Boundary Layer Effect And Resistance Characteristics Of Paste Pipeline Transportation

With the in-depth implementation of the national guiding policy for building green mines,filling mining method has been widely used.Mine solid waste paste filling technology is the main supporting technology of green mining,in which pipeline transportation technology is the core of paste filling,which is very important to mine production.However,at present,in the calculation of resistance loss along the pipeline,the paste in the pipeline is generally regarded as a completely homogeneous body with the same everywhere,and the paste boundary layer effect and its influence on the resistance under the actual pipeline pressure are not considered.Boundary layer effect is a basic property of high concentration slurry,which together with rheological properties governs the flow performance of slurry.There are many factors affecting the boundary layer effect,such as temperature,particle size and gradation,solid concentration,yield stress,wall roughness and wall shear stress.In fact,due to the boundary layer effect,the paste has a radial rheological parameter gradient under the condition of pipeline transportation,which is particularly obvious in the mixed paste of coarse and fine aggregate.Starting from the pressure bleeding effect of paste,this paper carried out pressure bleeding test and rheological test,combined with the stress analysis of coarse and fine particles in the process of paste pipeline transportation,constructed the calculation formula of resistance loss along paste steady-state pipeline transportation considering boundary layer effect,and verified the reliability of this model through industrial application.The main research contents include the following:(1)Combined with the pressure bleeding effect and particle accumulation effect of paste slurry,the prediction model of pressure bleeding rate of paste slurry was established.On this basis,considering the wall attachment effect of particles,the wall attachment coefficient of particles under close packing and universal conditions is calculated.It is concluded that the thickness of static wall loss boundary layer is a function of solid filling degree and average particle size of paste slurry,and an estimation method of static wall loss boundary layer thickness is proposed.(2)The gradient evolution model of rheological parameters in the radial direction of the pipeline during the steady-state pipeline transportation of paste slurry is established.Through the stress analysis of the internal particles in the steady-state pipeline transportation of paste slurry,the radial motion trajectories of coarse and fine particles and water in the pipeline are obtained.Using ANSYS fluent as a tool,it can directly reflect the distribution of particles in the paste in the radial direction of the pipeline.The rheological parameters of paste slurry at different positions in the radial direction of the pipeline were measured by rheological test.Regression analysis was carried out on the test results,and the regression parameters were compared with the rheological parameters before and after the pressure bleeding test of paste slurry,so as to build the gradient evolution model of rheological parameters in the radial direction of the pipeline during the steady pipeline transportation of paste slurry.(3)The thixotropic test of paste slurry was carried out,and the thixotropic laws of yield stress and plastic viscosity of paste slurry were obtained;The formation process of boundary layer at the inlet of paste slurry pipeline transportation is studied,and the migration law of coarse and fine particles and water in the paste at the beginning of pipeline transportation is obtained.Then,the evolution law of paste slurry yield stress and plastic viscosity at the initial stage of pipeline transportation is calculated,and a three-dimensional evolution model of paste slurry yield stress and plastic viscosity at the initial stage of pipeline transportation is established.On this basis,a method for estimating the transient boundary layer thickness of paste slurry pipeline transportation is proposed.(4)Through the stress analysis of internal mass point in the process of paste slurry pipeline transportation,combined with the continuity equation,the differential equation of motion and the constitutive model of Bingham fluid.The radial gradient of yield stress and plastic viscosity is added.Thus,the differential equation of paste slurry pipeline transportation considering boundary layer effect is derived.(5)Combined with the regional distribution characteristics of Bingham fluid pipe flow,the radial gradient model of yield stress and plastic viscosity is added,and the calculation formula of resistance loss along paste slurry pipe transportation considering boundary layer effect is derived;The new model considers the boundary layer effect of paste slurry pipeline transportation,which makes the calculation results more accurate than bukingham equation;Through python programming language,the calculation program of paste slurry pipeline transportation resistance model is compiled,which improves the convenience of the paper's model.The research results further improve the paste transportation theory,provide theoretical support for the paste filling technology of mine waste rock tailings,and are of great significance for the wide application of this technology.