AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
Resuspension Rates of Energetic Materials in an Aerodynamic Flow Cell
KALYAN KOTTAPALLI, Igor Novosselov, University of Washington
Abstract Number: 105 Working Group: Aerosol Physics
Abstract Most modern explosives have very low vapor pressures at room temperature. Because of that low volatility, small particles of explosive materials that are inadvertently deposited on surfaces remain accessible for long times, but, although high sensitivities have been achieved with many of these instruments, direct detection by gas sampling alone continues to be a challenging task. The effectiveness of trace explosives detection can be greatly enhanced by combining the analytical instrument with a sampling system that delivers the particles from the suspect surface directly to the analyzer. Aerodynamic non-contact sampling provides a fascinating, yet a challenging solution to this problem. Currently, comprehensive understanding of aerodynamic particle removal from surfaces has yet to be accomplished due to the difficulty in characterizing dependence on factors such as particle size, morphology, material, humidity, and turbulence. We studied the removal rates of two different types of trace explosives in an aerodynamic flow cell under various flow conditions. Samples of Trimethylenetrinitramine (RDX) and 2,4,6- Trinitrotoluene (TNT) were dry transferred to the glass surface and interrogated within an aerodynamic flow cell. The particles are examined optically and binned using an automated scanning software. The resuspension efficiency is calculated optically as a function of particle size and morphology. This model is applied to surrogates particles, and the particle size range is chosen based on the typical size distribution associated with trace explosives found in fingerprints. surface. We combine the use of particle removal data from a controlled flow cell experiment with Computational Fluid Dynamics (CFD) modelling to study the effect of wall shear stress on particle resuspension in the constant wall shear stress environment of the flow cell. Removal efficiency is proportional to the height (critical dimension) and inversely proportional to the dimension in the plane of the substrate. Wall shear stress shows a direct correlation with the aerodynamic particle removal rates.