The Effects of Jet Axis Switching and Aerodynamic Focusing on Deposition Patterns in Converging-Diverging Slit Impactors

YENSIL PARK, Tomoya Tamadate, Bernard Olson, Thomas Schwartzentruber, Christopher J. Hogan, University of Minnesota

     Abstract Number: 131
     Working Group: Aerosol Physics

Abstract
The widths of the deposition patterns of particles accelerated through high-aspect-ratio slit nozzles are influenced by aerodynamic focusing. However, "jet-axis switching", a phenomenon that major and minor axes of the jet flow profile interchange, can also affect the orientation and shape of particle deposits, and in some instances, lead to deposits which are nearly perpendicular in orientation to the nozzle orientation. The combined influences of jet-axis switching and aerodynamic focusing on how particles deposit in slit impactor systems has been incompletely described. In this study, we investigate the deposition behavior of monodisperse particles ranging from 100 nm to 5 µm in diameter in a converging–diverging slit nozzle system under upstream pressure of 252 Torr in air. We vary the downstream pressure (3–50 Torr) and the nozzle-to-substrate distance (90–248× throat width) to characterize how these parameters impact deposition. Depending on particle size and flow conditions, deposits either align with the nozzle geometry, rotate 90°, or become tightly focused and symmetric. Our results show that jet-axis switching is more pronounced for smaller particles, higher downstream pressures, and longer nozzle-to-substrate distances. The degree of switching and the deposit area are both inversely proportional to the particle Stokes number. The degree of switching and the deposit area are both inversely proportional to the particle Stokes number.