Theoretical Analysis And Numerical Simulation Study Of Particle Pollution In Subway Environment

With the acceleration of urbanization process in China, the problem of urbantraffic congestion becomes more and more serious. Metro transport systems in majorcities around the country came into being. Subway traffic increased year by year, andresult in shorter train headways and increase the number of trains. Because of itsconvenient, efficient and comfortable features, which inevitably cause a decline in thequality of the air inside the subway station, the health of passengers and subway staffis harmed. The phenomenon of discomforting or even fainting passengers hasoccurred in some parts of the city subway. Therefore, the study of metro stations’environmental issues becomes particularly important.In this paper, lumping parameter model, basing on mass balance equations, therelationship between the different systems in the form of air conditioning, screendoors’ open conditions and the concentration of particulate matter in subwayenvironment is derived and the outdoor concentration of particulate matter, the initialconcentration of indoor particulate matter, the filtration efficiency of filtrationsegment, the penetration wind capacity of entrances and exits, the number ofpassengers, the second suspension and other factors on the concentration ofparticulate matter are analyzed. The outdoor concentration of particulate matter, theamount of dust the station hall site, particulate matter’s sedimentation rate, the initialconcentration of subway, the method of determining amount of air leakage are given.Taking a subway station in Xi’an as the research object, establishing a full-sizethree-dimensional geometric model according to actual engineering design data, usingthe size of mesh function method, a mixture model as a mathematical simulationmodel, taking the actual test data as a boundary condition, the station public areas velocity field, temperature field, particle concentration distribution are simulated andanalyzed by the application of Fluent software, and actual test results were analyzedto verify the accuracy of the simulation. The variation relationship between PM10,PM2.5, PM1.0concentration and height, and PM2.5/PM10, PM1.0/PM10ratio are studied.Finally, seven kinds of particle concentration distribution conditions are analyzed andthe concentration distribution of particles of two different airflows is analyzedcomparatively.The author of particle concentration distribution in public areas metro istheoretically analyzed and numerically simulated by author, the following are themain conclusions:(1) On the plane1.4m from the ground floor of the station hall theconcentration of particulate matter below the outlet is low. The concentration of PM10is about138μg/m3; the PM10concentrations of both sides back to the area of near thebottom of the outlet, the station hall, ticket vending machines and entrance gates, etc.are high, especially near the vending machine. The concentration of PM10pollution isvery serious. On the plane1.4m from the ground, the outlet concentration ofparticulate matter is about112μg/m3; There exists a vortex region, the concentrationof particulate matter is higher. Pollution is more serious; escalators and facing awayfrom stairs outlet side, the concentration of particulate matter of daily averageconcentration of respiratory particulate matter is higher, the maximum is364μg/m3,more than the " Metro Design "(GB50157-2003). It should be less than the specifiedrequirements250μg/m3.The pollution in the region is serious.(2) For PM2.5, PM1.0. In the concourse level, except the both ends of theconcourse, near the vending machines, near high entrance gates near the concentrationof particulate matter is higher. Other regional concentration distribution is moreuniform; on the plane at a distance of1.4m from the concourse level ground, themaximum concentration of PM2.5is99.4μg/m3; the maximum concentration ofPM1.0is72.4μg/m3. On the plane from1.4m at the platform layer; the maximumconcentration of PM2.5is140μg/m3; the maximum concentration of PM1.0is72.9μg/m3.(3) Whether the platform layer or station hall, PM2.5/PM10ratio is greater than 0.5, the maximum value is0.86.PM1.0/PM10ratio is higher.(4) In the seven kinds of simulated working conditions, the optimal workingcondition is the second one. After changing the airflow, the particulate matterconcentrations of concourse level, site level of the height of the plane crowd breathingwere significantly decreased.