Experimental and theoretical investigation of rotary atomization dynamics for control of microparticle size during spray congealing process
Cody A. Prather, Christopher D. Craig, John M. Baumann, Michael M. Morgen
Abstract
Experiments were conducted to characterize a rotary spray atomization and congealing process using model formulations that encompass both inviscid fluids and high-loaded suspensions. This study determined the atomization dynamics and its influence on the critical quality attribute of particle size to design a robust process with accurate particle size control. The experimental atomization regimes were identified and cross referenced with existing literature, the ideal operating range was identified, predictive particle size models were developed, and a framework for designing a robust melt-spray-congeal process across a range of formulations was outlined. Specifically, it was found that suspensions behave differently from inviscid fluids, and demonstrate more robust atomization. Inviscid fluids exhibit three distinct atomization regimes (direct drop regime (DDR)1, ligament regime (LR)2, and sheet regime), and are generally in agreement with those predicted by Frost [1]. Particle size is regime dependent, where DDR can be predicted by a modified Liu equation and LR a modified Kitamura equation. Lastly, inviscid fluids are sensitive to standing and radially propagating wave film instabilities that create larger particles and widen the particle size distribution. In contrast, suspensions don’t exhibit the three distinct regimes as predicted by Frost [1]. Rather, the suspended particles aid in the breakup by creating perforations that dominate atomization and thus, effectively suppress the sheet regime and expand the ideal operating space. Therefore, particle size can be predicted by a single Kitamura equation. Finally, they mitigate film instabilities making the process inherently robust.