AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
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Modeling Simultaneous Coagulation and Charging of Nanoparticles at High Temperatures Using Moment Lognormal Size Distribution
GIRISH SHARMA, Yang Wang, Rajan Chakrabarty, Pratim Biswas, Washington University in St Louis
Abstract Number: 790 Working Group: Nanoparticles and Materials Synthesis
Abstract A large amount of chemically and thermally ionized species is produced in the flames. During flame synthesis of nanoparticles, these ions collide with particles while particles coagulate among themselves. Both the phenomenon of charging and coagulation decide the particle size distribution but the existing models do not consider the coupling of these two effects. In the past, detailed two-dimensional discrete-sectional population balance modeling has been conducted but it is computationally expensive. In this work, a moment model simulating simultaneous charging and coagulation is developed with the help of asymptotics and perturbation theory. This model takes care of the different charged states as well as particle size distribution in each charged state and their interactions. This model is then compared with a monodisperse model incorporated with coagulation and charging mechanisms. Following this, the effects of particle and ion concentrations on particle growth in bipolar/unipolar environment are studied.
To achieve this, a simplified polynomial expression for charging coefficient is derived from Fuchs expression. This expression is found to be in good agreement with the complete Fuchs theory expression at high temperatures in the free molecular regime. This expression is then used in the general dynamic equation for simultaneous charging and coagulation to derive moment balance equations. Both the models, monodisperse and moment show very good agreement for different simulated cases. They show that influence of charging is more prominent when the particle concentration was comparable to or lesser than the ion concentration. This also confirms that monodisperse model is able to capture the phenomenon in most of the cases.