Numerical simulation of the gas flow field of electrostatic rotary-bell spray system

Electrostatic rotary-bell sprayer is widely used for coating conductive substrates. The combination of a high-velocity focusing air, an imposed electric field and charged droplets, leads to higher transfer efficiency than that of conventional spray coating. In this paper, the numerical simulation of the gas flow field of an electrostatic rotated bell sprayer has been obtained by solving the time averaged Navier-Stokes equations in connection with suitable closure models for turbulence (RNG and realizable ^k-ε). It is found that the gas flow plays an important role on the particle trajectories near the edge of the bell-cup. It gives the particles a high axial acceleration and assists the droplets in reaching the target. Near the substrate the axial velocity of the air flow close to zero, momentum and electrostatic forces guide the larger droplets toward the grounded disc, the small droplets continue to be carried away by the air stream. The presence of turbulence causes a randomization in the droplet trajectories so that even droplets with similar characteristics do not share the same path.