Genesis of an asymmetric sectorial wrap of air from a Taylor bubble upon facing concentric annular obstruction in a stagnant kerosene column is investigated. Careful observations are reported from processed images taken using high speed camera and with finite volume based simulations. The interfacial reconstruction of a Taylor bubble is completed through six distinct stages, namely, plateau formation, doughnut shape bypass of obstruction followed by nucleation, preferential rise, retraction of the lagging lobe and subsequent thread formation, consumption of thread including bubble segment stage, and finally the manifestation of the annular bubble before rising as steady annular sectorial wrap. Analysis of experimental observations related to interfacial rise and kinematic estimation from numerical study is presented in support of claims related to different transformation stages. A close similarity has also been reported between the stages involved in the interfacial reconstruction process and classical Rayleigh–Taylor instability.

This present work reports results of an experimental campaign in a 20 mm internal diameter tube to comprehend the interfacial evolution of a fully developed Taylor bubble to an annular bubble at the inception of an annulus. The phenomenon has been observed by using a high speed photography camera and has been further analyzed by using image processing tools. Interfacial evolution is found to be a complex phenomenon with various physics rich processes occurring simultaneously in six stages, namely, retardation of fully developed Taylor bubble, plateau formation, doughnut shape formation and nucleation of lobes, preferential rise of leading lobe and retraction of lagging lobe, thread formation of lagging lobe, and finally, manifestation of an annular bubble. Effects of fluid viscosity and eccentricity on hydrodynamics features, such as annular bubble rise velocity, film thickness, nose shape, and reacceleration of the annular bubble are investigated in detail.

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The bypass of an air bubble through a liquid−liquid interface may produce rich fluidic physics. Air injection is a passive technique to mix the contents of the two separated fluids and provides an effective heat and mass transfer intensification by increasing the interfacial area between them. Entrainment of heavier fluid into the lighter fluid at atmospheric and isothermal conditions has been simulated by using the VOF (volume of fluid) technique mimicking a Taylor bubble bypass through a horizontal liquid−liquid interface of water and polydimethylsiloxane (PDMS) solution. The migration of a Taylor bubble across the interface is completed through five different stages, namely, approach, encapsulation, de-encapsulation, entrainment, and detrainment. The bubble kinematics, entrained water volume, microdroplets formation, and film thinning characteristics have been studied in detail. The marginal pinch-off mechanism for the rupturing of the entrapped water film has been observed due to the presence of the surface tension gradient. The film thinning initially occurs due to the domination of gravitational force and eventually due to capillary force after the entrapped film thickness achieves capillary length scale, δ crit ∼ (σ/(ρg)) 1/2 . The entrapped water film shrinks over the interface of the Taylor bubble to generate the water microdroplets in the PDMS solution. The entrained height and volume of the water column grows quadratically with time.

In this paper, physical properties and flow properties of fly ash collected from seven fields of Electro-Static precipitator (ESP) hoppers of a coal fired thermal power plant have been investigated by using Powder Flow Tester operating based on Jenike's methodology. It was experimentally observed that the fly ash from different ESP hoppers have different flow properties. Various powder flow properties, such as cohesion, unconfined yield strength, angle of internal friction and wall friction angle were found to have power law variation with median particle size. Critical particle size, which caused a change in the flow properties of fly ash from cohesive to easy flowing, was experimentally evaluated and validated. Hopper half angle and critical outlet opening trends were determined for different fly ash samples to achieve mass flow condition for discharge. Additionally, two power law models were also developed for estimating hopper half angle and critical outlet openings using powder flow properties.