A transfer efficiency model for powder coating process

The trajectories of charged powder particles in a powder coating system are governed by the electrostatic, gravitational and aerodynamic forces acting on the particles. A mathematical model of particle trajectories inside a powder coating booth must consider: (1) the aerodynamic flow field; (2) particle size and charge distributions; (3) the electrostatic field distribution; and (4) the geometry of the target. The authors' approach is to employ a grid generation and flow solver to examine the air flow pattern and an iterative technique where the charge simulation method is used to compute the electric field strength and the method of characteristics is used to compute the charge density in the gun-to-target region. The electrostatic forces due to the deposited powder layer and image charge are taken into account. The model is applied to the geometry of a high-voltage electrode consisting of a long thin rod with a hemispherical end cap and a grounded flat disk substrate. The simulation results can provide valuable information concerning particle deposition and transfer efficiency.