Research On The Flow Characteristics Of Double-row Hydraulic Sluicing Method In Deep-sea Mining

The exploitation of marine mineral resources become more and more important with the rapid development of industry and the intensification of energy scarcity.However,the harsh and complex environment has brought difficulties for the exploration,and largescale commercial exploitation of the seabed is further hindered by some problems such as energy transfer.In the past decades,many researches have been conducted on the exploitation of deep-sea resource.In the mining of mineral resources such as manganese nodules,pipeline lift mining system is universally acknowledged as the most potential in practical application,which consists of a deep-sea mining vehicle,support vessel and lifting system.Among them,the collection mode of the deep-sea mining vehicle can directly affect the efficiency and energy consumption of the system.The selection of the collecting method and its structural design are particularly important.The hydraulic collection method is widely seen in the deep-sea mining vehicle,including suck-up-based method,Coanda-effect-based method and double-row hydraulic sluicing method.The double-row hydraulic sluicing method has significant advantages in collection efficiency and energy consumption,but its design is more complex.The unreasonable design of structure and flow field can affect the collection effect.And there are few studies on its flow field characteristics and particle motion characteristics.In this paper,the numerical simulation of solid-liquid two-phase flow in the doublerow hydraulic sluicing method is conducted,and the flow field and dynamics characteristics of particle in the device are studied.At the same time,the effects of nozzle flowrate and the angle between the nozzle and the ground on the device are analyzed.The contents and results of this project are as follows:(1)A double-row hydraulic sluicing structure with high pickup efficiency is designed,and its flow field and the dynamic characteristics of particle are analyzed by CFD-DEM(Computational Fluid Dynamics-Discrete Element Method)and DMD(Dynamic Mode Decomposition)method.It is pointed out that the upwelling in the pipe is related to energy conversion: the jet impinges on the ground to form a high-pressure area,which produces a large vertical pressure gradient in the central area,thus forming the upwelling.The front nozzle plays a drainage role,while the rear nozzle blocks the fluid and particles,which helps to form the upwelling.(2)The motion of different particles is analyzed.It is found that more than 95% of the collected particles will directly move to the outlet,while a few of particles will fall back when rising.The motion of particle consists of two main stages,that is rapid acceleration followed by slow deceleration.The slip velocity of particle and fluid forces on particle such as drag force,pressure gradient force and Magnus force are calculated.It is pointed out that the particles are greatly affected by the drag force and pressure gradient force before entering the pipe.After getting into the pipe,the drag force and pressure gradient force decrease rapidly,but still play a dominant role.With the height increases,the fluid force on the particles decreases and the particle velocity is stable.(3)The influence of jet flow on the device is analyzed.When the flow rate of front nozzle is low,the drainage effect is weakened and the upwelling position is forward.The particles in the mining area will further hinder the drainage effect and the fluid flows out along the front the device,which causing particles to be carried around.When the flow rate of the rear jet decreases,the blocking effect of the jet is weakened,and a large amount of fluid and particles flow from the rear device to the surrounding.(4)The influence of the angle variation between the jet and the ground on the collecting device is analyzed.The angle α between the front row jet and the ground has a significant impact on the device.When α decreases,the drainage effect of the front jet is weakened and the rate of upwelling decreases,and a large number of particles stay at the front of the device.When α increases,the upwelling position shifts forward,the flow rate in the pipe decreases,and a few particles stay at the front of the device.The angle βbetween the rear jet and the ground has a relatively small impact on the device.When βdecreases,the high-pressure zone formed by the impinging jet becomes closer,and the rate in the pipe increases,and the collection rate slightly decreases.When β increases,the blocking ability of the rear jet increases,but the upwelling is weakened and the collection rate decreases.Most of the particles that are not collected flow out from the left and right sides of the device,and some flow out from the rear of the ore collecting device.