Distribution Characteristics Of The Secondary Circulation In Spirals And Its Seperation Effect

As typical gravity processing equipments,the spirals are widely used in the fine coal and mineral processing industry.The internal reason why the spiral chute can separate useful minerals from gangue lies in the density and particle size difference between them and the external reason lies in the unique separation flow field in the spiral chute.As environment-friendly equipment,spiral chute has been paid more and more attention by people because of its advantages such as simple structure,no moving parts,clear ore separation and large handling capacity per unit area.Firstly,the flow characteristics of the fluid in the spiral chute with basic parameters were systematically simulated.On this basis,the influence of structural parameters on the flow field characteristics was explored by changing the ratio of distance to diameter and section shape,and the influence of structural parameters on the distribution characteristics of secondary circulation was discussed.Then,the mineral particles were simulated under the basic parameters,and the influence of the ratio of distance to diameter and the parabola index on the separation of mixed particles was investigated.The results show that:(1)With the increase of the number of flow coils,the transverse,tangential and axial velocities at the same radial position show an overall trend of increase.With the increase of the relative water depth,the inward transverse velocity first increases and then decreases,and then turns to outward and increases,and slightly decreases when approaching the surface of the water layer.The tangential and axial velocities increase gradually from the bottom of the groove to the surface of the flow film,and remain unchanged or slightly decrease when approaching the surface.Transverse velocity turning points are between 0.4 and 0.6 relative water depth.With the increase of the number of overflow cycles,the range and intensity of the secondary circulation gradually increase,and the flow field reaches a stable state at the end of the third turn of the spirals.(2)The Reynolds number of the fluid is positively correlated with the radial position on the whole,and slightly decreases near the outer edge region;With the increase of the number of flow cycles,the Reynolds number in the inner edge region increases as a whole.The Reynolds number in the middle region increases first and then decreases.The change of Reynolds number in the outer edge region is complicated.From the perspective of flow pattern range,with the increase of the number of flow cycles,the laminar flow range continues to increase,the transition flow range first increases and then decreases,and the turbulence range continues to decrease.(3)The ratio of distance to diameter has a great influence on transverse velocity.At the end of turn 1/2 and turn 1,the regularity of lateral velocity is not strong under different ratios.At the end of the third circle,with the increase of the ratio,the absolute value of the transverse velocity and the intensity of the secondary circulation at the same water depth tended to decrease.At the same radial position,the Reynolds number at the end of each cycle decreases with the increase of the ratio of distance to diameter.In addition,with the increase of the ratio of distance to diameter,the range of laminar flow is increased,the range of transition flow is basically unchanged,and the range of turbulence is decreased,which is conducive to the migration of particles in the inner edge region to a certain extent.(4)The influence of parabolic index on the secondary circulation is different at the end of different turns.In terms of intensity,with the increase of the parabolic index,the intensity of the secondary circulation at the end of the first and third cycles is more complex.At the end of the first cycle,the intensity of the secondary circulation tends to increase.From the perspective of range,the variation law of the range of secondary circulation is complex at the end of the 1/2 and 3 cycles.The increase of intensity and range of secondary circulation is beneficial to mineral stratification and zoning.The influence of parabola index on Reynolds number is complex.With the increase of parabola index,the laminar flow range expands,the transition flow range decreases,and the turbulence range increases first and then decreases.(5)Particles simulation results show that the radial discharging position of quartz and hematite particles is consistent with the actual process,and the addition of particles has a significant effect on the film thickness and the distribution characteristics of secondary circulation.When the ratio of distance to diameter was increased from 0.45 to 0.6,it is beneficial to the separation of mixed minerals of quartz and hematite.When the ratio of distance to diameter is increased from 0.6 to 0.75,it is not conducive to the separation of the mixed minerals.The decrease of parabolic index is also not conducive to the separation of them.