The Structure Optimization And Bubble Production Mechanism Study Of Annular Jet Suction Mixing Device

As a method to separate fine slime minerals,forth flotation is in the high position of mineral processing.Flotation equipment,which act as media in mineral process,can directly affect flotation result,therefore the development and application of the flotation equipment has always been the focus of forth flotation research.The present flotation equipment are mainly mechanical flotation machine,jet flotation machine and flotation column.However,air-drawing mechanism and stirring mechanism,which are the core components of flotation machine's air supply and slurry mixing process,have merits and demerits in the working process.Combining with these merits and demerits,this paper gives an annular jet suction mixing device that utilize annular submerged jet to draw air,and meanwhile drive impeller rolling,in order to reduce energy loss and meanwhile get enough air,reasonable bubble distribution system and impeller stirring velocity,then obtain a three-phase flow field that benefiting to mineral flotation.To achieve this goal,this paper focus on mechanism that generate bubble from the corporation of submerged nozzle and impeller.By combining advanced testing technique such as CFD numerical simulation,high speed camera,PIV,pressure sensor,torque sensor and comparative validation test,four categories of research have been applied on annular jet air-drawing,submerged jet,jet impinging and impeller rotation stirring,involving mechanism configuration optimization and bubble formatting process,the main study substances and conclusions are given below:1.Air-fluid phase flow is taken as media,and Fluent simulation combined with validated test is adopted to research energy dissipation and air-drawing characteristics of annular jet nozzle in the condition of submerged jetting.This paper analyzes three categories,namely flow field distribution,turbulence energy dissipation and vorticity variety,impacting on nozzle's air-drawing rate and air-fluid ratio.The result shows that low pipe diameter has high controllability to air-liquid ratio under different input flow pressure;high input flow pressure has high controllability to air-liquid ratio under different pipe diameter ratio,air-liquid ratio increment in long throat is less than that of short's,however,long throat's air-liquid ratio has bigger value.All these features mentioned above are related to differential pressure between jet flow pressure of different input flow and water pressure in tank,and input flow's sealing effect on nozzle in different pipe diameter ratio and different throat.2.Assisted by diffusion silicon pressure sensor test system,submerged jet flow's influence on impinge pressure is analyzed under conditions of with or without air-drawing and different air-fluid ratio.The result shows that due to the existence of bubble,pinnate jet flow has bigger impinged force comparing with submerged jet flow,and the gap gradually shrinks with air-fluid ratio increases.Meanwhile,reduction process of air-fluid phase pinnate jet flow velocity and impinged voltage are also analyzed,the result shows that in the condition of low input pressure,throat length and pipe diameter ratio,pinnate jet flow impinged voltage reduction process in axial direction appears to be liner,and follows power function varying law in higher working condition,however,it follows normal distribution law in water flow cross section's radial direction.Whether axial flow that follows power function variation law or radial flow that follows normal distribution law,both velocities have a mutational site that changing from slowly reduction to sudden change,hence it provides a basis to select impeller's length and width and the distance between nozzle and impeller.Meanwhile,it shows that,affected by float force,jet flow appears to deviate to liquid level when away from nozzle,this phenomenon slows down in higher input pressure,throat and pipe diameter ratio.Dynamical torque sensor test system is built to study different blade length-width ratio and its torque variation.Theory analysis is combined to select the optimal length-width ratio and optimal blade number and nozzle number by conducting velocity test of combined different nozzle number and blade number,this also provides a research method to select nozzle and blade.3.During three stages,namely submerged jet,jet impinge and rotation stirring,bubble size and its distribution is analyzed.The result reveals that,in the submerged stage,with the increasing of input flow pressure,bubble's Sauter diameter decreases gradually,in size distribution,the amount of middle size and large size bubbles decrease,while bubble size concentration ratio increases and diameter distribution is more even;however,with the improvement of pipe diameter and throat length,bubble's Sauter diameter decreases gradually,in size distribution,the amount of middle size bubble increases,while bubble diameter distribution range decreases.Comparing with submerged jet stage,jet impinge stage share the same change rule but lower bubble Sauter diameter and higher middle size content in the same working conditions.In rotation stirring stage,bubble Sauter diameter stays the same,however,it has larger middle size content than other two stages,this is mainly because of jet impinge stage and stirring stage have obvious cut effect to large size particles when comparing to submerged jet stage.Based on turbulent energy k and turbulent dissipation rate ? under different variation parameters impacting on bubble size and distribution,turbulent energy and turbulent dissipation rate are introduced as "media variable" to explain and regulate bubble formatting system.4.Comprehensive evaluation is conducted to bubble formatting system,and the test shows that foaming agent can envelope bubble surface,therefore reduce bubble surface tension and increase bubble system's steady,and decrease different variable parameter's controllable range on regulating bubble size.Three devices,namely annular jet suction mixing device,jet air-drawing device and rotation stirring device impacting on bubble size and distribution is analyzed,the result shows that annular jet suction mixing device has a better bubble size distribution than jet air-drawing device,and similar to rotation stirring device,while,this device can form smaller bubble than the other two devices.