| The cyclone-static microbubble flotation column has significant advantages in fine-grain mineral sorting,and its internal flow state is more complicated than conventional flotation columns.Flow field characteristics are especially important for its sorting performance.In recent years,computational fluid dynamics numerical simulation technology and PIV measurement technology have developed rapidly and become the main method for studying flow field.However,due to the complexity of the flow,the research of the flow field has been carried out from the beginning of the invention to the current industrialization.But,neither the experimental measurement nor the numerical simulation is far from perfect and accurate,and it cannot reflect its complex multi-phase flow field characteristics,which affects our in-depth study of the flow field to improve its sorting environment and restrict its sorting performance.In this paper,we take small multi-fluid flotation column as the research object.Single-phase and two-phase PIV measurements and numerical simulation studies were carried out on the problems existing in the previous studies.The main research results and contents include the following aspects.The PIV complex flow measurement platform was built.The endoscopic technology was used to solve the problem that the conventional PIV technology could not measure the cross-section flow.Therefore,we designed an experimental scheme for tangential velocity measurement using a combination of a CCD camera and an endoscope with fluxes of 0.25 m~3/h,0.50 m~3/h,1.00 m~3/h,and 1.50 m~3/h.The measurement results show that the axial,radial and tangential velocities of the fluid are between-0.08 m/s and 0.08 m/s,0 to 0.2 m/s and 0 to 0.35 m/s at four circulating flow rates.Therefore,the flow in the column is dominated by tangential motion.At a distance of 300 mm(about 1.5 times the diameter)above the swirling inverted cone,the axial velocity exhibits a"?"-shaped distribution,and the fluid at the axial center moves upward.The axial velocity decreases rapidly along the radial direction to zero and then begins to move downwards and then slowly decreases to zero,following a movement up again up to the wall.There are two zero velocity points indicating that there are two opposite vortices in the axial direction inside the cylinder.It acts as a centrifugal motion in the radial direction,slowly decreasing from the axis to the wall.The tangential velocity increases rapidly along the radius and then slowly decreases.As the circulating flow rate increases,the values of the three velocity components increase.A turbulence model suitable for calculating the FCSMC cyclone field was established.The turbulence model of the cyclone field was verified by the relatively complete PIV experimental data of single-phase flow field,including the four turbulence models of Standard k-?,RNG k-?,Realizable k-?and RSM.The results show that the RSM model has the best agreement with the experiment,and can accurately predict the distribution trend of tangential,radial and axial velocity in the radial direction,and the average velocity deviation is close to 15%.Only Realizable k-?can predict the axial velocity,but the deviation is 78%.The prediction deviation of the remaining radial velocity and tangential velocity are both close to 30%.A gas-liquid two-phase PIV measurement platform with multiple fluid flotation columns was built.Simultaneous measurement of gas-liquid two phases in a complex flow state inside a flotation column is realized by using the split-band sub-band technology.A two-phase PIV measurement at a height of 200 mm and 400 mm above the swirling inverted cone was achieved with a circulating flow of 1.00 m~3/h and 1.50m~3/h.The results show that the bubble size in the experiment is mainly concentrated at 1mm,and the gas content is about 1%.The two-phase flow measurement liquid phase velocity is consistent with the single-phase flow measurement result in the axial velocity and radial velocity distribution trends.The single-phase flow test can and can only represent to some extent the motion characteristics of the liquid phase flow field inside the flotation column.The flow characteristics of the gas-liquid two phases inside the cylinder are as follows:the spiral gas rises after the gas phase enters the cylinder.Within the measurement range,the greater the circulating flow rate,the lower the height and the greater the axial,radial and tangential speeds of the gas phase.In the radial direction,both the gas phase and the liquid phase are centrifugal,and the velocity at the axis is the largest,after which the radial velocity is slowly reduced until the velocity at the wall is close to zero.The tangential velocity of the gas phase and the liquid rotate in the same direction,approaching zero at the axial center,rapidly increasing along the radial direction,reaching a maximum value and then slowly descending to the wall surface.A CFD numerical model for accurately calculating the gas-liquid two-phase flow of a multi-fluid flotation column was established,including the Eulerian two-phase flow model,the RSM turbulence model and the tomiyama drag model.By comparing with the PIV gas-liquid two-phase flow measurement data,the results show that the tomiyama drag model has the best predictive ability for the gas-liquid two-phase flow field in the small multi-fluid flotation column,especially in predicting the axial velocity of the bubble.The deviation is 12.277%,which is 18%lower than the original model.Using the established two-phase flow numerical model,the numerical simulation of the internal flow field of the small multi-fluid flotation column under different working conditions is completed,and the comprehensive flow field information is obtained.The results show that the two-phase flow field inside the small multi-fluid flotation column has the following characteristics.The clean water flows from the tangential inlet at the inverted cone into the flotation column and spirals up along the wall surface,and reaches the gas-water interface at the top of the flotation column,and then spirals downward.Then it passes through the inverted cone and continues to rotate downwards to the middle port next to the wall of the lower column.A part of the water flows out from the mine outlet,and another part of the water spirals up along the axis of the flotation column under the action of the flower baffle,passing through the inverted cone section and finally reaching the gas-water interface at the top of the flotation column.As for the bubbles,they tangentially enter from the inverted cone,and under the action of the gravity field and the swirling force to the heart field,they gather toward the center and rotate up to the top of the flotation column to leave the flotation column at the gas-water interface. |
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