Cooling, freezing and substrate impact of droplets formed by rotary atomization

Abstract

A simple model is developed for the cooling and freezing prior to substrate impact of droplets generated by rotary atomization. Application of the model accounts for Busk's observation in 1960 that droplets below a certain size were solid on impact with the 6 m diameter chamber walls of his apparatus. Application to smaller-scale apparatus indicates negligible cooling or freezing prior to impact. Calculations indicate that termination of flattening after impact could not have resulted from freezing. However, an alternative mechanism of conversion of kinetic to viscous energy predicts too small a terminal thickness by a factor of at least five. The implied restraint in viscous deformation might have arisen from oxide film formation on the droplet surfaces.