Collision of two oblique liquid jets
Vatsal Sanjay, Anurag Soni
Over the last few decades there has been a substantial growth in the micro scale fluid manipulation in the field of clinical diagnosis and biomedical applications in order to cope with the growing demand of parallelization and automation of complex chemical processes. Among other techniques of small scale liquid handling, electro-wetting grabs considerably higher attentions due to its better controllability, low cost, high switching rate and precision. In electro wetting, the interfacial surface energy of a droplet is reduced by applying an external electric field. The reduction of the interfacial tension causes change in the contact angle with the solid substrate on which the droplet is resting. Our research goal is to understand the dynamics and to control liquids and their interfaces by electro-wetting ranging from molecular to macroscopic scales. We deal with both application as well as fundamental studies in the static and dynamic wetting of liquid droplet by electro static actuation. These studies include translation of liquid droplet on inclined surfaces by electro-wetting, controlling drop impact by electro-static actuation, understanding the flow dynamics during droplet coalescence propelled by electric field etc, in both theoretical as well as experimental approaches. We also perform molecular dynamic study to explore wetting behaviour of static as well as translating nano-droplets on charged solid surfaces. Our studies are practically relevant to several engineering and biomedical applications such as hot spot cooling of electronic chip, liquid lenses, electro wetting display, biomedical micro-mixtures etc.
Formation, evolution and collapse of interfaces are like breaking and making of interfaces in various phenomena of two phase flow. Collapse of a Taylor bubble inside a pipe at free surface for different fluid has been studied, both experimentally and numerically. In this case, one existing free surface breaks with generation of a new interface after bursting Taylor bubble.
This work deals with the process of evolution of bubbles from orifice mouth pair and their subsequent coalescence through the processes of approach, film drainage, contact and unification.
Deformation of interface occurs when a horizontal roller rotates in stratified liquid-liquid or gas-liquid layer. In this situation, the lighter fluid penetrates into the heavier fluid by deforming the existing interface between them.
In different phenomenon, the scale involved ranges from a few centimetres (like the jet the diameter) to fractions of millimetres (small droplets formed due to the atomization of a liquid jet). Traditional Volume of Fluid (VOF) approach requires huge computational resources. Currently, we are using Gerris-Particle along with Gerris-VOF to simulate cases with multi-length scales such as Bubble Entrainment due to plunging liquid jet impinged onto the liquid pool, kitchen sink vortex and events of necking and orificing during the co-current flow of two fluids in concentric streams. We have examined the Gerris-Particle source code (pdf) and are working on modifications necessary to simulate the cases of interest. We ultimately aim to develop an in-house hybrid code for tackling the multiple scales.
Presence of multiphase flows is very common in many industries such as chemical processing, petroleum and nuclear etc. These industries involves the transportation of fluids with different phases through a common pipeline such as gas/liquid flow in offshore natural gas industry or even sometimes the flow of two immiscible liquids. In case of stratified liquid – liquid flows the lighter and the heavier phases are located at top and bottom of the pipeline, separated by an interface, which can be smooth, wavy or the droplets of one phase might be present in other. The interface could be sharp or diffused, depending upon the fluid properties. In case of diffused interface the diffusion of one phase takes place in another phase, which leads to a thick stratified zone. This study is aimed to determine the shape of wavy interface experimentally and numerically for kerosene – water flow through straight horizontal pipes.
Pulsating loop heat pipes (PHP) are unique heat transfer devices capable of transferring substantial amount of thermal energy from a low temperature body to a high temperature one without requiring any active deriving agency or auxiliary power supply. Heat pipes works the same way as thermo syphon except wick-structure along the wall transports the condensate. Experiments were conducted in quartz two-loop CLPHP to visualize the flow behaviour. Heating section consists of furnace and condenser section consists of a condensing unit circulating water at desired conditions. Heat Input was gradually increased whereas condenser was maintained at constant conditions. At low heat flux, above the system threshold, movement in liquid slugs and vapor plugs starts. Pulsating movement transfers the heat, and heat transfer is generally low at the stage. With increase in heat input, pressure difference between condensing section and heating section increases and fluid tends to cross over the loop.
Boiling on Cylindrical Wires
Boiling around cylindrical wire is the most popular and simple design of hot surfaces for dissipation of heat. Due to interaction of multiple factors such as heat flux, wire geometry, inclination and neighbour interference, boiling around wire is still not understood fully from first principle. Knowledge from the present study will definitely help understanding the boiling heat transfer and its mutual dependence on different factors as well as impact on device design based on phase change heat transfer.
