Transport Characteristics And Capture Technologies Of Fine Particles In Open And Enclosed Spaces

In recent years,haze has become an important form of air pollution.The study on the transport characteristics of the fine particles and then put forward the prevention measures.is of great significance for improving the environmental air quality and protecting the health of the human body.This article mainly focuses on the roadside and the indoor environment.The diffusion and transport process of fine particles in open and enclosed space is explored.The filtration performance of fiber filter for fine particles is investigated.The main contents of the study include the following parts:Firstly,the typical roads and their surrounding areas in the city are taken as research objects.By using the combination of experiment and numerical simulation,a coupling model of meteorological factors and vehicle exhaust emission characteristics is established.And the influence of exhaust gas on air quality in roadside building environment is revealed.In addition,based on the average particle concentration on the road,a particle transport model in roadside building environment is established to explore the influence mechanism of roadside obstacles on particle diffusion.The results show that the wind direction has a significant effect on the concentration distribution of particles in the street.Under the parallel wind direction,the concentration of particles inside the street is relatively low.While the vertical and inclined wind direction tends to cause particles accumulation in the streets.Besides,higher sulphuric acid and organic vapor emissions will promote nucleation process and the nuclei particles will grow up quickly,thus pollute the environment.Therefore,we need to strictly limit emissions of sulfur dioxide and organic vapor from exhaust gas.The noise barriers can block the airflow and restrict the movement of particles to the downstream region,resulting in a lower concentration of indoor particles.In contrast,the roadside vegetation is not effective to limit the diffusion of particles,even though it can block the airflow.Vegetation in front of buildings is also easy to cause particles to gather near buildings.Increasing the particle deposition velocity on vegetation can reduce indoor particle concentration.The above results revealed the impact of vehicle emission sources on air quality in roadside micro-environment and quantified the contribution of the exhaust to the haze weather.All the conclusions are helpful to relevant departments to formulate vehicle emission reduction policies and road design standards.Secondly,the particle concentrations of indoor and outdoor are monitored by optical aerosol size spectrometer.At haze day,the concentration of outdoor particles is about 2 times as much as that of indoor environment.The number concentration of indoor and outdoor particles mainly concentrated in the range of dp?0.25 m.Only by closing doors and windows can't effectively restricting outdoor particles to penetrate into indoor environment.Thirdly,the influence of outdoor particles on indoor air quality during single-sided natural ventilation is studied by drift-flux model.The transport characteristics of fine particles from outdoor to indoor environment are revealed under different wind directions and speeds.The deposition fluxes of particles at different room surfaces are quantified.The results showed that smaller particles dispersed more evenly in the indoor environment,while the larger particles are distributed in a stratified state.Wind direction and wind speed have little effect on the deposition flux of particles on the surfaces of the room.The deposition flux of small particles on the ceiling is three orders of magnitude higher than that of large particles.In addition,with the increase of wind speed,the influence of wind direction on indoor particle average concentration is more obvious.Fourthly,the Lagrange particle tracking model was used to investigate the effect of different position,the direction of the air outlet and the clean air deliver rate(CADR)of air cleaner on the purification of uniformly and non-uniformly distributed particles in the indoor environment.The results indicated that the concentration of indoor suspended particles can be reduced rapidly by using larger CADR.When the amount of CADR is small,the effect of air cleaner positions will increase.The downward air supply tends to form the "air loop",which is not conducive to the purification of particles.In addition,the research on smoking and cough process shows that the closer the purifier is from the human body,the faster the indoor suspended particle concentration will decrease.Finally,the particle movement in the elliptical fiber filter media is studied by numerical method.The filtration efficiency of irregular arranged elliptical fibers for fine particles is explored.The influences of different aspect ratio,surface velocity and solid volume fraction on filtration efficiency are revealed.Generally,increasing the effective collision area of filter material can significantly improve the filtration efficiency.When solid volume fraction is high,the filtration performance of stout elliptical fiber is stronger than that of round fiber.Under various conditions,slender fiber can significantly enhance filtration efficiency of filter media.However,the quality factor of elliptical fiber is relatively low.This research is of great significance for improving the filtration performance of fiber filter in practical engineering.