UNDERSTANDING INTERFACIAL ENTRAINMENT PROCESSES AT ADIABATIC THREE-PHASE DOMAIN AND LIQUID-LIQUID BOILING

Abstract

Understanding interfacial entrainment at adiabatic liquid-liquid contact induced by a Taylor bubble and boiling at liquid-liquid interface is targeted in the present scope of the thesis. Entrainment of heavier fluid induced by a Taylor bubble into a lighter fluid at atmospheric and isothermal condition has been simulated using volume of fluid (VOF) framework. The migration of a Taylor bubble across the water-PDMS (poly dimethyl siloxane) interface is completed through approach, encapsulation, de-encapsulation, entrainment, and detrainment stages. The bubble kinematics, entrained water volume, micro-droplets formation, and film thinning characteristics have been identified. The pinch-off mechanism in the rupturing entrapped water film has been observed due to the presence of the surface tension gradient. The film thinning initially occurs due to dominant gravitational force and then eventually due to capillary force after the entrapped film thickness achieves capillary length scale, 𝛿𝑐𝑟𝑖𝑡 ~ √𝜎𝜌𝑔⁄ . The entrapped water film shrinks over the interface of the Taylor bubble to generate the water micro-droplets in the PDMS solution. Simulations showed that the entrained height and volume of the water column grows quadratically with time. To understand the effect of thermo-physical properties on the entrainment dynamics, simulations with multiple fluid combinations are carried out. Split or unified bypass of Taylor bubble is identified depending on liquid-liquid combinations. Higher amount of entrainment is observed for the case of unified bypass as compared to split bypass. Effects of varying viscosity and density ratios of heavier to lighter liquids, interfacial tension between liquids, bubble size, and the presence of trailing bubble on the entrainment dynamics have been evaluated. Entrainment of the heavier fluid decreases with decrease of heavier to lighter liquid viscosity ratio, interfacial tension, and the bubble size. Whereas the maximum entrained volume decreases with an increase in the density ratio. In the presence of a trailing bubble, entrainment is decreased significantly compared to the isolated Taylor bubble’s passage through the liquid-liquid interface.