Numerical Simulation Of Particle Motion Law Under The Action Of Bubbles Based On CFD-VOF-DEM Model

In the air flotation process in the environmental field,in the flotation process in the mineral processing field,and in the coal gasification furnace quenching chamber in the coal gasification field,etc.There are three-phase flow processes of bubbles passing through solid-liquid two-phase process.There is a common scientific problem in this process,that is,the particles will undergo processes such as suspension,sedimentation and entrained under the action of bubbles.The particle motion under the action of bubbles affects efficiency of heat and mass transfer in the operation of industrial equipment and process to a certain extent.It can be seen that it is of great significance to study the movement of particles under the action of bubbles.The specificity of the three-phase flow process cannot be well reflected by experimental methods due to the complex interaction between phases.Moreover,it is difficult to carry out the experiment,which has certain limitations such as cost,cycle and measurement.Computational fluid dynamics(CFD)has been widely used because of its low cost and ability to simulate complex processes.Therefore,this thesis takes the process of bubble passing through solid-liquid two-phase as the research object.The motion of bubbles and particles in this three-phase flow process was studied by numerical simulation in order to understand the movement and distribution characteristics of particles in three-phase system.This has important guiding significance for promoting the improvement of process flow.The numerical simulation in this thesis was based on the Computational Fluid Dynamics(CFD)and Discrete Element Method(DEM).The gas-liquid phase was regarded as a continuous phase and the Volume of Method(VOF)was used to track the gas-liquid interface.The particles were regarded as a discrete phase.The CFD-VOF-DEM gas-liquid-solid three-phase flow numerical model and the corresponding numerical simulation platform were established.The process of bubble passing through the solid-liquid two-phase liquid pool was numerically simulated.Then the independence of the grid is verified.On this basis,the model established in this thesis was verified.The numerical simulation results in this thesis were compared with the experimental results and the simulation results in the literature,respectively.The comparison results were in good agreement,which proved the accuracy and rationality of the model built in this thesis.Firstly,the gas-liquid-solid three-phase motion process and its motion law under the action of single bubble and double bubbles were studied by using the mathematical model established above.Secondly,the influence of single / double bubbles on particle number distribution is compared and analyzed.The variation law of the movement distribution of10μm,50μm,100μm and 500μm particles in the liquid pool was obtained.The results showed that the upward velocity distribution will be formed at the lower end of the bubble during the rising process,which will entrain the particles.The leading bubble will carry and accelerate the trailing bubble during the rising process of double bubbles.The 10μm and 50μm particles were basically suspended in the liquid pool,the 100μm particles were in a slow sedimentation state,and the 500μm particles were in a rapid sedimentation state,and there was basically no particle entrainment phenomenon.The results showed that compared with single bubble,the interface between solid-liquid suspension and pure liquid decreased faster under the action of double bubbles.Double bubbles can entrain particles to a higher height and the numbers of particles were entrained is more.Finally,based on the study of the gas-liquid-solid three-phase motion process and its motion law under the action of single bubble and double bubbles,the gas-liquid-solid three-phase motion process and its motion law under the action of bubble clusters were studied in this thesis.The law of particle concentration distribution was obtained and the effects of different particle sizes,bubble diameter,pipe diameter and inlet gas velocity on particle entrainment law were analyzed.The results showed that under the bottom immersion mode,the smaller the particle size is,the higher the particle entrainment height is,and the more particles are entrained.The larger the inlet gas velocity is,and the stronger the disturbance effect of bubble group on solid-liquid suspension is.In the top immersion mode,the 10μm particles move upward against the pipe wall after entering the liquid pool,while the 500μm particles move directly to the bottom of the liquid pool after entering the liquid pool.The gas-solid separation in the process of gas-solid two-phase passing through the liquid pool can be divided into three processes: the impact process,the carrying process and the crushing process.