Study On Distribution Of Heavy Metal Particles In Subway Braking Process

The degree of particulate pollution in urban subway stations is an important index of the city environmental quality evaluating.Due to the wear of iron and steel in the process of running and braking,the heavy metal elements in the air particles of the subway show obvious enrichment characteristics,and these particles have higher toxicity than outdoor atmospheric particles.The subway braking process occurs at the arrival time of the train,and the heavy metal dust generated by the brake shoe wear will move to the platform with the piston air,which will affect the air quality of the platform and the passengers' health.In this context,it is urgent to study the concentration and distribution characteristics of particulates produced by the braking process of Metro trains.This paper takes the particulate matter generated by subway braking process as a research object.The theoretical model of particle diffusion was established to simulate the diffusion process of particles,and the main factors affecting particle distribution were analyzed.The CFD simulation of braking process of metro train is carried out based on field investigation and literature data,Under the premise of validation of numerical simulation results,the composition,concentration and distribution of particles in different planes under different working conditions were analyzed and discussed.The 3D visualization images are generated on the Matlab plane grid,and the concentration distribution of the particles in the special plane is visualized and compared,the main factors affecting the concentration distribution of particles are also found out in the paper.The variation curve of the particle concentration with the influence factors was fitted by the least square method,and using the curve to predict the concentration distribution of particles during train braking.The mass concentration data of the simulated particles were processed,the exposure assessment of particulate matter and the risk calculation are based on the health risk assessment system,to explore whether the particulate matter produced by the braking process of subway vehicle will harm the health of passengers on the platform.In the process of simulation and research,the main conclusions are asfollows:(1)Set the screen door will greatly reduce the particle concentration in the subway platform;Change the gas initial braking speed will also have a certain impact on the concentration of the subway platform particles size;Replace the brake materials will hardly change subway platform particles value.(2)The setting of screen door has a great influence on the distribution range and regularity of the particle in the subway platform.But the change of air brake initial speed and brake shoe material have little influence on it.(3)The fitting equation of the subway platform's horizontal distance and particle concentration is three times curve,and the fitting equation of initial velocity and particle concentration is two times curve.(4)There is a positive correlation between particulate matter exposure and mass concentration of particulate matter.The amount of particles ingested through the mouth > the amount of particles ingested through skin contact > the amount of particulate inhaled through the nose.The exposure of children to particulate matter was significantly greater than that of adults.(5)There was a positive correlation between exposure risk and exposure,oral intake has the greatest risk of exposure.Children face greater health risks than adults.In addition,there is a carcinogenic risk of nickel,which has a serious negative effect on human health.