بررسي عددي الكتروهيدروديناميك جت مايع تحت اثر ميدان الكتريكي يكنواخت به روش المان مرزي

چكيده انگليسي :

Numerical Investigation of Electrohydrodynamic Liquid Jet under Uniform Electric Field by Boundary Element Method Ali Reza Hashemi alireza hashemi@me iut ac ir Date of Submission 2016 01 16 Department of Mechanical Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language FarsiSupervisor Ahmad Reza Pishevar apishe@cc iut ac irAbstract Electrospinning is a process in which solid fibers are produced from a polymeric fluid streamdelivered through a millimeter scale nozzle The aim of this research is to study the effects ofprominent parameters in terms of non dimensional numbers on the process with and withoutcentrifugal force For this purpose a numerical model is developed to solve governing equations andthe obtained results are validated with the existing numerical and experimental results In this model the hydrodynamics equations are simplified by a perturbation method and the boundary integralmethod is used to solve the Electrostatic equations Then by forcing the boundary conditions at theinterfaces for the stresses the two set of equations are coupled The governing EHD equations arediscretized via a second order central finite difference method and the resulting system of equation issolved by using a Newton like iterative method In this study also the electrical behavior of system isconsidered as the leaky dielectric and dielectric fluid models for the liquid jet and surrounding fluid respectively For the leaky dielectric model low conductivity of the fluid causes the formation a thinlayer near the interface of the electric charges Here we assume that the charge redistribution occursinstantly and a static model for charges is acceptable Also the presence of nozzle in between of twoelectrodes makes a non uniform electric field in the vicinity of the nozzle and consequently increasesthe magnitude of the electric field In some previous simulations the nozzle geometry and its effect onthe external electric field were included in the simulations However in this study the nozzle effect isautomatically included by applying proper boundary condition at the nozzle R 0 1 in the BEMformulation Moreover an analytical method is used to remove the singularity at the axisymmetricboundary Finally the method is validated against several benchmark problems Then the method isused to predict the reduction in the jet radius along the axis of the jet jet elongation and the jet centerline deviation in the horizontal plane when the dimensionless numbers such as Weber Reynolds Farad Rossby Beta and aspect ratio are changed Results shows that in electrospinning the Weberand Beta dimensionless numbers are very effective in the jet radius reduction and comparing thepresent results with the other numerical and experimental results confirms that the static model forelectric charges is accurate only at low volume flow rate and high applied electric field In electro centrifuge spinning the jet elongation is severely affected by Rossby and aspect ratio By increasingReynolds Rossby Beta and aspect ratio and reducing Weber dimensionless numbers the deviation ofjet center line from a straight line is increased Also at high rotational speeds 1000 theprocess is only controlled by the centrifugal force and other electric parameters represented by Beta inthe momentum equation have little influence on the results Keywords Liquid jet Electric Leaky dielectric Perturbation Boundary integral Centrifuge

هاشمي، عليرضا

بررسي عددي الكتروهيدروديناميك جت مايع تحت اثر ميدان الكتريكي يكنواخت به روش المان مرزي

رسانايي ناچيز , اختلالي , انتگرال مرزي , گريز از مركز