Dynamics of two coaxially rising gas bubbles
Adarsh Kumar, Bahni Ray, Gautam Biswas
Abstract
In this study, the coalescence dynamics of two unequal sized vertically inline bubbles rising in a liquid column have been investigated using the coupled level-set and volume-of-fluid (CLSVOF) method. A wide range of bubble radius ratios of trailing bubble and leading bubble (0.25≤R≤2.0) and separation distances between the bubbles (2.5≤S≤3.5) have been deployed to investigate the evolution of the bubble wakes and bubble shapes. It is discovered that the coalescence time increases with R, the maxima being around 0.75≤R≤1, and then it decreases. With the increase in S, the coalescence time gradually increases. The existence of a pair of counter-rotating vortex rings has been observed between the bubbles, which are seen to accelerate the bubble coalescence process. For the present range of R and S, we show a regime map with four distinct coalescence pathways: coalescence with liquid entrapment, coalescence without liquid entrapment, penetration of the leading bubble, and premature splitting of the trailing bubble.