Continuously Converging Multistage Focusing Lenses to Concentrate Aerosols at High Reynolds Numbers

Abstract

All known multi-stage aerodynamic lenses able to focus sharply a wide range of particle sizes include decelerating regions where the flow becomes turbulent at Reynolds numbers Re typically of 100 or less. Here, we propose a design for a focusing concentrator operating laminarly at Re of many thousands. The particles are accelerated by the gas through a continuously converging ladder of smooth contractions, each designed such that: (1) the flow remains laminar at substantial Re; (2) a certain band of particle sizes is focused in each contraction, without substantial defocusing of larger particle focused in 1 or several preceding contractions; (3) the form, length, and ratio of entry to exit diameter of each contraction, as well as the number of consecutive contractions are chosen such that all particles within a given relatively wide range of sizes are focused at the end of the ladder of contractions into a relatively narrow focal region. The focusing virtual impactor formed by coupling this device to a pe...