CFD-DEM Numerical Simulation Of Sludge Filtration In A High Density Sedimentation Tank

At present,CFD has been applied in many engineering fields and become a reliable technical means to solve various fluid flow problems.With the improvement of the CFD and the deepening of the research,the research provides a new technical way in water treatment field,including the principle of water treatment and related equipment,based on high density settling basin precipitation area as the research object,through the CFD-DEM coupling simulation,sludge floc particle capture particle capture the relationship between research,and then puts forward the more optimized scheme,and optimization of reactor,improve the effect of solid-liquid separation.In the second chapter,the discrete element method is used to simulate the filtration law of large particle bed with single particle filtration,which lays the foundation for the simulation of chapter three and chapter four.Through the use of EDEM software,the discrete simulation results show that the particle size ratio of small to large particles has a simple relationship with the trapping effect,and the critical particle size ratio for a single particle to pass through the bed of large particles is about 6.7.Change the size ratio,coefficient of friction and elastic recovery,to simulate the parameters by analyzing the critical particle size ratio,residence time,the radial diffusion and particle trajectory,the results show that the friction and elastic recovery coefficient will affect the critical particle size of particles through porous media bed than,also have certain influence to penetration probability,and change the elastic recovery coefficient to change the influence of friction is bigger.These relationships can potentially be used to describe the mechanism of particle capture in the filtration process.The third chapter is based on the second chapter to join,to simulate the fluid on the basis of simulation by CFD-DEM coupling simulation of the single particles into the porous medium fluid after filtering bed,change the parameters such as coefficient of friction,particle size ratio,the elastic recovery,through the analysis of the average number of collisions of particles and the average residence time,get the rule of the particle filter,Compared with the simulation results without fluid filtration,the average number of particle collisions and the average residence time in the presence of fluid are more than that in the absence of fluid without considering the change of elastic recovery coefficient.When the elastic recovery coefficient is changed,the number of particle collisions does not affect the residence time of particles,but the factor of fluid has an influence on it.Based on the simulation results of Chapter 2 and Chapter 3,the fourth chapter conducts CFD-DEM fluid-structure coupling simulation.With the help of Ligghts and Open FOAM software,the coupling simulation is carried out to change the conditions such as the flow rate and concentration of flocs from the Angle closer to the high-density sedimentation tank and explore the mechanism of capturing pollutant particles.Further provides the theoretical basis for optimizing the reactor.