Author: Liu, Hongmei
Title: Monte Carlo simulation of aerosol dynamics in turbulent flows
Degree: Ph.D.
Year: 2018
Subject: Hong Kong Polytechnic University -- Dissertations
Dynamics of a particle
Department: Dept. of Mechanical Engineering
Pages: xxv, 198 pages : color illustrations
Language: English
Abstract: The study of aerosol dynamics is of great importance to a variety of scientific and engineering fields including atmospheric science, air pollution control, industrial production, and combustion and chemical engineering sciences. A new differentially weighted operator splitting Monte Carlo (DWOSMC) method is first proposed and developed in the present study in which weighted simulated particles and operator splitting technique are coupled to improve the computational accuracy and efficiency of traditional Monte Carlo methods in simulating complex aerosol dynamics. This newly proposed and developed DWOSMC method is first verified in one-component aerosol systems by comparing its numerical simulation results with the corresponding analytical solutions for several typical cases and the sectional method for some complex cases in excellent agreement. The numerical simulation results demonstrate that this DWOSMC method has high computational efficiency and accuracy in solving complex aerosol dynamic problems where nucleation, coagulation and condensation processes simultaneously take place. This DWOSMC method is further extended to simulate multi-component aerosol systems. The results obtained from DWOSMC method are compared with a sectional method for various regimes of simultaneous coagulation and condensation processes in two-component aerosol systems. It is proved that this DWOSMC method is more computationally efficient than the sectional method in simulating two-component aerosol systems. Furthermore, the DWOSMC method is able to predict the particle number density, total particle volume, particle number distribution and component-related particle volume density distributions as well as the bivariate compositional distribution.
In order to solve multi-dimensional aerosol dynamics interacting with fluid phase, the Monte Carlo method for describing particle dynamics is coupled with computational fluid dynamics (CFD) under the Eulerian-Lagrangian reference frame. The formulated CFD-Monte Carlo method is firstly used to simulate a spatially inhomogeneous particle-laden turbulent flow. The effects of two-way coupling, turbulent dispersion model and Reynolds number based on a square rod obstacle on the particle dispersion pattern are fully studied for a wide range of particle Stokes number. Finally, the formulated CFD-Monte Carlo method is used to study aerosol dynamics in turbulent flows. The DWOSMC method is coupled with large eddy simulation (LES) to examine the evolution and growth of aerosol particles in a turbulent planar jet. Firstly, the newly developed LES-DWOSMC method is verified by the results obtained from a direct numerical simulation-sectional method (DNS-SM) for coagulation occurring in a turbulent planar jet from available literature. The fluid velocity field and the time-averaged particle diameter distribution obtained from LES-DWOSMC show good agreement with those obtained from DNS-SM. The coherent vortex structures of fluid gas have a significant impact on the aerosol particle dispersion patterns. Then the effects of jet temperature and jet Reynolds number on the evolution of time-averaged mean particle diameter, normalized particle number concentration and particle size distribution (PSD) are fully investigated. The jet temperature and jet Reynolds number prove to be two important parameters that can be used to control the evolution and pattern of PSD in aerosol reactors. This developed LES-DWOSMC method proves to be able to predict and render a better understanding of the evolution and growth of the particle size distribution (PSD) of the aerosols in turbulent flow. In summary, this newly proposed and developed CFD-DWOSMC method in the present study has demonstrated high capability in the numerical simulation of complex aerosol dynamics in turbulent flows.

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