Author: Nehzat EmamyPublisher:
ISBN:
Category :
Languages : en
Pages : 165
Book Description
Numerical Simulation of Deformation of a Droplet in a Stationary Electric Field Using DG
Author: Nehzat EmamyNumerical Simulation of Time-dependent Droplet Deformation in an Electric Field
Author: Graeme M. SupeenePublisher:
ISBN:
Category : Drops
Languages : en
Pages : 298
Book Description
Numerical Modeling of Deformation, Oscillation, Spreading and Collision Characteristics of Droplets in an Electric Field
Author: Osameh GhazianPublisher:
ISBN:
Category :
Languages : en
Pages :
Book Description
Electric field induced flows, or electrohydrodynamics (EHD), have been promising in many fast-growing technologies, where droplet movement and deformation can be controlled to enhance heat transfer and mass transport. Several complex EHD problems existing in many applications were investigated in this thesis. Firstly, this thesis presents the results of numerical simulations of the deformation, oscillation and breakup of a weakly conducting droplet suspended in an ambient medium with higher conductivity. It is the first time that the deformation of such a droplet was investigated numerically in a 3D configuration. We have determined three types of behavior for the droplets, which are less conducting than ambient fluid: 1) oblate deformation (which can be predicted from the small perturbation theory), 2) oscillatory oblate-prolate deformation and 3) breakup of the droplet. Secondly, a numerical study of droplet oscillation placed on different hydrophobic surfaces under the effect of applied AC voltage including the effect of ambient gas was investigated. The presented algorithm could reproduce droplet oscillations on a surface considering different contact angles. It has been found that the resonance frequency of the water droplet depends on the surface property of the hydrophobic materials and the electrostatic force. Thirdly, a new design of an electrowetting mixer using the rotating electric field was proposed which offers a new method to effectively mix two droplets over a different range of AC frequencies. Two regimes were observed for droplet coalescence: 1) coalescence due to the high droplet deformation, 2) coalescence due to the interaction of electrically induced dipoles. Fourthly, the spreading and retraction control of millimetric water droplets impacting on dry surfaces have been investigated to examine the effect of the surface charge density and electric field intensity. The effect of the surface charge on the spreading of droplets placed gently on surfaces was investigated in the first part. It was found that the maximum spreading diameter increases with an increasing charge. In the second part, the impact of a droplet on a ground electrode was considered. It was also found that in order to keep the maximum diameter after the impact, less charge is needed for surfaces with lower contact angle. Finally, the interaction between two identical charged droplets was investigated numerically. The effects of the impact velocity, drop size ratio and electric charge on the behavior of the combined droplet were investigated. It was shown that two conducting droplets carrying charges of the same polarity under some conditions may be electrically attracted. The formation of charged daughter droplets has been investigated and it was found that the number of the satellite droplets after collision appears to increase with an increase in the droplet charge.
Electro-deformation of a Moving Boundary
Author: Herve NganguiaPublisher:
ISBN:
Category :
Languages : en
Pages : 260
Book Description
This dissertation focuses on the deformation of a viscous drop and a vesicle immersed in a (leaky) dielectric fluid under an electric field. A number of mathematical tools, both analytical and numerical, are developed for these investigations. The dissertation is divided into three parts. First, a large-deformation model is developed to capture the equilibrium deformation of a viscous spheroidal drop covered with non-diffusing insoluble surfactant under a uniform direct current (DC) electric field. The large- deformation model predicts the dependence of equilibrium spheroidal drop shape on the permittivity ratio, conductivity ratio, surfactant coverage, and the elasticity number. Results from the model are carefully compared against the small-deformation (quasispherical) analysis, experimental data and numerical simulation results in the literature. Moreover, surfactant effects, such as tip stretching and surface dilution effects, are greatly amplified at large surfactant coverage and high electric capillary number. These effects are well captured by the spheroidal model, but cannot be described in the second-order small-deformation theory. The large-deformation spheroidal model is then extended to study the equilibrium deformation of a giant unilamellar vesicle (GUV) under an alternating current (AC) electric field. The vesicle membrane is modeled as a thin capacitive spheroidal shell and the equilibrium vesicle shape is computed from balancing the mechanical forces between the fluid, the membrane and the imposed electric field. Detailed comparison against both experiments and small-deformation theory shows that the spheroidal model gives better agreement with experiments in terms of the dependence on fluid conductivity ratio, electric field strength and frequency, and vesicle size. Asymptotic analysis is conducted to compute the crossover frequency where a prolate vesicle crosses over to an oblate shape, and comparisons show the spheroidal model gives better agreement with experimental observations. Finally, a numerical scheme based on immersed interface method for two-phase fluids is developed to simulate the time-dependent dynamics of an axisymmetric drop in an electric field. The second-order immersed interface method is applied to solving both the fluid velocity field and the electric field. To date this has not been done before in the literature. Detailed numerical studies on this new numerical scheme shows numerical convergence and good agreement with the large-deformation model. Dynamics of an axisymmetric viscous drop under an electric field is being simulated using this novel numerical code.
Numerical Modeling of Flow and Deformations Induced in a Droplet Subjected to Alternating Electric Field
Author: Nithin S. PanickerPublisher:
ISBN:
Category :
Languages : en
Pages : 82
Book Description
Numerical investigation of the flow in a drop of a dielectric fluid suspended in another immiscible dielectric fluid in the presence of an alternating electric field has been carried out. When an electric field is applied to a drop of a dielectric fluid, the electric field induces stresses at the fluid interface. The normal stresses deform the drop and the tangential stresses produce a circulatory motion inside and outside the drop. Such electrical field induced flow can lead to significant enhancement of heat or mass transfer to from the drop. A stream function-vorticity approach with a finite volume formulation is adopted to numerically determine the unsteady flow field in the continuous and the dispersed phases. The volume of fluid (VOF) method is used to track the phase boundary and to predict the transient drop shape deformations for a range of capillary numbers. A new VOF formulation with Continuum Surface Force model has been derived and implemented to account for both the tangential and the normal electrical stresses present at the phase interface. Results show that the extent of drop deformation increases with capillary number and the strength of the electric field. By tracking Lagrangian fluid particles inside the deforming droplet, it is seen that the changing flow patterns due to drop deformation lead to significant fluid mixing inside the droplet. Earlier studies available in the literature neglect drop deformations and may significantly underestimate the heat/mass transfer enhancement in the presence of an alternating electric field.
Numerical Simulation of Droplet Deformation in Convective Flows
Author: Zheng-Tao DengNumerical Simulation of Droplet-deformation by a Level Set Approach with Surface Tension
Author: Roberto CroceNumerical Simulation of Droplet Deformation Using Spectral Element Method
Author: Yu ZhengNumerical Simulation of Bubble and Droplet Deformation by a Level Set Approach with Surface Tension in Three Dimensions
Author: Roberto CroceIntensification of Liquid–Liquid Processes
Author: Laurence R. WeatherleyPublisher: Cambridge University Press
ISBN: 1108421016
Category : Mathematics
Languages : en
Pages : 379
Book Description
Explore and review novel techniques for intensifying transport and reaction in liquid-liquid and related systems with this essential toolkit. Topics include discussion of the principles of process intensification, the nexus between process intensification and sustainable engineering, and the fundamentals of liquid-liquid contacting, from an expert with over forty-five years' experience in the field. Providing promising directions for investment and for new research in process intensification, in addition to a unique review of the fundamentals of the topic, this book is the perfect guide for senior undergraduate students, graduate students, developers, and research staff in chemical engineering and biochemical engineering.