大气气溶胶自保守混凝动力学渐进性行为的数值模拟
发布时间：2018-07-25 08:03
【摘要】：空气之于人类犹如阳光之于花朵。随着中国城镇化建设步伐的加快,以煤炭为主体的能源结构导致的燃料废气、逐年增加的机动车保有量带来的汽车尾气等许多因素把大气气溶胶污染推到了人类面前。大气中二氧化硫、氮氧化物、氨等污染物在适宜的条件下就会形成气溶胶颗粒物,引发雾霾等环境问题,影响气候、大气能见度、人体健康等多个方面。气溶胶颗粒的粒径分布决定其影响程度,混凝是颗粒成长过程中的重要物理过程。本文围绕大气气溶胶颗粒的自保守混凝动力学展开,主要可以分为两个部分:第一部分是关于混凝动力学、碰撞机制与碰撞频率函数、自保守理论等方面的基础研究和理论推导;第二部分是关于对基于离散型群体平衡方程建立的自保守混凝动力学模型进行计算机模拟实验及结果分析。论文将分形维数和粒子碰撞机制两个因素设计组合模拟实验,通过体积分域方法将理论模型划分成维度为30的一阶线性常微分方程组并借助MATLAB软件进行求解,研究气溶胶颗粒从混凝开始至到达自保守状态的粒径渐进演化全过程,得到气溶胶颗粒的自保守分布谱并分析其自保守特征。研究结果表明在单一布朗运动作用或布朗运动和流体剪切共同作用下球形和分形气溶胶颗粒粒径函数均呈现出钟罩型自保守分布,即在混凝进行一定时间后,气溶胶颗粒的粒径分布不依赖于时间而发生变化。在此过程中,分形维数和颗粒的碰撞机制都对混凝过程产生显著影响。分形维数决定气溶胶颗粒的空间结构,分形维数越小颗粒的空间结构越开放,从而产生更大的碰撞面积,混凝达到自保守状态的时间越短;碰撞机制控制气溶胶颗粒的碰撞频率函数,较高的碰撞频率使粒子迅速碰撞结合形成聚集体。另外,通过计算不同情况下布朗运动和流体剪切共同作用下的颗粒混凝情况得到了一个平衡点。当流场的剪切强度小于此平衡点时,布朗运动作用在粒子的碰撞机制中占优;反之,流体剪切作用占优。
[Abstract]:Air is to man what sunshine is to flowers. With the acceleration of China's urbanization construction, many factors, such as fuel emissions caused by coal energy structure and automobile exhaust gas caused by increasing vehicle ownership, have pushed atmospheric aerosol pollution to human face. Atmospheric pollutants such as sulfur dioxide, nitrogen oxide, ammonia and so on will form aerosol particles under suitable conditions, causing environmental problems such as haze, affecting climate, atmospheric visibility, human health and so on. The size distribution of aerosol particles determines the degree of influence, and coagulation is an important physical process in the process of particle growth. This paper focuses on the self-conserved coagulation dynamics of atmospheric aerosol particles, which can be divided into two parts: the first part is about coagulation dynamics, collision mechanism and collision frequency function. The second part is about the computer simulation experiment and the result analysis of the self-conservative coagulation dynamic model based on discrete population equilibrium equation. In this paper, the fractal dimension and particle collision mechanism are combined to design simulation experiments. The theoretical model is divided into first order linear ordinary differential equations with dimension 30 by volume domain method and solved by MATLAB software. The evolution of aerosol particles from coagulation to self-conserved state is studied. The self-conservative distribution spectrum of aerosol particles is obtained and its self-conservative characteristics are analyzed. The results show that under the action of single Brownian motion or the interaction of Brownian motion and fluid shear, both spherical and fractal aerosol particle size functions show a bell-shaped self-conserved distribution, that is, after coagulation for a certain time. The particle size distribution of aerosol does not depend on time. In this process, the fractal dimension and particle collision mechanism have a significant impact on the coagulation process. The fractal dimension determines the spatial structure of aerosol particles. The smaller the fractal dimension is, the more open the spatial structure is, and the larger the collision area is, the shorter the time for coagulation to reach self-conservative state is. The collision mechanism controls the collision frequency function of aerosol particles, and the higher collision frequency causes the particles to collide rapidly to form aggregates. In addition, a equilibrium point is obtained by calculating the particle coagulation under the interaction of Brownian motion and fluid shear. When the shear strength of the flow field is smaller than the equilibrium point, the Brownian motion dominates the collision mechanism of the particle, whereas the fluid shearing is dominant.
【学位授予单位】：北京交通大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：X513
本文编号：2143163
[Abstract]:Air is to man what sunshine is to flowers. With the acceleration of China's urbanization construction, many factors, such as fuel emissions caused by coal energy structure and automobile exhaust gas caused by increasing vehicle ownership, have pushed atmospheric aerosol pollution to human face. Atmospheric pollutants such as sulfur dioxide, nitrogen oxide, ammonia and so on will form aerosol particles under suitable conditions, causing environmental problems such as haze, affecting climate, atmospheric visibility, human health and so on. The size distribution of aerosol particles determines the degree of influence, and coagulation is an important physical process in the process of particle growth. This paper focuses on the self-conserved coagulation dynamics of atmospheric aerosol particles, which can be divided into two parts: the first part is about coagulation dynamics, collision mechanism and collision frequency function. The second part is about the computer simulation experiment and the result analysis of the self-conservative coagulation dynamic model based on discrete population equilibrium equation. In this paper, the fractal dimension and particle collision mechanism are combined to design simulation experiments. The theoretical model is divided into first order linear ordinary differential equations with dimension 30 by volume domain method and solved by MATLAB software. The evolution of aerosol particles from coagulation to self-conserved state is studied. The self-conservative distribution spectrum of aerosol particles is obtained and its self-conservative characteristics are analyzed. The results show that under the action of single Brownian motion or the interaction of Brownian motion and fluid shear, both spherical and fractal aerosol particle size functions show a bell-shaped self-conserved distribution, that is, after coagulation for a certain time. The particle size distribution of aerosol does not depend on time. In this process, the fractal dimension and particle collision mechanism have a significant impact on the coagulation process. The fractal dimension determines the spatial structure of aerosol particles. The smaller the fractal dimension is, the more open the spatial structure is, and the larger the collision area is, the shorter the time for coagulation to reach self-conservative state is. The collision mechanism controls the collision frequency function of aerosol particles, and the higher collision frequency causes the particles to collide rapidly to form aggregates. In addition, a equilibrium point is obtained by calculating the particle coagulation under the interaction of Brownian motion and fluid shear. When the shear strength of the flow field is smaller than the equilibrium point, the Brownian motion dominates the collision mechanism of the particle, whereas the fluid shearing is dominant.
【学位授予单位】：北京交通大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：X513
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