Numerical Simulation of the Electrostatic Coating Process: the Effect of Applied Voltage, Droplet Charge and Size on the Coating Efficiency

Electrostatic Rotary Bell Sprayers (ERBSs) have been widely used in the painting industry, especially in the automotive and aerospace industries, due to their superior performance. The effects of the applied voltage and paint droplet charge values on the spraying pattern and coating Transfer Efficiency (TE) in the ERBS, including a high-voltage ring for spray cloud control, have been studied numerically in a wide range of droplet size distribution. A 3D Eulerian-Lagrangian numerical analysis is implemented under the framework of the OpenFOAM package. The fluid dynamics of turbulence, primary and secondary breakup procedures are modeled using a large eddy simulation (LES) model, Rosin-Rammler distribution, and modified TAB approach, respectively. Compared to the conventional ERBSs, in the current work an exhaustive exhibition of the airflow dynamic and spray pattern characteristics around the ERBS with outer high-voltage control-ring field pattern, i.e., velocity, vorticity, electric potential field, overspray, film thickness are reported. Our findings indicate that the control-ring around the rotary bell rim improves the coating procedure TE and produces a more harmonized and narrower spray plume. Our in-depth investigation clearly shows the importance of the droplet charge values, voltage quantity, and considered droplet size range on the film thickness and its corresponding quality that is obtained from the workpiece.