| Venturi bubble generator is an important component of industrial flotation column with simple structure,high safety and low resistance energy.In the flotation process,the bubbles generated by venturi tubes can adhere the target mineral and transfer them to the surface of the liquid phase with the assistance of multiphase flow field and reagents,thus achieving the separation among various minerals.The structure of venturi tube directly determines its service life,operating cost,and the size and distribution of bubbles in the flotation column,significantly affecting the efficiency and economic benefit of ore dressing.Therefore,this work has conducted the simulation study of flow field characteristics and bubble behavior in venturi tube to guide the optimization of bubble generator structural parameters,which is of great practical significance for realizing economic and efficient mineral separation.In this work,SOLIDWORKS software is used to establish a simplified 3D model of venturi bubble generator.Then,based on the computational fluid dynamics,the simplified model is partitioned with appropriate precision mesh division,and furtherly two-phase flow model and RNG k-? model are used to conduct the numerical simulation on characteristics of fluid velocity and pressure and behaviors of bubble fragmentation and coalescence in the venturi tube.The main research results of this thesis are as follows:(1)The flow field characteristics in bubble generator in flotation system were studied.The velocity cloud diagram shows that the liquid flows steady-state when entering the pipe at an initial velocity of 2m/s,and the velocity reaches the maximum value of 20m/s at the throat and pipe.The two-phase flow is mainly axial flow,and the radial velocity difference decreases gradually with the flow.The pressure cloud diagram shows that the expansion and contraction sections are the most important areas of pressure change,which will form a negative pressure environment at the throat and pipe,and meet the self-priming conditions.The core area of bubble fragmentation of this type of bubble generator is between 45 mm and 60 mm in axial direction.The degree of bubble fragmentation is closely related to pressure gradient and turbulent kinetic energy.(2)The effect of gas-liquid flow rate on bubble size distribution of venturi bubble generator was studied.With the increase of gas flow rate from 2.0×10-4 kg/s to 5.0×10-4 kg/s,the degree of bubble breakage is strengthened,and the proportion of small bubbles with particle size less than 0.5mm increases from 51% to 75%.When it was further increased to 8.0×10-4 kg/s,the number of large bubbles increased,while the proportion of small bubbles smaller than 0.5mm decreased to 35%.It was considered that the larger gas flow enhanced the coalescence effect of bubbles.With the increase of liquid flow,the degree of turbulence in the bubble generator is enhanced and the degree of bubble breakage is increased.The proportion of small bubbles less than 0.5mm increases from 40% to 75%.(3)Explore the influence of geometric parameters on bubble generator performance.With the increase of the expansion Angle,the pressure gradient and turbulence intensity in the expansion section gradually increase,the turbulence degree in the tube gradually increases,and the pressure at the entrance also increases.The change of shrinkage Angle does not change the pressure gradient distribution in the fragmentation core region,and the bubble size decreases with the increase of shrinkage Angle.The pressure gradient and turbulent kinetic energy in the fragmentation core decrease with the increase of the throat diameter,and the bubble size increases with the increase of the pipe diameter.When the expansion Angle of this type of bubble generator is 9° and the throat diameter is 2.8mm,the turbulent kinetic energy inside the bubble generator is the best,which is most conducive to gas-liquid mixing and bubble fragmentation;The larger the contraction Angle of venturi bubble generator is,the greater the degree of bubble breakage is.However,when selecting the contraction Angle,energy saving and actual working conditions should be considered comprehensively.(4)VOF model was used to simulate the crushing behavior of a single bubble in bubble generator.The results show that in the axial position,the fragmentation degree of the single bubble set at the inlet pipe is stronger than that of the single bubble injected from the inlet pipe.In the radial position,the fragmentation degree of single bubble of Patch from the inlet pipe near the wall is stronger than that of Patch at the axis position. |
