AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
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Mobility and Sedimentation of Agglomerates with Polydisperse Primary Particles
Anastasia Spyrogianni, Katerina S. Karadima, Eirini Goudeli, Vlassis G. Mavrantzas, SOTIRIS E. PRATSINIS, ETH Zurich
Abstract Number: 79 Working Group: Aerosol Physics
Abstract The precipitation of agglomerates is important in water cleaning, pharmaceutical processing, nanotoxicology and nanomedicine as well as for the stability of engineered nanofluids. Here, the mobility of nanosized fractal-like SiO2 agglomerates in water is investigated and their settling rate in infinitely dilute suspensions is calculated by thoroughly validated Brownian dynamics tracking the agglomerate translational and rotational motion. Agglomerates are generated by an event-driven method (1) and have constant mass fractal dimension of 1.80 ± 0.01 but varying primary particle (PP) size distribution, mass and relative shape anisotropy. The calculated diffusion coefficient is used to obtain their mobility diameter dm, which is in excellent agreement with that from scaling laws for fractal-like agglomerates (2). The agglomerate mobility to gyration diameter ratio, dm/dg, decreases with increasing relative shape anisotropy κ2. For constant dm, the agglomerate settling rate, us, increases with increasing PP diameter and geometric standard deviation σp,g (polydispersity). A linear relationship between us and agglomerate mass to dm ratio, m/dm, is revealed leading to an analytical expression for calculation of us for agglomerates consisting of polydisperse PPs. This expression shows that the commonly-made assumption of monodisperse PPs underestimates us by a fraction depending on σp,g and the agglomerate mass mobility exponent. For constant fractal dimension, increasing the PP polydispersity decreases the average agglomerate dm but increases the average us. Simulations are in excellent agreement with precipitation rate measurements of steel (3) and SiO2 (4) agglomerates in oil and water, respectively.
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3. Kasper, G.; Niida, T.; Yang, M. Measurements of viscous drag on cylinders and chains of spheres with aspect ratios between 2 and 50. J. Aerosol Sci. 1985, 16, 535-556.
4. Spyrogianni, A.; Sotiriou, G.A.; Brambilla, D.; Leroux, J.-C.; Pratsinis, S.E. The effect of settling on cytotoxicity evaluation of SiO2 nanoparticles. J. Aerosol Sci. 2017, 108, 56-66.