Enhancing electrostatic spray-painting efficiency with modified high-voltage conductors: A numerical study on pulsed electric fields

This study presents a numerical simulation of electrostatic spraying using a rotary bell sprayer equipped with a high-voltage control ring conductor. The effects of the electric field generated by constant and pulsed voltages at various frequencies applied to the electrostatic rotary bell sprayer (ERBS) with the control ring are explored. Using the OpenFOAM computational fluid dynamics framework, the simulations employ a three-dimensional Eulerian-Lagrangian method. The implemented algorithm models fully turbulent airflow using a Large Eddy Simulation (LES) approach, along with detailed modeling of spray dynamics, electric fields, and droplet tracking. The primary objective is to investigate the influence of different voltage application modes on the spraying process, with a focus on optimizing droplet consistency and control. The impacts of constant and pulsed voltages on spray plume formation, droplet volumes, and critical spraying stages are examined. Through in-depth analysis of electric field distributions, interface charge densities, and velocity fields, the complex interactions governing pulsed and constant voltage spraying processes are elucidated. The results show that pulsed voltage applied to the control ring shapes the spray plume and alters droplet behavior, though with limited effectiveness. In contrast, applying a pulsed voltage of -40 kVrms to the sprayer's body cup at frequencies of 800 Hz and 1600 Hz significantly improves spray characteristics, resulting in a modified torus shape and a narrower size range of larger droplets compared to constant voltage condition of -40 kV. This leads to a more uniform droplet size distribution, consistent paint film, and minimal overspray. Consequently, transfer efficiency (TE) increases by 6% at 800 Hz and 4.8% at 1600 Hz compared to constant voltage. This indicates that 800 Hz is the optimal frequency for applying pulsed fields, due to its notable effectiveness in improving deposition efficiency and minimizing material waste.