Research On Plant Resistance Characteristics And Capability Of Particle Collection

With the development of economy and the acceleration of industrialization and urbanization,the content of industrial plants,automobiles and buildings continues to increase,leading to a significant increase in pollutant emissions and increasingly aggravated atmospheric particulate pollution,which has a huge impact on human production and life,becoming a major issue facing China.In order to solve the problem of environmental pollution,in addition to reducing the emission of pollutants from the source,the atmospheric particulate matter that has been generated is removed through environmental engineering technical measures.As a common configuration facility in cities,green plants can effectively absorb particulate matter and remove particulate matter from the atmosphere by virtue of the complex surface of their leaves.They have become the first choice for economical and effective treatment of air pollution and are known as nature’s air filters.However,dense trees will increase air flow resistance,cause the dilution ability of pollutants weaking and the diffusion speed slowing,which is not conducive to the removal of pollutants.Therefore,it is important to study the combined effects of the characteristics of plant flow resistance and the characteristics of trapped particles.Through the appreciation and analysis of the existing relevant literature,it is found that most domestic and foreign research on the characteristics of plant flow resistance stays on the canopy scale,and there is almost no research on the microscopic leaf scale;for the "dust retention" effect of trees,domestic scholars mainly use the field The measurement method quantitatively analyzes the effect of leaf trapping particles.Foreign scholars have conducted theoretical and wind tunnel experimental studies on the dry deposition of atmospheric particles in the plant canopy,but few scholars have analyzed the mechanism of dust retention and influencing factors from the leaf level.This paper mainly uses theoretical analysis,CFD simulation and literature experimental data verification methods to study the resistance characteristics of plants and the characteristics and performance of trapped particles.At the same time,it studies the influence of tree planting in the street valley on the concentration of particulate matter under the combined influence of the two effects.The main research contents are as follows:(1)Apply numerical simulation method to analyze the influence of blade angle,leaf area density,and wind speed on the front and rear air resistance of the blade from a microscopic point of view,observe the changes in the flow field of the air flowing through the blade,and calculate the flow resistance difference between the front and rear of the blade.The resistance expression and the resistance coefficient expression in different wind speed ranges are given.The results show that when the wind speed is small,the pressure difference has a linear relationship with the wind speed.As the wind speed increases,the pressure difference and the speed have a quadratic relationship,and the flow resistance difference It is more affected by wind resistance and leaf area index.(2)Apply numerical simulation and based on similar theories to study the effect of plant leaves on the collection efficiency of particulate matter,and give pre-tests of the collection efficiency of single and multi-leaf under different mechanisms.At the same time,according to Zhang’s theory,renew Considering the part of trapping efficiency,a more reasonable calculation formula for dry deposition rate is given.The results show that the collection efficiency is related to the particle size,windward angle,wind speed and leaf area density.The data is closer to the prediction result of the dry deposition rate.(3)From a macro perspective,FLUENT is used to simulate the effect of planting trees in vertical winds down in a street valley with a 2:1 aspect ratio on the concentration of particulate pollutants.The influence of trees on particulate matter is reflected in the pneumatic and sedimentary effects,in which the resistance coefficient and sedimentation velocity are taken into account through UDF,and the effects of each effect under the two planting methods on pedestrian height and concentration of pollutants at the building walls are analyzed and discussed,while recommending the most effective planting methods.The results show that tree planting has a positive effect on the removal of the concentration on the windward side and at the pedestrian level.With the increase of the differential pressure resistance coefficient,the concentration on the leeward side of the street valley increases.