Numerical analysis of charged droplets size distribution in the electrostatic coating process: Effect of different operational conditions

Abstract

This paper presents a numerical performance evaluation of the electrostatic rotary bell sprayer (ERBS) with a particular focus on droplet charge, electric field, and ambient conditions through the implementation of a high-voltage control-ring field pattern effect into the fully turbulent airflow and by including the atomized droplets discrete phase. The simulation shows that the inclusion of droplet charging and electric field coupling, with different parametric values, significantly impacts the atomized droplet distribution over the spray plume and the deposition rate. This analysis was conducted using a three-dimensional (3D) Eulerian–Lagrangian model to describe the two-phase spraying flow by extending the base OpenFOAM package. The procedure includes an unsteady compressible Navier–Stokes solver combined with a large Eddy simulation approach to model turbulence effects on the air flowfield. This is coupled to the spray dynamics by including droplet trajectory tracking, wall film dynamics, and electric field charge. The approach is further extended to include the evaporation phenomenon and the transport of its products. Compared to a conventional ERBS, herein, we provide an in-depth analysis of the fluid dynamic characteristics around the ERBS with a control-ring field pattern for vorticity, velocity, and electrical fields. The results indicate that the control-ring operation improves the performance and transfer efficiency of the ERBS, and it also helps to harmonize the direction of the charged paint droplets. For the first time, finding a balance between the effect of the inside bell cup surface and control-ring voltage and charged droplet has been conducted.