شبيه سازي عددي ديناميك قطره تحت اثر ميدان الكتريكي يكنواخت

چكيده انگليسي :

Numerical Simulation of Droplet Dynamics in the Presence of Uniform Electric Field Hamed Paknemat h Paknemat@me iut ac ir Date of Submission 2011 05 2 Department of Mechanical Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language FarsiSupervisor AhmadReza Pishevar apishe@cc iut ac irAbstractElectrohydrodynamics EHD is a branch of science which deals with the coupling of hydrodynamics andelectrostatics An extensive amount of research has been done by many different researchers on the deformationof a fluid drop in a second immiscible fluid under the influence of an applied electric field Electric dropdeformation has a wide variety of applications Knowledge of this phenomenon is useful in the study ofaerosols in the enhancement of heat or mass transfer between phases coalescence ink jet printing removalprocess electrowetting and many other industrial applications In this study the suspended drop system is analyzed numerically in terms of its dynamic behavior Twodifferent electric models are applied in order to take into account the effects of the electric eld electric chargesand electrical properties of liquids Droplets without net charges but nite electrical conductivity are simulatedusing a leaky dielectric model Perfect dielectric model is used for the drops of electrically isolating uid Adroplet with no net charge and different physical properties than the surrounding uid polarizes when placed ina uniform electric eld As a result the electric stress undergoes a jump across the interface and deforms thedrop If the uids are perfect dielectrics there are no free charges and the electric stress discontinuity has only anormal component At steady state it is balanced by interfacial tension the drop adopts an equilibrium shape ofa prolate ellipsoid and both internal and external uids are motionless Slightly conducting materials behavedramatically differently from ideal dielectrics due to the presence of mobile charges Charges carried byconduction accumulate at interfaces The electric eld acting on these surface charges creates a tangential stress not present in the perfect dielectric case which drags the uid into motion The direction of the resultingstraining ow about the drop depends on the charge distribution along the interface and can deform the drop intoan oblate ellipsoid In order to simulate the dynamic of a 2D axisymmetric droplet in an electric field in this study the level setmethod along with the ghost fluid method are used In recent years some sharp methods have been proposedwhich attempted to treat physical properties at the interface in a sharp way The ghost uid method GFM wasproposed for two phase compressible inviscid ows which can maintain the discontinuous properties at theinterface without any arti cial smoothing It has been shown that the sharp pressure jump conditions were wellpreserved The incompressible Navier stokes equation has been employed for modeling the internal and externalfluid flow of the droplet In addition to calculate the electric potential in the entire domain the Poisson equationwith discontinuous coefficients has been solved using the ghost fluid method The electrically induced forcesbetween two fluids are incorporated in the interfacial stress condition through a sharp manner The results showthe capability of the method in modeling the droplet deformation In addition the results obtained from the leaky dielectric model and perfect dielectric model are validatedsystematically against the results of theoretical analysis the available experimental data and the simulations byother researchers The results obtained from the drop deformation simulation under a uniform electric field show that thepresent numerical method is reasonably accurate and promising The intrinsic potency of this method in dealingwith topological changes enables us to study problems involving break up or coalescence processes such as filmboiling or emulsion stability Keywords Electrohydro

پاك نعمت، حامد

شبيه سازي عددي ديناميك قطره تحت اثر ميدان الكتريكي يكنواخت

جريان دوفازي , لول ست , روش سيال مجازي , الكتروهيدروديناميك , الكترواستاتيك