Measurements of the Physical Decay Rates of Aerosols in a Rotating Drum
DEEPAK SAPKOTA, Hui Ouyang, University of Texas at Dallas
Abstract Number: 326
Working Group: Aerosol Physics
Abstract
Rotating drums have been extensively used in the retention of aerosols for longer duration of time for various applications including bioaerosols transmission, inhalation toxicology, immunology, and drug delivery. Particularly, it is important to accurately quantify the physical decay rate (the deposition rate of particles to the wall) for bioaerosol studies, to improve accuracy for the biological decay of airborne pathogens. In this study, we focus on measuring the physical decay rates spanning from nanoparticles to sub-10 μm particles and subsequently compare the experimental findings with existing theoretical models. Polydisperse aerosols of KCl, generated using a 4-jet BLAM nebulizer, are introduced into a 40L Goldberg rotating drum, where they remain suspended for a duration of five hours. To prevent coagulation between nanoparticles (<1μm) and larger sub-10 μm particles, we employ a virtual impactor to introduce nanoparticles or larger particles separately into the drum during loading. The number concentration of aerosols inside the drum was measured with SMPS (Scanning Mobility Particle Sizer- TSI) for nanoparticles and APS (Aerodynamic Particle Sizer -TSI) larger sub-10 μm particles. The decay rates, represented by k (#/second), in an exponential decay model (the number concentration decays exponentially with time) are dependent on particle size. Interestingly, they follow a U-shape pattern with the particle size: for nanoparticles, the decay rate increases as particle size decreases, while for sub-10 μm particles, it increases as particle size increases. Comparative analysis of measurements with diverse theoretical models suggests that turbulent diffusion primarily governs particle loss for nanoparticles, while inertia becomes significant for sub-10 μm particles. Given the absence of accurate models covering both nano- and micro-size particle loss in the rotating drum, this study sets the stage for developing an improved model to characterize particle loss under varying operating conditions of the rotating drum.