Bubble Dynamics of Adjacent Nucleation Sites
Chandan Swaroop Meena
Numerical simulation and experimental work to find out the bubble dynamics of adjacent nucleation sites to observe breaking and making of interfaces have been carried out. Volume of fluid based finite volume discretization is adapted. Re-entrant cavities of opening and different spacing are taken as a source of bubble generation in the present study.
Influence of Wettebility Gradient on Drop Motion
Prabh Pal Singh Seerha
Efforts are made to simulate behavior of droplet under different conditions like moving of droplet down the incline plane due to gravity and droplet translation against gravity due to wettebility gradient. For this simulation, we are using Large scale Atomic and Molecular Massively Parallel Simulator (LAMMPS) software.
Bubble Entrainment by Liquid Jet Impinged onto a Pool: Experimental Study
Full scale experiments have been carried out for characterization of entrained bubble cluster and region of entrainment due to plunging liquid jet impinged onto a liquid pool. Based on high speed image analysis and conductivity probe signals, entrainment pattern is examined for a wide range of jet velocity and diameter (10000<Re<50000). Our main focus has been to investigate the temporal and spatial variation in obtained interface. Alongside, a conductivity probe has also been used to examine the probabilistic presence of bubble at a given coordinate in the liquid pool.
Bubble Entrainment by Liquid Jet Impinged onto a Pool: Numerical Study
Numerical simulation of the observed phenomenon of bubble entrainment is carried out using volume of fluid (VOF) based interface tracking method of Gerris. Characterization of the region of pool affected by entrainment is also carried out. Triangular entrained region is found to be a three-dimensional cluster of bubble population continuously breaking and making with neighbors due to turbulent dispersion induced by jet. During entrainment, free surface of the pool shows undulations which subsequently releases droplets of different sizes around the jet. The trajectories of the droplets are driven by jet inertia and subsequent gravitational interactions.
Rolling and Orificing Phenomenon in Vertical Tubes
Parallel and counter flow of different phases through vertical tubes is very common in many adiabatic and non – adiabatic applications. On such application in which air and water flows through a vertical tube has been numerically investigated. Water flows through the annular space adjacent to the tube boundaries and air flows through the core of tube. Some of the simulation results reveal that an orifice like structure is formed by the liquid layer inside the tube at lower relative velocities between air and water; however this orifice breaks at higher relative velocities and subsequently leads to folding of liquid layer, called as rolling. Further efforts are also being made to critically examine the detachment and attachment of liquid droplets from its annular film.
Current research primarily involves computational investigations of Ferrofluid (FF) flow transport phenomenon such as interfacial disturbances (e.g. Rayleigh-Taylor instability, interface oscillations and magnetic-levitation) together with physical experiments. Small scale experiments, such as in Hele-Shaw cell, are designed for the same. Besides this, numerical modelling of magnetization relaxation time and flow vorticity effects in FFs is also under investigation. The investigations are based on an in-house developed numerical code with object-oriented features enabled for easy future developments of the computer program.
As a part of Bachelor thesis project, this project deals with compartmental fire in Railway bogeys in running condition. Finite volume based simulations are developed individually as also in interconnected array for A/C coach, Non-A/C coach, pantry car. Modelling is being done on flame and soot propagation for accidental fires with different possible sources of fire. Evacuation strategy, design changes and structural changes will be devised based on the study.
The project deals with molecular perspective of gas-liquid phase change and subsequent bubble formation. From fundamental physics, efforts will be made to understand molecular dispersion in boiling and formation of spherical bubbles as accumulation of loosely packed vapor molecules. Both film boiling and nucleate boiling from preferential sites will be investigated in this project and fundamental understanding of boiling heat transfer will be developed.
The project deals with the study of compartmental fire in multi-storied building through full-scale numerical simulation. Coupled finite difference and finite volume based open source solver, Fire Dynamics Simulator (FDS) is used for domain discretization and solution of governing equations. It aims at optimization of placement of air-conditioner, stairs and elevators for better access and evacuation from fire hazards. Soot flow pattern and flame contours are also observed for the considered cases. Placement of sprinklers is being accessed for different burning situations.
This project deals with the numerical simulation of Leidenfrost effect using finite volume method where a drop of liquid above certain temperature known as leidenfrost point levitates over a cushion of insulating vapor layer which prevents it from boiling. The challenge is to understand how the liquid behaves with varying conditions of temperature, volume of the droplet and structure of the surface on which the drop is kept along with other situations where an asymmetry in the solid/liquid contact is used to generate the self-propulsion of the liquid droplet. Once we understand the phenomenon of the drop levitation and propagation, we can then put this concept into further applications of micro-fluidics.