ATOMIZATION OF MOLTEN MATERIALS FOR PARTICLE COATING: PREDICTION OF MEAN DROPLET SIZE FOR TWO-FLUID NOZZLES

摘要

Coating is the process of covering solid particles' surfaces with a homogeneous layer of a coating agent comprising one or multiple components. For processes carried out in fluidized beds, coating is achieved by spraying the coating agent on the particles in suspension. The aim of the present work was to study the atomization of molten materials prior to their application to powder coating in fluidized beds. Several external mixing binary nozzles were used for the atomization of a stearic-palmitic acid mixture and different polyethylene glycol grades (1000, 1500, 2050, 4000, and 6000) at different temperatures (60 degrees C, 70 degrees C, 80 degrees C, and 90 degrees C). The droplet size distributions, from which experimental mean droplet sizes were calculated, were measured by the laser diffraction technique. Subsequently, mean droplet sizes were satisfactorily modeled using different correlations reported in the literature. For a given nozzle, it was found that some fitting parameters were constant for all the polyethylene glycol grades, whereas others showed a dependency with the material viscosity. This latter was the property with the highest variability over the experimental domain. The fitted models did not provide a good prediction of the experimental data corresponding to different nozzle configurations or molten materials; therefore, new fittings were performed. This fact highlights the difficulty in obtaining models at least applicable to the atomization of molten materials.