Studies Of Dynamic Characteristics For Micro-particle Impact On A Flat Surface

The deposition of micro-particles plays an important role in daily life and various practical intustrial applications.Being the underlying physics of the deposition phenomena,the impact of a particle on a plane surface has received more and more attentions.There have been a lot of investigations on the particle-surface impact all over the world.However,for smaller particles(micro-particles),the inelastic dynamic characteristics for the impact of a particle with a plane surface have not been well studied.Particularly,the predictions of rebound characteristics for the impact of fly ash on a stainless steel surface have been rarely reported.In this study,the impact of a micro-particle on a flat surface are deeply and systemematically investigated through experiments and theoretical analysis.Firstly,the normal impact of a silicon dioxide particle on a flat stainless steel surface is experimentally studied.The temperature of the airflow and plane surface varied within the range of 20??160 ?.The variation of normal restitution coefficients with the incident velocity under different temperature conditions have been obtained using the high speed camera technique.The effects of temperature,particle diameter and incident velocity on the rebound characteristics of the impact are investigated.In the force analysis,the rationality of ignoring the thermophoretic force and drag force are justified.The critical velocities under different experimental conditions are predicted by the dynamic model with the fitted damping coefficients.Secondly,based on the modified Hertz theory,allowing for energy dissipation due to plastic deformation,combining with the Newton's law of motion,a more rigorous multi-stage dynamic model has been developed to describe the rebound behaviour of the normal elastic-plastic impact of micro-particles against a plane surface without adhesion.Then,the effects of material properties on fraction of energy loss,the dynamic parameters and the variation of normal restitution coefficient during the impact are predicted.Furthermore,the predictions of both normal restitution coefficient and contact time agree well with the experimental results.Thirdly,based on the extended JKR model of adhesion,a dynamic model has developed to describe the rebound behavior of the normal impact of elastic-plastic adhesive spheres.The surface adhesion affects both the loading and unloading stages.The force,deformation,contact time and motion of particle can be predicted by the present model.In addition,attempts have been made to establish the expressions of normal restitution coefficient and critical capture velocity.The models were validated by comparison with experimental results in literature.Lastly,the oblique impact of fly ash onto a plane stainless steel planar at room temperature is experimentally studied.The effects of both incident velocity and incident angle on the rebound characteristics are investigated.Based on the developed classical rigid body theory,the critical incident angle between gross sliding and no-sliding is 60 degrees.Then the coefficient of kinetic friction between fly ash and stainless steel is determined to be 0.6.Then the fitted expressions of dimensionless tangential restitution coefficient,tangential rebound velocity at the contact point,and the dimensionless rebound angle are established.It provides a reliable basis for quantitative study of particle-surface impact in gas-solid two-phase flow.