Atomization and spray characteristics around an ERBS using various operational models and conditions: numerical investigation

Abstract

The impetus of the current paper is to conduct numerical evaluations about the fundamental behaviors of the flow in an electrostatic rotary bell sprayer (ERBS) during the formation of the droplets and depositing on a target. The effect of operational parameters like bell rotational speed, shaping air and paint flow rate, electrical charge values and droplet distributions are considered precisely. Here, an Eulerian-Lagrangian algorithm that contains a model for airflow field, spray dynamics, electric charge field, droplet trajectory tracking and wall film dynamics has been extended by using the OpenFOAM package. The fluid dynamics is computed by using a large eddy simulation (LES) turbulence model. The mechanism of atomization is facilitated by the action of the centrifugal force that conducted the disintegrated droplets to the cup edge. Following that, the high-velocity droplets affected by the shaping airflow and electric force are transported towards the workpiece. The effect of the bell rotational speed in comparison with other parameters is dominant. The measured size of the droplets is controlled by increasing the bell rotational speed or decreasing the paint flow rate, in this case, promoting a reduction in droplet size. The droplet size near the bell cup was increased noticeably, however, their radius becomes more uniform at a longer lateral distance. Investigation of the various breakup models is one of the main goals of this work to predict the droplet size more precisely. The Reitz-KHRT, Reitz-Diwakar, Pilch-Erdman and the newly modified TAB model are examined in order to predict the breakup process in the ERBS. As the paint droplets are a viscous fluid a modification of the Taylor Analogy Breakup (TAB) approach taking non-linear influences for large viscosity into account is recommended. The use of the breakup models creates a smaller droplet size and this means they are more sensitive to recirculation regions flow pattern. The implemented wall film function was able to predict the transport in the boundary layer over the target. The numerical results describe exact values for the size, distribution, velocity and trajectory of the particles in ERBS, and these results are important for coating industries, in order to optimize their working conditions.