树枝尺度的植物在风洞内对气溶胶颗粒物的捕集效率

发布时间：2018-05-18 03:12

本文选题：气溶胶颗粒物 + 风洞　；参考：《东华大学》2017年硕士论文

【摘要】：由于颗粒物影响全球气候系统,目前人们对颗粒物的兴趣正呈指数递增,对于颗粒物捕集的研究已经成为气象科学和空气污染研究的一个主要课题。此外,颗粒物对健康具有不利影响,例如呼吸道疾病和心血管疾病的加重与颗粒物密切相关。颗粒物的一个重要特点是它会附着于植物,并可通过植物除去。因此,全世界种植树木以用来防风固沙。在中国的北方城市,常绿植物的叶片可以对粉尘进行有效地吸附。树枝尺度叶片的空间分布比生态系统中树冠内的叶片分布简单的多,同时这样的规模仍然提供了足够多数量的叶子用于吸附气溶胶颗粒物,因此,了解叶片和生态系统之间的中间尺度的颗粒物沉积是必要的,而风洞试验是一种研究气溶胶颗粒物在树枝尺度植物上沉积的有效方法。虽然这种风洞设置没有解决生态系统中气溶胶颗粒物沉积的所有复杂性,但是它确实对所有气溶胶颗粒物通过布朗扩散沉积的这一共同的关键过程进行了放大,为当前的可吸入颗粒物的治理提供参考。因此,本文通过风洞试验研究植物的流动阻力及颗粒物在植物上的沉积速度。为了获得植物的流动阻力及颗粒物的沉积速度,本课题以三种植物(小叶黄杨、橡树以及松树)为研究对象,通过试验测量,表明了其叶面积指数与填充密度之间的关系,并通过试验测试分别提出植物的流动阻力以及颗粒物沉积速度的关系表达式。主要研究工作和研究结论如下:(1)为了获得树枝尺度植物的捕集效率及流动阻力,通过搭建风洞试验台,在不同工况下分别测定树枝尺度的植物对气溶胶颗粒物的捕集效率,并拟合出捕集效率与气流速度、填充密度以及颗粒物粒径之间的关联式。并分别用相同工况下其他组的试验数据对关联式进行了验证,最后提出三种植物捕集效率的综合关联式。试验结果表明,树枝尺度的植物对不同粒径的气溶胶颗粒物的捕集效率随着风速的增大先减小而后增大;在不同风速下植物对不同粒径气溶胶颗粒物的捕集效率都是随着填充密度的增大而增大;不同风速下树枝尺度的植物对气溶胶颗粒物的捕集效率都是随着颗粒物粒径的增大先减小,之后随着粒径的进一步增大而增大。试验表明,气溶胶颗粒物在三种树枝尺度植物中的最大穿透粒径均为1μm,当颗粒物粒径小于1μm时,植物对颗粒物的主要捕集机理为扩散,当颗粒物粒径大于1μm时,主要的捕集机理为拦截和碰撞。同时也给出了树枝尺度植物的阻力系数与叶面积指数之间的关系式,并用试验数据对关系式进行了验证,最后给出三种植物阻力系数综合关系式。(2)为了获得颗粒物在树枝尺度植物上的沉积速度,将给定的叶面积指数的整体枝叶这些不同风速下的捕集效率值转化成沉积速度,然后计算出沉积速度的试验值。并提出了气溶胶颗粒物在三种树枝尺度植物上的沉积速度与颗粒物粒径、风速以及叶面积指数之间的相关关系。此外,依据均质纤维捕集层捕集理论计算出颗粒物在叶面上沉积速度的理论值。通过对比发现,试验测试结果与理论计算结果比较吻合,沉积速度Vd的试验值与理论计算值随颗粒物粒径的变化趋势相同,都是随着气溶胶颗粒物粒径的增大而先减少后增加。(3)为了获得灌木对颗粒物的捕集效率,通过建立典型的灌木模型,在不同工况下进行风洞试验,分别测算出灌木模型对气溶胶颗粒物的捕集效率。提出了捕集效率及其影响参数之间的关联式,并且采用非样本数据对其进行了验证。同时,采用CFD中的DPM模型进行数值模拟,模拟结果表明,捕集效率的模拟值与试验值存在一定误差,产生误差的原因为捕集体的几何网格尺寸与颗粒物粒径尺寸差距过大,如何减少模拟值与试验值的误差有待于进一步深入研究。
[Abstract]:As particulate matter affects the global climate system, the interest in particulate matter is increasing exponentially, and the study of particulate matter capture has become a major issue in the study of meteorological and air pollution. In addition, particles have adverse effects on health, such as respiratory disease and cardiovascular disease and particulate matter. One of the important features of particles is that it is attached to plants and can be removed by plants. Therefore, trees are planted all over the world to prevent wind and sand. In the northern cities of China, the leaves of evergreen plants can be effectively adsorbed on dust. The spatial distribution of tree branches is simpler than that in the canopy of the ecosystem. The size of a large number of leaves still provides enough leaves to adsorb aerosol particles. Therefore, it is necessary to understand the deposition of particles in the middle scale between the leaves and the ecosystems, and the wind tunnel test is an effective method to study the deposition of aerosol particles on a branch scale plant. It does not solve all the complexity of the aerosol particles deposition in the ecosystem, but it does magnify the common key process of all aerosol particles through Brown diffusion deposition to provide reference for the treatment of current inhalable particles. Therefore, this paper studies the flow resistance of plants through a wind tunnel test. In order to obtain the flow resistance of plants and the deposition rate of the particles, three kinds of plants (Euonymus japonicus, oak and pine) were used as the research object. The relationship between the leaf area index and the filling density was shown by experimental measurement, and the flow of plants was put forward by test and test. The main research work and research conclusions are as follows: (1) in order to obtain the capture efficiency and flow resistance