Aerosol focusing in micro-capillaries: Theory and experiment

A combined theoretical and experimental study is presented where we illustrate the focusing influence of Saffman force upon the fluid dynamics of aerosol flows through micro-capillaries. It is shown that under proper conditions, the Saffman force acting on aerosol particles in gas flowing through a micro-capillary causes migration of particles toward the center line of the capillary. This approach is in stark contrast to the classical aerodynamic focusing methodologies where only particle inertia and the Stokes force of gas–particle interaction are typically considered. A new mathematical model for aerosol flow through a micro-capillary accounting for complicated interactions between particles and carrier gas is presented and this model describes the experimental observables obtained via imaging microscopy of a beam of aerosol particles (d∼1μm). In general, this study affords a method for controlling and optimizing focused aerosol beams by appropriate modification of process variables such as the micro-capillary geometry, the carrier gas composition and the nature of the aerosol particles.