Studies on Suspension of Particulate Matter from the Ground Surface (II)

Simulation of particle suspension

Abstract

Motions of a particle after it starts to move on a wall surface may be classified as sliding/creeping on the surface, saltation from the surface, and suspension in the fluid body. Among these three motions, suspension is considered to be the most important mechanism from the view point of air pollution. Initiation of suspension is mainly due to either detachment by collision after creeping motion, or detachment by lift-up. In order to simulate these phenomena, systematic models which incorporate these two initiation mechanisms and Lagrangian diffusion were developed and evaluated. Lagrangian velocity which affects on the motion of particle is expressed by the first order Markov process in the models. Only viscosity term and gravity term are included in the equations of motion for spherical particle. A set of hypothetical physical characteristics of a particle were assumed for the investigation.
It was shown by comparing numerical solutions of the Lagrangian diffusion model with analytical solutions for concentration distribution expressing diffusion in shear flow that the Lagrangian diffusion model is rationally representative of characteristics of particle suspension.
The two models for initiation mechanisms of particle detachment from wall surface were investigated by utilizing experimental data obtained from particle suspension experiment conducted with a pile of coal because wind speed data and total estimated amount of particles suspended were available. The bound detachment model was found to show better agreement with the experimental data than the lift-up detachment model. This result appears to be rational because repellent detachment phenomenon was expected to be predominant in the experiments due to relatively large sizes of coal particle.