رديابي ذرات باردار در جريان غيرقابل تراكم در ميدان الكتريكي

چكيده انگليسي :

AbstractIn this investigation the motion of charged particles for incompressible flow in electrical field has beeninvestigated Two applications of this subject have been simulated and compared with experimental results The first one is a simulation model for electrets filter made of split type fiber This simulation has beendeveloped to study the filtration efficiency The filter was assumed to be composed of rectangular fibersarranged in staggered array field Single fiber efficiencies under various filtration conditions werecalculated and compared with results obtained from semi empirical expressions derived from experimentalresults Firstly charged and neutral particle collections in an electric filter composed of rectangular split type fibers are simulated Both the flow field and the electric field around the fiber are numericallydetermined All the major collection mechanisms mechanical and electrostatic have been coupled in thedifferential equation of particle motion The single fiber collection efficiency is obtained from tracing andrecording the particle trajectories Simulations have been conducted under wide range of filtrationconditions and results are compared with those obtained from Kanaoka et al The second one is thenumerical simulation of electrostatic powder painting The purpose of this study was to understand the gasand particle flow fields inside a coating booth under given operating conditions and the effect of particlesizes on its trajectories The continuous gas flow was calculated by solving Navier Stokes equationsincluding the standard k turbulence model and the discrete phase was modeled based on the Langrangianapproach In both cases the flow field and the collection mechanisms were determined by Fluent software The numerical model for the simulations of the gas and solid particle flows in a powder coating system waspresented and its results were compared with the experimental data It was found that the numerical modelpredicts quite accurately the particle velocities and average particle diameter at different locations inside thecoating booth when there was no electrostatic field The numerical results showed similar effect of theelectrostatic field on the flow field as that from experimental results The differences between numericalresults and experimental data for the case of with the coating part and with electrostatic field are mostprobably due to the assumption of constant charge to mass ratio and spherical shape of particles for thisstudy Thus it should be important to numerically resolve particle charging using unsteady particle trackingor consider variable particle charge based on its diameter In general the presented simplified modelappears useful for carrying out parametric studies considering different monosize powders The gas andparticle flow fields could be understood by measuring the particle velocities and diameters at variouslocations inside the booth Near the spray gun region the aerodynamic force is dominant and so the particlestravel under its effect Moving away from the spray gun the electrostatic and the gravity force becomedominant The bigger particles tend to accumulate near the bottom of the coating booth and fine particlesremain suspended with the gas flow for the longer time and finally being carried away through the suctionhole The electrostatic force is in the axial direction of spray and acts as an additional source to theparticles momentum Thus the electrostatic force plays an important role to increase the particle transferefficiency In addition it affects the particle trajectories and expands it in the radial direction and finallyconcentrating on the target edges along the field lines Key wordsParticle gas flow numerical simulation electret filter powder coating Isfahan University of Technology Department of Mechanical Engineering Charged particle tracking on uncompressable flow on electrical field A Thesis Submitted in partial fulfillment of the requirements

محمدزاده، اميرحسين

رديابي ذرات باردار در جريان غيرقابل تراكم در ميدان الكتريكي

فيلتر الكترواستاتيك , رنگ پاشي الكترو استاتيك