This work reports on the numerical simulation of fine powder coating process in comparison with coarse powder coating,using a commercial computational fluid dynamic code,Fluent v6.1.The purpose of the study is to understand the gas and particle flow fields inside the coating booth for various operating conditions and the effect of reducing particle size on the coating process.The air and powder particle flows in a coating booth were modeled as a three- dimensional turbulent continuous gas flow with solid powder particles as a discrete phase.The continuous gas flow was calculated by solving Navier-Stokes equations including the standard k-εturbulence model and the discrete phase based on Langrangian approach.The effect of the solid phase volumetric fraction,which is less than 0.1%,on the continuous phase was ignored and the effect of particle-particle interaction on particle trajectories was not taken into account.In addition to drag force and gravity,the electrostatic force was considered in the equation of motion and implemented using user defined function. The governing equations were solved using second order upwind scheme.The validity of the model was verified by comparing numerical velocities and diameter profiles with available experimental data. The parametric study demonstrates that the use of finer particles of size 15μm or lower can give very smooth and uniform surface finish,which may serve the requirement of automotive top clear coat.The study provides useful information about optimum operating conditions such as the airflow rate,the applied external voltage and the distance between the gun and the coating object.The numerical model can also be used to optimize the gun-booth design for a better operating efficiency.
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