Study On Dynamic Wetting Behavior Of Droplet Impact On Coal Dust Surface

The dust problem caused by coal resource mining affects the life and health of workers and the safety of coal mining seriously.As one of the most effective ways in mine dust removal engineering,spray dust removal is widely used worldwide.Spray dust removal includes the dust suppression method in which the dust on the coal rock surface or in the gap is wetted by the fog droplets to make it adhere to the coal rock surface.And,the dust collection method means the interaction between the fog flow and the dust in the air to make dust itself settled.Based on the "Wenzel type" and "Wenzel-like type" wetting theories,experimental analysis and numerical simulation methods were used in this thesis to deeply study the static and dynamic wetting characteristics of droplet on the surface of coal dust under different physical and chemical properties of droplet and coal dust as well as environmental conditions,which brings enlightenment to improve the dust suppression and dust collection mechanism and improve the dust removal efficiency of spray.The main research contents are as follows:(1)Conducting experiments to analyze the physicochemical properties of dust suppressant liquid and coal dust.The moisture,ash,volatile matter,fixed carbon content,particle size distribution characteristics,and surface roughness of three types of coal dust(YM80,WY80,WY200)were measured using industrial analyzers,particle size analyzers,and 3D profilers;The density,surface tension,and viscosity of the six solutions(deionized water,SDBS,AEO9,205 PVA,217PVA,224PVA)were measured;The static contact angles of six solution droplets on three types of coal dust surfaces were obtained.Regression equation for the static contact angles of droplet on the surface of coal dust with respect to various parameters through multiple linear regression analysis was eatablished.Through Spearman correlation analysis,the key factors affecting the static wetting characteristics of droplet on the surface of coal dust were identified.(2)Visualization experiments were conducted of six kind of solution droplet impacting on three types of dust piles.High speed cameras were used to capture the morphological changes and dynamic behavior of droplets during the spreading process on the dust pile surface through a self-made experimental system.MATLAB software was used to post-process the experimental images and analyze the changes of droplet spreading coefficient and center height coefficient over the time during the droplet impact on the coal dust surface.Thus,the effect of the physical and chemical properties of droplets,coal dust,and impact velocity on the morphological characteristics of droplets impacting behaviour as well as the droplet spreading coefficient were obtained.The maximum spreading coefficient model of the droplet impinging on the dust pile surface was proposed by fitting the function of the maximum spreading coefficient of the droplet with the change of velocity,Weber number and Reynolds number.(3)A numerical simulation model of droplet impact on dust pile surface was established based on the VOF coupled CSF model though ANSYS Fluent software.By establishing a numerical simulation model under the same conditions as the experiment,the experimental and numerical simulation results are compared and analyzed to verify the effectiveness of the model.By setting different operating conditions such as droplet surface tension,viscosity,coal dust roughness,wettability,and impact velocity,the variation patterns of droplet spreading morphology and maximum spreading coefficient under the influence of various parameters were studied.Through SPSS multiple linear regression analysis and Spearman correlation analysis,the regression equation and key influencing factors for the maximum spreading coefficient of droplet impact on dust pile surface were obtained based on various parameters.(4)Establishing a numerical simulation model of droplet impact on spherical dust particles,and analyzing the effect of droplet surface tension,viscosity,size,droplet to particle size ratio,particle roughness,wettability,and impact speed on the change of morphological and maximum spreading coefficient.Revealing the internal mechanisms of droplet rebound,fragmentation,and other morphological behaviorss.The regression equation and key influencing factors for the maximum spreading coefficient of liquid droplets impacting the surface of spherical dust particles were proposed through SPSS multiple linear regression analysis and Spearman correlation analysis.This thesis contains 109 images,33 tables,and 97 references.