大氣氣溶膠自保守混凝動力學(xué)漸進性行為的數(shù)值模擬
發(fā)布時間：2018-07-25 08:03
【摘要】：空氣之于人類猶如陽光之于花朵。隨著中國城鎮(zhèn)化建設(shè)步伐的加快,以煤炭為主體的能源結(jié)構(gòu)導(dǎo)致的燃料廢氣、逐年增加的機動車保有量帶來的汽車尾氣等許多因素把大氣氣溶膠污染推到了人類面前。大氣中二氧化硫、氮氧化物、氨等污染物在適宜的條件下就會形成氣溶膠顆粒物,引發(fā)霧霾等環(huán)境問題,影響氣候、大氣能見度、人體健康等多個方面。氣溶膠顆粒的粒徑分布決定其影響程度,混凝是顆粒成長過程中的重要物理過程。本文圍繞大氣氣溶膠顆粒的自保守混凝動力學(xué)展開,主要可以分為兩個部分:第一部分是關(guān)于混凝動力學(xué)、碰撞機制與碰撞頻率函數(shù)、自保守理論等方面的基礎(chǔ)研究和理論推導(dǎo);第二部分是關(guān)于對基于離散型群體平衡方程建立的自保守混凝動力學(xué)模型進行計算機模擬實驗及結(jié)果分析。論文將分形維數(shù)和粒子碰撞機制兩個因素設(shè)計組合模擬實驗,通過體積分域方法將理論模型劃分成維度為30的一階線性常微分方程組并借助MATLAB軟件進行求解,研究氣溶膠顆粒從混凝開始至到達自保守狀態(tài)的粒徑漸進演化全過程,得到氣溶膠顆粒的自保守分布譜并分析其自保守特征。研究結(jié)果表明在單一布朗運動作用或布朗運動和流體剪切共同作用下球形和分形氣溶膠顆粒粒徑函數(shù)均呈現(xiàn)出鐘罩型自保守分布,即在混凝進行一定時間后,氣溶膠顆粒的粒徑分布不依賴于時間而發(fā)生變化。在此過程中,分形維數(shù)和顆粒的碰撞機制都對混凝過程產(chǎn)生顯著影響。分形維數(shù)決定氣溶膠顆粒的空間結(jié)構(gòu),分形維數(shù)越小顆粒的空間結(jié)構(gòu)越開放,從而產(chǎn)生更大的碰撞面積,混凝達到自保守狀態(tài)的時間越短;碰撞機制控制氣溶膠顆粒的碰撞頻率函數(shù),較高的碰撞頻率使粒子迅速碰撞結(jié)合形成聚集體。另外,通過計算不同情況下布朗運動和流體剪切共同作用下的顆�；炷闆r得到了一個平衡點。當流場的剪切強度小于此平衡點時,布朗運動作用在粒子的碰撞機制中占優(yōu);反之,流體剪切作用占優(yōu)。
[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.
【學(xué)位授予單位】：北京交通大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：X513
本文編號：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.
【學(xué)位授予單位】：北京交通大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：X513
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相關(guān)期刊論文 前3條
1 LIN JianZhong;CHEN ZhongLi;;A modified TEMOM model for Brownian coagulation of nanoparticles based on the asymptotic solution of the sectional method[J];Science China(Technological Sciences);2013年12期
2 吳幼明;何小媚;;一類常系數(shù)微分方程組的通解[J];四川理工學(xué)院學(xué)報(自然科學(xué)版);2006年02期
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