Computational Studies Of Electrohydrodynamics Of Liquid Drops In Ac Electric Fields
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| Author | : Md. Abdul Halim |
| Publisher | : |
| Total Pages | : 406 |
| Release | : 2013 |
| Genre | : |
| ISBN | : |
Management of bubbles, drops, and solid particles is a major task in many industrial processes. For almost all conventional applications, the gravitational force is predominantly used to control and manipulate their motion. In the cases where the gravitational force can no longer serve the purpose, particle control by electric field is a promising alternative. Thus, the electrohydrodynamic phenomenon, which deals with the interaction of fluid flow and electric field, is being studied in many physical, chemical, and engineering disciplines. Some of the prominent applications are microelectromechanical devices, enhancement of heat and mass transfer, and electroseparation devices (electrophoresis units, electrodialysis cells, and electrically driven desalters). In this thesis, the dynamics of drops suspended in AC electric fields were studied using Direct Numerical Simulations (DNS). The Navier-Stokes equation and the electrostatic equation were solved for the fluid inside and outside the drop. Several sets of simulations were performed concerning the dynamics of a single drop. The single bubble simulations captured the transient behavior of the drop, flow, and the electric field toward the quasi-steady state. Low surface tension drops readily deformed to oblate or prolate shapes while drops having high surface tension remained circular or went through rebound before reaching a quasi-steady state. The multibubble simulations showed the significance of the relative magnitude of the conductivity ratio (R) and the permittivity ratio (S), of the fluid drop to the ambient fluid, in the microstructure formation of the drops. When S>R, the drops tended to deform to oblate shapes and accumulate in the middle of the domain. For S The multibubble simulations showed the significance of the relative magnitude of the conductivity ratio (R) and the permittivity ratio (S), of the fluid drop to the ambient fluid, in the microstructure formation of the drops. When S>R, the drops tended to deform to oblate shapes and accumulate in the middle of the domain. For S
| Author | : Alireza Razeghi |
| Publisher | : |
| Total Pages | : 0 |
| Release | : 2023 |
| Genre | : Drops |
| ISBN | : |
In this dissertation, Direct Numerical Simulations are used to study the effect of the electric field on (1) superimposed liquids and (2) liquid drops. The governing equations are solved using a front tracking/finite method algorithm in conjunction with Taylor-Melcher leaky dielectric model to account for the electric force. In the first problem, the electric-driven instability of the interface separating two fluids is studied, where a light fluid overlays a heavier fluid. The goal is to explore the effect of the ratio of the dielectric properties on the growth of the instability and the electric-field driven fluid flow. It is shown that depending on the ratio of the dielectric properties, the interface deforms to a conic shape and settles to a steady state, or becomes needle-shape and grows indefinitely, until it is stopped by the electrode. In the second problem, two topics of interest are studied that have been less explored; namely, the interactions of a liquid drop with an electrode wall, and interactions of the drop pairs. It is shown that depending on the ratio of the electrical properties (i.e., permittivity and conductivity ratios), the drops will be attracted toward the electrode or will move away from it. The computations are carried out in three- and two-dimensional settings, as well as in an axisymmetric setting. In addition to the drop electrical properties, the initial distance from the electrode affects the drop response to the electric field, such that the drop closer to the electrode gains higher acceleration to move toward or away from the electrode. For the interactions of the drop pairs, the results of this study show that the critical angle, at which the sign of the radial velocity of the drop changes, is different for two- and three-dimensional systems. It is found that the drops may attract or repel each other, depending on their electrical properties or initial orientations. Furthermore, due to the existence of the critical angle, the drops may repel each other at early times, and then attract under special circumstances. As part of this study, an analytical solution is developed for two-dimensional systems to predict binary interactions of drops qualitatively, in a fast and inexpensive way. The analytical model is comprised of two parts; (i) the velocity derived from the dielectrophretic force of the drops, and (ii) the electrohydrodynamic flow due to mismatch between the electrical properties of the drops and the ambient fluid. Comparison of the analytical solution with that for a drop in a three-dimensional setting shows that there are quantitative differences between the two for the various dependent parameters of interest, such as the critical angle and the degree of the deformation.
