The Investigation Of Particle Detachment Resuspension And Dispersion Due To The Rotating Wheel

Recently,the environmental pollution caused by suspended particulate matter in the air and their subsequent harm to people's lives and production has attracted increasing attention.As one of the most important means of transportation for people,motor vehicles during driving are an important source of particulate pollution.The rotating wheels are the most important factors causing suspended particulate matters.Therefore,the particulate matters caused by the rotating wheel are studied through a combination of theoretical and experimental investigation in this paper.This paper deeply explores the mechanism of particle detachment and suspension caused by the wheel rotating movement;investigates the dispersion of particulate matters around the rotating wheel,analyzes the related influencing factors;explores the emission factors caused by wheels under different conditions.This paper provides a theoretical and experimental basis for revealing the main influencing parameters of particulate pollution and clarifying each influencing parameter's contribution.In summary,the research of this paper can be summarized in the following aspects:(1)Research on the detachment and suspension model of particulate matters detached from the ground caused by the rotating wheel.In this paper,the detachment and suspension modes of particulate matters under the influence of wheel rotation are divided into two types:one is that the particulate matters are directly detach and suspend from the ground;the other is that the particulate matters adhere to the wheel surface first,and then detach and suspend from the wheel surface.After analyzing the forces acting on particles adhering to the ground,this paper finds that adhesion force and hydrodynamic force are the main forces that determine whether particles could detach and be suspended from the ground.In this paper,through the force moments analysis of the particulate matters on the ground,the model of particulate matters detach from the ground is constructed according to the rolling detachment method,and the suspension model of particulate matters is constructed according to the force balance method.(2)Research on the particulate matters migration model and detachment and suspension model from the wheel surface.A contact migration model of particles from the ground to the wheel surface is constructed.For the particles adhered to the wheel surface,the detachment and suspension model from the wheel surface is further constructed.Through a self-designed and built particle detachment and suspension test bench,it is found that the critical particle size for detachment and suspension of Al₂O₃ and Si O₂ particles was reduced from 60?m to 26?m,and from 57?m to 31?m,respectively,in the range of wheel rotation speed from 2m/s to 7m/s.By comparison,it is found that the deviation between 90%of the model calculation results and the experimental measurement results is less than 20%.Therefore,the model constructed in this paper can better predict the critical particle size of detachment and suspension.The study also finds that for the particles that adhered to the wheel surface,the gravity force moment changes with the position of particles,and the influence for detachment and suspension cannot be ignored.In addition,influencing factors such as wheel rotation speed,surface roughness,and particle characteristics will affect the critical particle size of detachment and suspension by changing the force moment acting on particles.(3)Investigation on the mass distribution and emission factors of particulate matters scattered around the wheel.This paper experimentally investigates the mass distribution of particulate matterrs near an isolated rotation wheel in a deliberately designed setup.The results show that in the area of 1.5R behind the wheel,1.9B on the side of the wheel,and 0.5R in the height direction,the mass of particulate matters increases significantly with the increasing particulate matter deposition,wheel speed and wheel-conveyor pressure.Based on the above investigation,the emission factor(the total mass of particulate matter emissions caused by each wheel driving 1km)is calculated.Through the fitting results,it is found that the emission factor shows a linear increase with the increasing of particulate matter deposition.The emission factor increases with the increasing of wheel speed and wheel-conveyor pressure,and the growth rate change from fast to slow.(4)Investigation on the size distribution of particulate matters scattered around the wheel.In this paper,the quantity and mass percentage of PM_2.5 and PM₁₀ at each sampling point under different wheel rotation speeds are measured.The results show that the lowest percentages of PM_2.5and PM₁₀ are 19%and 61%,respectively.With the increasing of wheel speed,the mass percentage of PM₁₀ particles at the sampling point near the wheel will decrease.Therefore,large-size particles are an important factor affecting the mass distribution.The investigation also finds that the PM_2.5and PM₁₀ highest number has a law of gradually moving backward and upward as the speed increasing.This is due to the fact that the faster wheel speed is conducive to the diffusion of particles to higher and farther positions.(5)Simulation study of particulate matter dispersion caused by the rotating wheel based on experimental results.In this paper,the dispersion of particulate matter caused by the rotating wheel is studied by the simulation method.According to the emission factor and the particle size distribution measured and calculated in the test,this paper further optimizes the emission conditions of the particulate matters in the simulation study.The particle dispersion model that is more in line with the actual situation can be obtained.