Particle–Focusing Characteristics of Matched Aerodynamic Lenses

Forming collimated and size–selected particle beams is a necessary component of certain instruments and industrial processes. An ideal aerosol inlet produces particle beams at high efficiency and transmission rate. The particle transmission rate can be maximized by slot geometries to generate a tightly focused particle beam that is confined to a desired volume. Traditionally, orifices and capillaries have been employed to generate focused particle beams where particle inertia is used to separate them from the carrier gas. The goal of this work is to improve the current inlet geometries for enhanced transmission of particles. For this purpose, we propose a novel inlet geometry that comprises a series of matched capped slots upstream of a choked orifice inlet. By adjusting the pressure, the geometry transmits an arbitrary particle size with high efficiency while maintaining a high flow rate. The slot dimensions can be analytically determined by constraining the design such that the slots and choked orifice focus the same particle sizes and have the same mass flow rate. Numerical simulations of the flow and particle trajectories through the inlet are carried out using the CFD code FLUENT. The new geometry is found to enhance the focusing characteristics of the orifice while maintaining the high flow throughput. The geometry is further optimized to maximize the transmission rate.

Acknowledgments

This work was supported by the EPA supersite programs via funding to the Pittsburgh and Baltimore supersites.