Numerical Simulation of Time-dependent Droplet Deformation in an Electric Field PDF Download
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Author: Graeme M. Supeene
Publisher:
ISBN:
Category : Drops
Languages : en
Pages : 298
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Author: Graeme M. Supeene
Publisher:
ISBN:
Category : Drops
Languages : en
Pages : 298
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Author: Nehzat Emamy
Publisher:
ISBN:
Category :
Languages : en
Pages : 165
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Author: Osameh Ghazian
Publisher:
ISBN:
Category :
Languages : en
Pages :
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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.
Author: Zheng-Tao Deng
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: Herve Nganguia
Publisher:
ISBN:
Category :
Languages : en
Pages : 260
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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.
Author: Kathrin Schulte
Publisher: Springer Nature
ISBN: 303109008X
Category : Drops
Languages : en
Pages : 372
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Book Description
This open access book presents the main results of the Collaborative Research Center SFB-TRR 75, which spanned the period from 2010 to 2022. Scientists from a variety of disciplines, ranging from thermodynamics, fluid mechanics, and electrical engineering to chemistry, mathematics, computer science, and visualization, worked together toward the overarching goal of SFB-TRR 75, to gain a deep physical understanding of fundamental droplet processes, especially those that occur under extreme ambient conditions. These are, for example, near critical thermodynamic conditions, processes at very low temperatures, under the influence of strong electric fields, or in situations with extreme gradients of boundary conditions. The fundamental understanding is a prerequisite for the prediction and optimisation of engineering systems with droplets and sprays, as well as for the prediction of droplet-related phenomena in nature. The book includes results from experimental investigations as well as new analytical and numerical descriptions on different spatial and temporal scales. The contents of the book have been organised according to methodological fundamentals, phenomena associated with free single drops, drop clusters and sprays, and drop and spray phenomena involving wall interactions.
Author: H. H. Chiu
Publisher:
ISBN:
Category : Deformations (Mechanics)
Languages : en
Pages : 68
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A time dependent analysis is made of the deformation of an initially spherical drop moving in an unbound fluid at low Reynolds number. It is found that the excitation of a particular mode of deformation, including simple deformation, oscillation, and unstable deformation, depends on the Reynolds number, Weber number, the ratios of the two fluid densities and viscosities. The result of an analysis in the limit of vanishing voscosities shows that the droplet vibrates. The characteristic frequency obtained in the present analysis agrees with that previously obtained by H. Lamb. For large viscosities a limiting analysis indicates that a droplet deforms asymptotically to the equilibrium shape predicted by T.D. Taylor and A. Acrivos. The characteristic time of the deformation for ethyl alcohol droplets of 20 to 80 micrometers in diameter vary approximately from 0.001 sec to 0.005 sec. The effects of increasing temperature and pressure, free stream velocity and the droplet size are examined numerically for the deformation of ethyl alcohol drops. The unstable modes of deformation are likely to be excited at Reynolds number and Weber number both greater than unity. (Author).
Author: Elmars Blums
Publisher: Walter de Gruyter
ISBN: 3110807351
Category : Science
Languages : en
Pages : 429
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Author: Roberto Croce
Publisher:
ISBN:
Category :
Languages : en
Pages : 25
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Author: Yu Zheng
Publisher:
ISBN:
Category : Algorithms
Languages : en
Pages : 432
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