of tree scale plants, by building a wind tunnel test platform, the capture efficiency of the plant to gas soluble particles in the branch scale is measured in different working conditions, and the capture efficiency is fitted. The correlation between the velocity of air flow, the density of the filling and the particle size of the particles. The correlations were verified with the experimental data of the other groups in the same working conditions. Finally, the comprehensive correlation of the three kinds of plant capture efficiency was put forward. The results showed that the collection efficiency of the plant on the aerosol particles with different particle sizes was with the wind. The capture efficiency of the aerosol particles with different particle sizes increased with the increase of the filling density at different wind speeds, and the capture efficiency of the aerosol particles in different wind speeds decreased first with the increase of particle size, followed by the further particle size. The maximum penetration of aerosol particles in three species of tree scale plants is 1 m. When the particle size is less than 1 mu m, the main trap mechanism of the plants is diffusion. When the particle size is more than 1 mu m, the main trap mechanism is intercepting and collision. The relationship between the resistance coefficient and the leaf area index is verified by the test data. Finally, the formula of three plant resistance coefficients is given. (2) in order to obtain the deposition rate of the particles on the tree scale plant, the total branches and leaves of the given leaf area index are converted to the capture efficiency values under different wind speeds. The velocity of deposition was calculated and the experimental value of deposition rate was calculated. The correlation between the deposition rate of aerosol particles on three kinds of branch scale plants and particle size, wind speed and leaf area index was proposed. The theory of deposition rate of particles on the surface of the particles was calculated according to the trap theory of homogeneous fiber trapping. By contrast, it is found that the experimental results are in agreement with the theoretical calculation. The experimental values and theoretical values of the deposition rate Vd are the same as the particle size of particles, and they all decrease first and then increase with the increase of particle size of aerosol particles. (3) in order to obtain the collection efficiency of the particles for the particles, a typical irrigation system is established. The wood model, under the wind tunnel test under different working conditions, calculated the capture efficiency of the shrub model to aerosol particles, put forward the correlation between the capture efficiency and the influence parameters, and verified it with the non sample data. At the same time, the numerical simulation was carried out by the DPM model in CFD. The simulation results showed that the capture efficiency was effective. There is a certain error between the simulated value and the test value. The cause of the error is that the gap between the geometric mesh size of the collectives and the particle size is too large. How to reduce the error between the simulated value and the test value needs to be further studied.
【学位授予单位】：东华大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：X513;X173

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