Study On The Mechanism And Properties Of High-concentration Multi-sized Slurry Pressure Drop In Transport Pipeline

A reasonable theoretical foundation is needed for multi-sized particulate high density slurry pipeline transport in order to reduce the energy consumption and improve the conveying efficiency in commercial application,since the existing theories and models can't accurately predict the pressure drop of high density slurry transported by pipeline due to the restriction of its basing on single theory or experimental data.In response to this situation,this paper introduces the main research results and research status of the theoretical research and numerical simulation of slurry pipeline transportation.The applicability of the existing calculation model and the disadvantages of the present dredging engineering,such as complex slurry and high density conveying,are analyzed.The key scientific problems and main innovation points of the study on the resistance mechanism and characteristics of slurry pipeline transportation are presented.The variation of the flow regime of the high-concentration pipeline with different distribution particulate slurry and the composition and the mechanism of the pipeline resistance of each flow regime are researched.Also,the influence of slurry parameters such as slurry flow velocity,slurry concentration,particle size distribution and particle diameter on the resistance mechanism and properties of high density slurry pipeline transport is studied by means of theoretical analysis,experimental study and numerical calculation.A model,which can cover the industrial application flow range of high density slurry pipeline transport,including all flows regime from fixed bed to homogeneous,taking into account the multi-sized particulate,particle diameter and other particle characteristics,will be established.In particular,the model can accurately predict the high density slurry pipeline transport resistance.Expand the slurry pipeline transport theory,and provide basic theoretical and technical support for high conveying efficiency,low energy consumption transport of dredging and deep-sea mining.The main contents are as following:The flow velocity and solid concentration distributions of solid–liquid?slurry?flows transported by pipeline are investigated using a steady three-dimensional?3D?hydrodynamic model based on the kinetic theory of granular flow.Slurries of varying solid particle concentration,grain diameter,and flow conditions are studied,and the effects of particle–particle and particle–wall collisions and near-wall lift force on the concentration distribution are modelled.The simulation agrees well with various experimental results in the literature.The simulation shows that the solid concentration decreases rapidly near the pipe wall due to collisions with the wall.Fine particles smaller than the thickness of the viscous sublayer are most concentrated near the pipe bottom(maximum concentration at the relative location y_max/D?0.02D,where D is the pipe diameter)in the viscous sublayer,while the greatest concentration of coarser particles is away from the pipe bottom(y_max/D?0.1D),outside of the viscous sublayer.A steady-state three-dimensional multiphase hydrodynamic model based on the kinetic theory of granular flow is developed to investigate the distributions of solid concentration,flow velocity,granular pressure,and wall shear stress in multi-sized slurry?two particle sizes,d_p=0.125 mm and 0.44 mm,equal fraction by mass?transport by pipelines?D=54.9 mm?.The trends of the variation in transport properties with varying efflux particle concentrations?Cvf=20%,30%,40%,and 50%?and flow velocities?v=2,3,4,and 5 m/s?are studied,and the effects of other different-sized particles on characteristics are modeled.Simulation results agree well with the corresponding experimental results in literature.The simulation results show that coarse and fine particle phases have different characteristics in each operating condition.The degree of deviation of the characteristics of different-sized particles increases as solid concentration or mixture velocity decreases.Additionally,the distinct effects of near-wall lift force and particle–wall collision on the characteristics of different-sized particles in multi-sized slurry are observed.Three types of slurries?two single-sized glass-bead slurries 0.44 mm and 0.125 mm in diameter and a multi-sized mixture containing the two sizes in equal fraction by mass?transported by a 54.9-mm-diameter horizontal pipe are modeled using a steady three-dimensional hydrodynamic multiphase model based on the kinetic theory of granular flow.The effect of interaction of particles with different sizes on particle kinetics—such as particle concentration distribution,velocity distribution,granular pressure distribution,wall shear stress distribution,flow regime,and their change trends—are investigated for particles of different sizes for varying efflux solid concentration and flow conditions in a multi-sized slurry by comparing it with those in single-sized slurries under the same conditions.The results reveal the different transport properties and regularly changing trend of equal-sized particles in multi-sized and single-sized slurries under the same conditions with varying solid concentrations and flow velocities.Additionally,a lubrication layer forms from fine particles near the bottom of a multi-sized slurry,which is a key factor affecting the performance of coarse particles especially at low flow velocity,and changes the coarse particles'flow regime from saltation to a sliding bed,thereby reducing the collision energy consumption and pressure drop.Also,with high flow rate and high concentration,the addition of coarse particles weakens the turbulent intensity,reduces the impact between particles and turbulent dissipation force,and effectively reduces the additional pipe resistance caused by fine particles.The mechanism and degree of influence of the particle size variation in different flow conditions on the pipeline resistance was investigated.The interaction between the differently sized particles in the graded slurry was also examined.Furthermore,a new model called the Shanghai Jiao Tong University high-concentration multi-sized slurry pressure drop?SJTU-HMSPD?,which is based on the particle size distribution and multi-regime slurry resistance in pipeline transport throughout the flow velocity range,was developed and is presented in this paper.The SJTU-HMSPD is more suitable for calculating the pipeline transport resistances of complex graded slurries,and the calculation results agree well with the experimental data.Based on the calculation model of pipeline resistance,named SJTU-HMSPD,the calculation model of the energy consumption rate of the conveying unit volume particle materials is established for the uniform coefficient 1.26⁸.00,median particle size0.075mm⁴mm,particle volume concentration 10%⁶0%and pipe diameter0.203m⁰.800m slurry transport system.And then,the influence of parameters such as particle uniform coefficient,median particle size,pipe diameter,and particle volume concentration on the energy consumption rate is analyzed and verified by the published experimental data,the results show that the calculated value is in good agreement with the experimental data.The results show that the particle volume concentration of minimum energy consumption of the narrow-graded particles is about 30%,and the conclusion is consistent with the published conclusion.However,it is found that in the broad-graded slurry,similar medium-value particle size with narrow-graded,the particle volume concentration of the minimum energy consumption are larger than the particle volume concentration of minimum energy consumption of the narrow-graded,the Sand3 volume concentration of minimum energy consumption is nearly 50%.In addition,the calculation results show that when the diameter of the pipe is larger,the key velocity of slurry is larger,which is consistent with the current critical velocity calculation model.