Ashutosh Sharma2
1Department of Mechanical Engineering, Indian Institute of Technology Kanpur, Kanpur 208 016, India.
abray@iitk.ac.in
bgtm@iitk.ac.in
1Department of Chemical Engineering, Indian Institute of Technology Kanpur, Kanpur 208 016, India.
ashutos@iitk.ac.in
ABSTRACT
A drop that falls in a deep pool of same liquid can either coalesce with the receiving liquid and form a vortex ring or splash, depending on the impact conditions. When the impact conditions are gradually changed the transition between coalescence and splashing proceeds via a number of intermediate steps. Under certain conditions the impact of a drop on a deep liquid results in the entrainment of a single gas bubble. The bubble is pinched off at the bottom of the crater during the process of crater collapse. This is called regular entrainment. The oscillating bubble emits sound which is the main source of underwater noise of rain. The conditions under which bubble is entrained in this manner can be represented by a region of regular entrainment in the Weber number (We) versus Froude number (Fr) diagram. Bubble entrapment, which results from a competition between concentric capillary pinching of the crater cusp and viscous damping, is captured well by the capillary number (Ca). In this paper the phenomenon of regular bubble entrapment is studied numerically using coupled level-set and volume of fluid (CLSVOF) method. Simulations are found to be comparable with various experimental results. The effects of various fluid parameters are investigated to get a more insight into the phenomenon. Three liquids, pure water, glycerin/water mixtures, and silicon oil have been used to investigate the effect of viscosity and surface tension on regular bubble entrapment.
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