Date of Award
Doctor of Philosophy (PhD)
Dr. John R. Saylor
Dr. Joshua Bostwick
Dr. Phanindra Tallapragada
Dr. Xiangchun Xuan
The application of particle size measurement extends across many fields: air quality measurement, pharmaceutical studies, paint and coating production, and nanoparticle formulation to name a few. Therefore, accurate measurement of nanoparticles is critical to aerosol science. While devices currently exist that can size and count nanoparticles such as electrical mobility spectrometers, dynamic light scattering devices, and small angle X-ray scattering devices, their high costs, complex operation, and lack of outdoor usability, restrict their use in practical applications. Among the devices that can size aerosols down to the nanoscale, cascade impactors stand out because of their robustness, relatively simple design, low cost, and outdoor usability. Yet, particle measurement in cascade impactors is currently limited by low particle size resolution due to its design limitations. This thesis focuses on improving the particle sizing resolution in cascade impactors, especially in the nanoscale, using particle deposition patterns whose radial dimensions are sensitive to the size of their constituent particles. Formation of the size-dependent ring-shaped particle deposits has been shown to occur in previous studies and forms the motivation to perform this study. The knowledge generated from this study has the potential to enable the development of commercial inertial impactors with high resolution.
In the first part of this thesis, the effect of particle surface attraction quantified by the Hamaker constant A, and the particle elasticity quantified by the coefficient of restitution e, on particle deposition patterns in inertial impactors are studied. Firstly, experiments were conducted wherein monodisperse hygroscopic particles were passed through a nozzle and impacted on a hydrophobic surface at different flow relative humidity. The flow relative humidity affects both A and e which in turn affects the degree to which particle bounce occurs on impaction. The experimental results provided varying particle deposition patterns for a range of (A,e) by varying the flow relative humidity. These particle deposition patterns were then replicated by particle trajectory simulations wherein the flow data, the impactor design parameters, and the particle and surface properties were the input. The simulation revealed that for hygroscopic particles impacting a hydrophobic surface, the particle-surface adhesion decreases with relative humidity while the particle elasticity increases with relative humidity. The simulations also elucidated the mechanism of particle deposition in inertial impactors for such conditions.
In the second part of the thesis factors affecting the diameter of ring-shaped particle deposits D in inertial impactors were identified, and the extent to which these factors affect D was determined. The results of the experimental investigation revealed that the factors that affect D are the particle diameter d, the ratio of the nozzle-to-plate distance to the nozzle diameter S/W, the Hamaker constant A, and the coefficient of restitution e. Experiments were performed for particle sizes ranging from 50 nm to 9.2 μm, at S/W ranging from 0.03 to 0.09, and for two types of particle-surface combinations. The ring-shaped particle deposition patterns were replicated by particle trajectory simulations and the mechanism by which these deposition patterns form at different locations in the parameter space was determined. Finally, an empirical relation for the ring diameter D as a function of d, S/W, A, and e was obtained.
Kala, Shivuday, "Improving Sizing Resolution of Particle Impactors in the Nanoparticle Range" (2023). All Dissertations. 3509.