| Author | : Antonio Castellanos |
| Publisher | : Springer |
| Total Pages | : 371 |
| Release | : 2014-05-04 |
| Genre | : Technology & Engineering |
| ISBN | : 3709125227 |
The aim of this book is to provide, both the non-specialist and the specialist in EHD, with the ability to extract meaningful information from his/her experimental data and acquire a good physical understanding, by applying the ideas presented in this book. In addition to providing the scientific background, it is also intended to take the reader to the frontiers of research in this field, so they may go, without effort, into the specialized literature. This book may be considered as complementary to the excellent treatment of EHD made in the classical book "Continuum Electromechanics” by Melcher, in that care has been taken to avoid overlapping of the subjects. In case a topic is treated in both texts, the results presented in the book by Melcher serve as an introduction to the more advanced treatment presented in this book.
| Author | : Debasish Das |
| Publisher | : |
| Total Pages | : 200 |
| Release | : 2016 |
| Genre | : |
| ISBN | : |
The dynamics of dielectric rigid particles and liquid drops suspended in another liquid medium and subject to a uniform DC electric field, the study of which forms the field of electrohydrodynamics (EHD), has fascinated scientists for decades. This phenomena is described by the much celebrated Melcher-Taylor leaky dielectric model. The model hypothesises development of interfacial charge on the application of an electric field and prescribes a balance between transient charge, jump in normal Ohmic currents due to finite conductivities of the medium and charge convection arising from interfacial velocity. While there have been numerous studies on the dynamics of particles and drops more conducting than the surrounding liquid medium, weakly conducting particles and drops in strong electric fields, known to undergo symmetry-breaking bifurcations leading to steady rotation known as Quincke electrorotation has received much less attention. Recent experiments have reported a decrease in the effective viscosity of particle under Quincke rotation, thereby providing a means to tune the rheological properties of these suspensions. However, existing models based on an isolated particle, valid for dilute suspension, have been shown to be inaccurate as the density of particles increases. Motivated to resolve these discrepancies, we develop a theoretical model to account for electrohydrodynamic interactions between a pair of spherical particles. We then turn our attention to many particles free to roll on an electrode due to Quincke rotation. Using numerical simulations, we show that electrohydrodynamic interactions between particles give rise to collective motion of these colloidal suspensions. We find emergence of a polar liquid state with large vortical structure in circular confinement. Finally, we address the problem of electrohydrodynamics of deformable liquid drops, first studied by Taylor in 1966. We develop a transient small deformation theory for axisymmetric drops while including the nonlinear charge convection term neglected by previous researchers. We also use numerical simulations based on a novel three-dimensional boundary element method to capture large deformations. These simulations are the first to capture Quincke rotation due to inclusion of the nonlinear charge convection term and show excellent agreement with existing experimental data and theoretical predictions in the small deformation regime.
| Author | : Alejandro Agustin Carderera de Diego |
| Publisher | : |
| Total Pages | : 166 |
| Release | : 2016 |
| Genre | : |
| ISBN | : |
Electrohydrodynamics is the study of the interaction between fluids and electric fields, and is used to model phenomena like fuel atomization or the mixing of multiphase flows under the influence of electric fields. Increasing interest is being placed in using electric fields to vary multiphase behaviour, one example is combustion processes, where finer droplets and wider sprays are created to increase engine efficiency. Another example can be seen in the pharmaceutical industry, where micro-encapsulation of compounds is achieved through the use of electrified coaxial liquid jets. In this work, the Ghost Fluid Method (GFM), and the Continuum Surface Force (CSF) approach will be used to discretize the electric potential Poisson equation for multiphase problems with arbitrary interfaces and discontinuous physical properties. A new scheme has also been derived to solve this problem, in the Finite Volume (FV) framework, and an extensive error analysis has been carried out to gauge the accuracy and properties of these schemes. These tools, coupled with NGA, the Computational Fluid Dynamics (CFD) code used in Dr. Olivier Desjardins' research group will allow the study of, among others, the two phase mixing of two dielectric liquids under the influence of an electric field, of interest to the chemical engineering industry, where an alternative non-mechanical way of mixing corrosive liquids is sought out, or the atomization of drops during fuel injection when an electric field is applied.
