Non-contact Surface Sampling: Aerodynamic Resuspension of Particulates by Planar Impinging Jet

Byron Ockerman, Kalyan Kottapalli, Guanyu Song, Patrick Fillingham, IGOR NOVOSSELOV, University of Washington

     Abstract Number: 557
     Working Group: Aerosol Physics

Abstract
Residues of hazardous substances, such as chemical compounds with low vapor pressure, radioactive particles, and biological contamination, can remain on surfaces for a prolonged time. The fate of these particles partially depends on the aerodynamic resuspension rates from the surfaces. These rates are a function of particle and surface properties and environmental conditions. Aerodynamic resuspension can be used for non-contact surface sampling. The effectiveness and sampling throughput of trace residues detection can be significantly enhanced by integrating an analytical instrument with a properly-designed sampling system. We present the analysis of the removal rates of Trimethylenetrinitramine (RDX) using an impinging flat jet as a function of the wall shear stress [1, 2]. The effect of the jet duration is studied experimentally; the removal efficiency increases slightly for greater exposure times, with most particles removed in the first 10 ms of exposure [3]. The optical analysis is compared with the chemical extraction method and analyzed by the LC-MS. The microscopic approach had errors in the 3-46% range compared with LC-MS analysis. Aerodynamic removal efficiency from Nylon was quantified using LC-MS, and the same flow conditions yielded greater removal efficiency from fibrous substrates compared to smooth substrates. The LC-MS method for RDX removal analysis has shown good repeatability and was effectively used for trace particle resuspension analysis from fibrous substrates, where the optical method had significant limitations.

The non-contact surface sampler was developed utilizing opposing planar jets geometry that enables aerodynamic trapping of particles. Angled jets direct a large fraction of the flow toward the center of the sampling area, resulting in an upward flow toward the sampler inlet. The aerodynamic trapping was observed experimentally via high-speed videography coupled with Schlieren imaging and numerically by computational fluid dynamics (CFD) [4]. The flow is aspirated through the reusable collection media to ensure the most efficient capture of particles.

[1] Kottapalli, K. and I.V. Novosselov, Experimental study of aerodynamic resuspension of RDX residue. Aerosol Science and Technology, 2019. 53(5): p. 549-561.
[2] Fillingham, P., et al., Characterization of adhesion force in aerodynamic particle resuspension. Journal of Aerosol Science, 2019. 128: p. 89-98.
[3] Kottapalli, K., et al., Resuspension of trace explosive particle residues by planar impinging jet: Effects of exposure duration and wall shear stress. Journal of Aerosol Science, 2023. 167: p. 106095.
[4] Fillingham, P., et al., Drag, lift, and torque on a prolate spheroid resting on a smooth surface in a linear shear flow. Powder Technology, 2021. 377: p. 958-965.