Primary breakup of a non-Newtonian liquid using a high-speed rotary bell atomizer for spray-painting processes

Abstract

The present contribution deals with numerical and experimental studies of the primary liquid breakup process using a high-speed rotary bell atomizer. The first part of the investigations focuses on the film formation on the distributor disk and the inner surface of the rotary bell. Numerical simulations using the volume-of-fluid approach were carried out. A non-Newtonian liquid that has shear-thinning behavior is used to investigate the effect of the viscosity on the initial wetting, the film formation process, and the film thickness distribution on the bell. A nonhomogeneous film structure is found on the inner surface of the rotary bell. This is also observed in experimental investigations using a high-speed camera. The second part focuses on the disintegration process of the paint liquid in the near bell region. As inlet conditions for the breakup simulations, the properties of the liquid film at the bell edge, i.e., film thickness, velocities, and apparent viscosity, resulting from the film formation simulations were applied. Two different liquid disintegrations in the near-field were found, which were also observed in experimental investigations using a high-speed camera. Furthermore, user-defined functions were compiled in ANSYS Fluent to uniquely identify and characterize droplets formed through the breakup process. In this way, droplet properties such as diameter, velocity, and position can be determined.