| Author | : |
| Publisher | : |
| Total Pages | : 494 |
| Release | : 1994 |
| Genre | : Fluid dynamics (Space environment) |
| ISBN | : |
| Author | : Marrivada Nanchara Reddy |
| Publisher | : |
| Total Pages | : 152 |
| Release | : 2008 |
| Genre | : |
| ISBN | : |
Management of bubbles/drops, and solid particles is a major task in many industrial processes. For almost all conventional applications, the gravitational force is predominantly used to control and manipulate their motion. In the cases where the gravitational force can no longer serve the purpose, particle control by electric field is a promising alternative. Thus, the electrohydrodynamic phenomenon, which deals with the interaction of fluid flow and electric field, is being studied in many physical, chemical, and engineering disciplines. Some of the prominent applications are microelectromechanical devices, enhancement of heat and mass transfer, and electroseparation devices (electrophoresis units, electrodialysis cells, and electrically driven desalters). In this thesis, the dynamics of drops suspended in an electric field were studied using Direct Numerical Simulations (DNS). The Navier-Stokes equation and the electrostatic equation were solved for the fluid inside and outside the drop. Several sets of simulations were performed concerning the dynamics of a single drop. The single bubble simulations captured the transient behavior of the drop, flow, and the electric field toward the steady state. Low surface tension drops readily deformed to oblate or prolate shapes while drops having high surface tension remained circular or went through rebound before reaching a steady state. The multibubble simulations showed the significance of the relative magnitude of the conductivity ratio (R) and the permittivity ratio (S), of the fluid drop to the ambient fluid, in the microstructure formation of the drops. When S > R , the drops tended to deform to oblate shapes and accumulate in the middle of the domain. For S
| Author | : |
| Publisher | : |
| Total Pages | : 144 |
| Release | : 1965 |
| Genre | : Capillarity |
| ISBN | : |
| Author | : Royal Society (Great Britain) |
| Publisher | : |
| Total Pages | : 618 |
| Release | : 1973 |
| Genre | : Electronic journals |
| ISBN | : |
| Author | : Núria Romero Herreros |
| Publisher | : |
| Total Pages | : |
| Release | : 2014 |
| Genre | : |
| ISBN | : |
The electrowetting effect has emerged as an important research topic in recent years. Manipulation of droplets by electric fields has been extensively studied employing different setups, the most common being the configuration in which the electric field is created inside the droplet. However, such a configuration has been mostly employed using conductive liquids, whereas non-conductive droplets have been barely tested under the effect of an electric field using this setup. On the other hand, the influence of an electric field on the shape of a droplet has also been of considerable interest using an alternative configuration in which the electric field is applied between two electrodes with no contact with the drop – the Taylor cone configuration. However, the effects observed employing this last setup are rather different to those obtained using the aforementioned design. While the most important effect in those experiments in which the electric field is created inside the drop is the reduction of the contact angle, the main effect found using the second configuration is the droplet elongation in the electric field direction. In order to demonstrate if dielectric and almost perfectly wetting liquid droplets are affected in the same way as other fluids already tested, the effect of an electric field on the shape of an HFE-7500 droplet has been examined under two different experimental setups by means of interferometric techniques. For the setup where the internal electric field is created, no statistically relevant reduction was measured. Nevertheless, shape deviations have been found at a certain distance of the wire through which the electric field is applied. Moreover, the existence of such deviations depends strongly on the AC frequency. Regarding the second design, it should be mentioned that the initial parallel plate design was working correctly for water+salt droplets. However, no remarkable effects were observed applying strong electric fields of up to 10 kV/cm on HFE-7500 droplets. With the goal of increasing the field strength, two improvised configurations of a metal ring and a needle as a counter-electrodes have also been implemented. In these cases, a strong non-uniform electric field was created which did lead to shape changes of the droplets.
