Flow Visualization Techniques for the Evaluation of Non-Contact Trace Contraband Detectors

Abstract

Efforts are underway in the Surface and Microanalysis Science Division at the National Institute of Standards and Technology to study trace aerodynamic sampling of explosive particles using walk-through portal-based detection systems. Explosive trace detection portals are designed to screen human subjects for contraband particles and vapors. A human subject walks into a confining space where they are interrogated by a series of pulsed air jets and are screened for explosive materials by a chemical analyzer. The screening process requires particle and vapor removal, transport, collection, desorption, and detection. Aerodynamic sampling is the critical front-end process for effective detection. In this paper, various visualization techniques are employed to study portal-based aerodynamic sampling in detail. Particle lift-off and removal is visualized using high-speed videography, transport of air and particles by laser light scattering, and desorption surface heating and cooling patterns by infrared thermography. These tools are used to identify sampling inefficiencies and may be employed to study air and sea cargo screening and other methods of aerodynamic sampling of particles.