A Review of Aerodynamic Lenses Development, Challenges, and Needs

XIAOLIANG WANG, Salix Bair, Harrison Griffin, Mustafa Hadj Nacer, Bjoern Bingham, W. Patrick Arnott, Judith Chow, John Watson, Desert Research Institute

     Abstract Number: 106
     Working Group: History of Aerosol Science

Abstract
Aerodynamic focusing lenses use a series of orifices (lenses) to generate a low-diverging particle beam, allowing particles to be efficiently delivered from ambient environments to a vacuum. They have been widely used as inlets for aerosol mass spectrometers. Most lenses used today are similar to the original design invented in early 1990s, with an effective focusing size range of approximately 30–600 nm. Several design extensions over the past several decades include: 1) nanoparticle lenses for focusing <30 nm particles; 2) “ambient” lenses for focusing particles up to 2.5 µm or even 10 µm to study PM_2.5, PM₁₀, or bioaerosols; 3) high flow rate lenses to increase particle throughput; and 4) ambient pressure lenses to extend to near ambient pressure applications. There are several fundamental and practical challenges in lens design and use. For example, the orifice jet flow is inherently unstable and increasing the flow rate leads to turbulence that destroys particle focusing. However, the critical Reynolds number that leads to laminar-to-turbulent transition is not well known. Novel focusing lens geometries to maintain laminar flow at higher Reynolds numbers have been proposed but have not been experimentally validated due to difficulties in manufacturing such lenses. Advances in 3D printing technology provide opportunities for building novel lenses. This presentation reviews the history of lens development, discusses common challenges, and provides insights for new lens designs.