Study On Particle Evolution Based On The Process Of Binary Coagulation

In recent years, environmental pollution is becoming increasingly serious with the accelerated process of urbanization in China, and motor vehicle exhaust particles become one of the main pollutants in atmosphere. Studies have shown that the particle size distribution and concentration are related to the damage degree of particles to human health. The evolution of particle size distribution depends on various mechanisms, including binary coagulation process as the main mechanism. In the dissertation, the theoretical analysis and numerical simulation are adopted to study the evolution of particle size distribution. The research can deepen the understanding of the mechanism of particle evolution, further improve the theory of particle evolution,and provide the theory basis of diesel particulate emission control and indoor particulate matter control.Using the homotopy perturbation method (HPM), the binary coagulation item in the general dynamic equation of particle evolution is solved. Existence and convergence domain of the analytical solution obtained by HPM are discussed. The convergence of the homotopic perturbation approximation solution under the condition of constant coagulation kernel and initial exponential size distribution is analyzed.Through the research, the convergence condition of homotopy perturbation solution for the continuous dimensionless binary coagulation equation, the influence of particle size distribution and time interval on convergence of the approximation solution under the condition of constant kernel and initial exponential size distribution, applicable condition of HPM for the binary coagulation equation are clarified.Based on the classical thermophoresis deposition formula, the model for diesel soot particles in the cooling pipe with full development turbulent flow is established to analyze the correlation between diesel exhaust components, the particle properties and thermophoretic properties of the particles. The thermophoretic sedimentation efficiency is calculated under varying pipe scales, properties of particulate matter and exhaust flow. The results have revealed the deposition regularity of soot particles in the cooling pipe with full development turbulent flow and the key factors of diesel particulate matter emission control.The semi-implicit sectional method is used to solve the general dynamic equation describing the simultaneous coagulation and nucleation processes of vehicle exhaust particles. On the basis of the semi-implicit solution, the binary coagulation processes of diesel particulate particles of four different locations are analyzed. Time evolution of particle size distribution is studied under the process of simultaneous binary coagulation and nucleation. The results have revealed the rules of time-varying of particle size distribution in the process of binary coagulation, in the process of simultaneous coagulation and nucleation under current simulation conditions. The results also have show the influence regularity of the nucleation on the binary coagulation process.The method of moment is used to solve the general dynamics equation for in fixed space. Two key parameters are determined according to the relevant experimental results. Based on the MOM results, the correlation of particle sizes distribution evolution with coagulation, diffusion and sedimentation processes are studied. The results have revealed a characterization of the evolution of the particle size distribution in fixed space and how the particle initial concentration and size distribution, space scales effects on particle evolution of simultaneous particle coagulation, diffusion and deposition.