| The sand filter plays an important role in the separation and recovery of solid particles,gas purification,and environmental protection with the advantages of simple structure,affordable cost,low energy consumption,and convenient maintenance.The gas-solid two-phase flow inside the sand filter is an extremely complicated three-dimensional strong rotational flow,and the interaction between gas and solid is intense.At present,many scholars have done detailed research on the gas phase velocity field and pressure field of sand filter.However,the study of its internal particles movement characteristics and the identification of the sand volume are rarely involved.Therefore,it is a key issue that restricts the automated application and development of the sand filter.In view of the complicated flow system inside the sand filter,this paper adopts the current advanced gas-solid two-phase flow simulation method-CFD-DEM coupling method.This method uses the computational fluid dynamics software FLUENT to describe the flow and transfer behavior of the gas phase and simultaneously uses the particle mechanics software EDEM to describe the motion and collision behavior of the particle phase,and the two software are seamlessly coupled and calculated in parallel,this way also takes into account the coupling between gas and solid phases.Finally,the two-phase flow inside the sand filter was numerically simulated.Based on these works,the main research contents and conclusions of this paper are as follows.(1)Based on the working characteristics of the sand filter,its initial model was established.The Reynolds Stress Model(RSM)in FLUENT was applied to simulate the gas flow field inside the filter,and the velocity,pressure and turbulent distribution of the gas flow inside the filter were analyzed.(2)Using particle mechanics software EDEM to track the trajectory of individual particle,it was found that after undergoing centrifugation,the particles moved downward spirally along the wall and formed a spiral gray band on the wall.During the entire movement of the particles,the particles and the gas collide violently in the inlet section,and the momentum exchange between the two phases is frequent.Therefore,the particles receive the greatest coupling force in this area.(3)According to the working characteristics of the sand filter,the FLUENT-EDEM coupling method was used to simulate the gas-solid two-phase flow by taking respective advantages of the FLUENT and EDEM.The sedimentation process,the sedimentation velocity,the spatial distribution,the volume fraction and the number of the particles in the sand filter were analyzed.It was found that along the radius of the filter,the particle concentration in the trapping zone was the highest,in the separation zone was medium,and in the escape zone was the smallest.At the same time,the concentration of particles at the same cross section increased from the outside to the inside.(4)Analysis of the simulation results showed that the number and volume of particles in the sand tank increased linearly with time,and the volume of sand increased nonlinearly with the increase of pressure drop.Further discussion revealed that the pressure drop had a more pronounced relationship on the volume of sand.Then through the regression of the simulation results,the equation of pressure drop and sand volume of this sand filter was obtained and evaluated.In the end,the equation was verified by the equipment operation manual and achieved better results,therefore the optimization proposal was given.Through the above research,this paper has laid a certain theoretical foundation for further identifying the sand volume in the tank of sand filter,and provides a reference to achieve the automatic sand removal of sand filter in engineering practice. |
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