Research On Particle Migration Characteristics Of Solid-liquid Two-phase Flow In A Slurry Transport Pump For Deep-sea Mining

The mineral resources contained in the deep seabed are rich in reserves,and its huge development prospects have become the key excavation objects in the world.At present,the mainstream lifting method in deep sea mining is the pipeline hydraulic lifting system,which transports seabed minerals to the sea surface.The slurry pump is the core equipment of the deep-sea mining system,providing the lifting force required to lift the ore from the seabed to the sea surface,so the safety and efficiency of the conveying performance in the slurry pump are very important.The passing characteristics and complex motion characteristics of the solid-liquid two-phase flow in the pump are the key factors that determine the safety and efficiency of the slurry pump.Therefore,this paper focuses on the slurry pump used in deep sea mining,and analyzes the influence of different factors on the solid-liquid two-phase flow and particle migration characteristics.In this paper,the CFD-DEM coupling method is used to analyze the flow characteristics,particle distribution,and passing characteristics of the slurry transport pump;based on the pump design theory,the influence of the impeller channel inlet and outlet area ratio on the particle transport characteristics is studied;Two-phase flow characteristics and slip velocity characteristics of the pump under the condition of different particle sizes.The main research contents and conclusions are as follows:(1)The design,experimental comparison and numerical calculation of the slurry pump are completed.The accuracy of the calculation method in this paper is verified by comparing the experimental results of the external characteristics of the two-stage slurry pump with the numerical calculation results.(2)The flow characteristics of the two-phase flow in the two stages of the slurry pump are studied.There are differences in the flow characteristics of the two-stage impellers.Compared with the first stage,the velocity distribution of the second-stage impeller is disorderly,and the vortex distribution increases to the impeller inlet,but the flow Line disorder and omega vortex fragmentation intensified.There are vortices in the guide vane of both stages,and there is a low-pressure area on the suction surface pressure of the blade.The vortex distribution in the two-stage guide vanes is generally similar,and the degree of fragmentation in the second stage is intensified.The total number of particles in the pump tends to a dynamic equilibrium after 0.5s,the second stage has better passing ability than the first stage,and the kinetic energy of particles changes limitedly with the number of stages.The particles in the inlet area of the impeller are crowded and the speed is low.After entering the impeller,the particles are accelerated and move along the pressure surface to the outlet.The particle speed and trajectory of the two-stage impeller are similar.The movement state of the particles in the first and second guide vanes is similar,mainly moving along the suction surface of the guide vanes.(3)The effect of different impeller channel inlet and outlet area ratios on the particle transport in the slurry pump is studied.With the increase of the impeller inlet and outlet area ratio,the pump head increased but the efficiency decreased;Vortex and a lowvelocity zone appears at the trailing edge of the blade suction surface and gradually increases.The low-pressure area near the impeller inlet is reduced,the high-pressure area at the impeller outlet is reduced,and the vortex in the outlet area is broken,which aggravates the flow instability and affects the particle movement.As the impeller inlet and outlet area ratio increases,the position of the particles leaving the impeller moves from the back section of the blade to the middle position,the number of high-speed particles at the outlet increases,and the trajectory is smoother and reduces collisions when leaving the impeller,which is conducive to particle movement.The particle passing time increases first and then tends to be stable with the ratio,but the standard deviation first increases and then decreases.The passing time distribution of model pump 3 is stable,and the particle passing time of the first and second impellers is increased by 5 % and 7 % respectively.Too large ratio has a negative impact on the particle passing time in the impeller.(4)The flow characteristics of the two-phase flow under the condition of different particle sizes in the slurry pump are analyzed.The particle size has limited influence on the hydraulic performance of the slurry pump under the condition of low concentration.Small particles have better fluid followability and are easier to distribute and move closer to the pressure surface of the blade.The distribution of large particles is relatively scattered,and the fluid followability of large particles is worse.The particle size has a certain influence on the energy conversion efficiency of the guide vane,the smaller the particle size,the higher the energy conversion efficiency.The time for particles to pass through the slurry pump increases with the particle size.The particle slip velocities of the three particle sizes are similar in overall variation trend.In the first-stage impeller,the slip velocity increases with the same magnitude in the range of 10-50 mm.Affected by the better fluid followability of small particles,their slip velocity is greatly reduced at the outlet of the impeller.In the guide vane,the slip velocity decreases with the decrease of particle size,indicating that the speed of small particles in the guide vane decreases less than the fluid velocity.The zero position of the slip velocity moves to the left as the particle size decreases,and the particle velocity exceeds the fluid velocity at this time,which is beneficial to the transport of subsequent particles.