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Seminar on "Dynamic evolution of gas-liquid interfaces during bubble bursting, bubble coalescence and entrainment at the free surface by rotary rollers" - 28 May 2018

Date and Venue Information:
28 May 2018, Seminar Hall, 11:00 AM, Department of Mechanical Engineering

Title of Seminar:
"Dynamic evolution of gas-liquid interfaces during bubble bursting, bubble coalescence and entrainment at the free surface by rotary rollers" by Basanta Kumar Rana

Abstract
Efforts have been made in order to understand the interaction of interfaces in various gas-liquid two-phase flow phenomena. Attention has been focused particularly to the bursting of Taylor bubble at the free surface inside a conduit, the mutual interplay of bubbles evolving from neighbouring orifices and entrainment of air inside stratified liquid due to rotary motion of a cylinder.
Experiments have been performed to investigate collapse dynamics of axisymmetric and asymmetric Taylor bubble at the free surface of different liquids inside vertical and inclined tubes. Retraction of cap film and dewetting of wall adhered annular film are found out to be the main fluidic mechanisms behind bursting of Taylor bubble. Dissimilar retraction rate in different azimuthal directions from puncture point and drainage of wedge shaped asymmetric liquid film adhered to wall are the characteristics of Taylor bubble collapse in the inclined tube. Using scale analysis, both retraction and dewetting periods are predicted and matched satisfactorily with experimental observations. Numerical simulations are performed to understand the flow dynamics around retraction and drainage in both vertical and inclined liquid columns. Volume of fluid based interface tracking is used to capture the thin films in adaptive finite volume framework.
 Interactions among three bubbles evolving from inline orifices are observed using high speed imaging. Bubbles from equispaced orifices reveal symmetric liquid drainage and gaseous interconnection leading unification before pinch off. Asymmetric arrangement of orifices in terms of spacing and diameter showed several interesting interfacial structures resulting in partial coalescence and non-coalescence. Conception of these different merging patterns is developed from numerical investigations for binary and tertiary interactions. A regime map is proposed to separately identify different interactions between bubbles. 
Experimental observation and supporting numerical efforts have been made to investigate the entrainment of gas inside liquid due to rotary motion of a horizontal cylinder submerged up to its centre. Liquid wrap around the cylinder in receding end of the cylinder and gaseous cusp in the advancing one characterizes rotary entrainment in air-water combination. Numerical simulations reveal higher azimuthal climb of liquid and gaseous film entrainment originating from cusp for more viscous liquid and air interaction. Using scale analysis, it has been shown that viscosity plays a major role in deciding the azimuthal wrap thickness.
 
Brief Profile:
Dr. Basanta Kumar Rana obtained doctoral degree in the area of multi-phase flows from IIT Kharagpur in 2018. He obtained M.Tech in Fluids and Thermal Engineering from IIT Guwahati in 2013. His research interests are in the areas of Multiphase flow, two phase flow, Gas-liquid and liquid-liquid flow, Computational Fluid Dynamics, Heat transfer, Natural and mixed convection flow, Interface tracking (VOF method).
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