Aerodynamic focusing of inertial particles in supersonic micronozzles

A particle-laden flow in a supersonic micronozzle is studied using a one-way coupled two-fluid approach. The carrier gas parameters are obtained from the numerical solution of the Navier-Stokes equations, rarefaction effects are taken into account by imposing velocity slip and temperature jump boundary conditions on the nozzle walls. Under conditions considered, the flow around particles is transitional and free-molecular. As a result of numerical solution of the dispersed-phase equations in Lagrangian variables, two types of particle motion in the expanding part of the nozzle are detected: particle spraying and particle accumulation. The particle focusing effect is most pronounced for particles of about 1–2 µm in size. The particle number density fields contain singularities appearing on the envelopes of particle trajectories. However, the model of non-colliding particles remains valid because the mean distance between the particles near the singularities remains much greater than the particle size. The aerodynamic scheme of aerosol particle focusing proposed may be used in various technologies (microthrusters, needle-free drug injection, microfabrication, etc.). (© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)