CFD-DEM Simulation Of Spouted Bed Based On A Dynamic Two-grid Method

Spouted bed is widely used in energy,metallurgy,agriculture,drying and other fields because of its special flow and excellent structure.It is of great significance to fully understand the characteristics of the movement,mixing and heat transfer of particles in spouted bed for the optimal design of the reactor.In this paper,the computational fluid dynamics and discrete element method are combined,and Fortran language is used as the carrier for self-programming simulation,in which the gas-solid two-phase grid model is innovatively developed,and the dynamic two-grid model is used to analyze the flow mixing characteristics,heat transfer and heat storage characteristics of particles in the spouted bed.In this paper,the correctness and accuracy of the dynamic two-grid method are verified firstly.Compared with the expansion bed height obtained by the single-grid method,the particle-grid method and the dynamic two-grid method,the expansion bed height obtained by the experiment is more consistent with the simulation results of the dynamic two-grid method.At the same time,the experimental results and the particle volume fraction of the dynamic two-grid method also have a similar change trend.In the study of the flow and mixing characteristics of particles in the flat spouted bed,it is simulated that when particles in the bed move upward under the action of jet flow,the particle velocity is kept in a lower range.When the inlet velocity of the spout increases,the average particle volume fraction in the bed decreases,and the dramatic change of the flow field in the bed will accelerate the mixing process;when the number of spouts increases,the air in the spout area The speed of the body increases rapidly,the particles on both sides have a faster speed in the upward process,which makes the particles mix more effectively,and the rising rate of the mixing index is faster.In the simulation study of the heat transfer characteristics in the spouted bed,the initial position of the particles will have a certain impact on the temperature rise speed of the tracer particles,but after the tracking of the particle position,it can be inferred that the residence time of particles in the central jet area will be the main reason for the difference of the particle temperature;under the action of high-speed jet in spouted bed,strong convection heat transfer will make the particle temperature in the bed rapid With the increase of temperature,the heat conduction and radiation heat transfer only bring weak heat transfer effect.In terms of thermal storage characteristics,the number of nozzles,intake temperature,intake velocity,particle density and phase change will affect the thermal storage and efficiency of spouted bed.The more the number of nozzles,the faster the temperature change of particles,the higher the heat storage(release)and the thermal efficiency;the air inlet temperature has an obvious effect on the temperature change of particle layer,and reasonable control of the air inlet temperature can effectively improve the temperature rise rate of particle layer;the increase of air inlet speed makes the average temperature of particle layer increase linearly;the smaller the density,the faster the temperature rise rate of particles,and the denser the particles The thermal efficiency of the whole device is almost not affected by the particle density because of the slow temperature rise but the larger heat storage(release)under the same heat exchange time.Under the condition of relatively poor convective heat transfer intensity,phase-change particles have better thermal storage(release)effect than non phase-change particles,and the thermal storage and release efficiency is not significantly affected by the properties of particles.