Numerical Simulation Of Double-Nozzle Spouted Bed Based On Double-Grid

Spouted bed is widely used in energy,metallurgy,agriculture and drug drying industry because of its special flow characteristics and excellent structure.It is very important to fully understand the collision of particles in spouted bed for the design and optimization of reactor.The limitation of experimental methods that can not obtain micro-physical information of particles makes the numerical simulation method to study dense gas-solid two-phase flow system become the mainstream in academia..In this paper,computational fluid dynamics(CFD)and discrete element method(DEM)are combined.Fortran language is used as the carrier to program the algorithm.OpenMP parallel computation statement is added to improve the calculation speed of the program.Based on the existing flow program,the development and optimization of three-dimensional double grid heat transfer program are carried out.The gas-solid two-phase flow,heat transfer characteristics and heat storage capacity of the spouted bed are studied.The gas-solid two-phase flow characteristics and particle mixing characteristics of double-nozzle spouted bed are simulated.The simulation results show that the particle position,the distribution of particle and gas velocity,the distribution of particle volume fraction along the bed height,and the Lacey mixing index under various operating conditions change with time.The results show that the increase of the number of nozzles leads to a great increase in the mixing velocity of particles and a significant decrease of the "dead zone" of the bed.In a double-nozzle spouted bed system,the vertical average velocity of gas peaks at the axis of the two nozzles,while that of the particles only shows a wave near the axis of the center of the bed.With the increase of nozzle gas velocity,the average particle volume fraction of the bed decreases significantly,and the expansion height of the bed increases significantly.The influence of nozzle characteristics and particle properties on the overall mixing process is mainly reflected in the improvement of mixing speed.The heat transfer characteristics of double-nozzle spouted bed are simulated.The schematic diagrams reflecting the temperature change trend of particles and gases and the proportion of heat transfer mechanisms in the process of particle temperature change areobtained by simulation.The results show that in the start-up stage of heat storage and release,the temperature variation rate of the average temperature of the granular layer is faster,and the temperature rise and temperature drop curves change from steep to slow with the passage of time;the gas phase temperature field in the upper and lower parts of the bed presents opposite distribution law;the convective heat transfer between gas and solid dominates the process of the increase of the particle temperature.The effects of heat conduction and radiation heat transfer are both very weak,and the particle temperature rise rate is closely related to the position of the bed.The heat storage capacity of double-nozzle spouted bed is simulated.The schematic diagrams reflecting the heat storage efficiency of bed under various working conditions and the variation of heat storage and release with time are obtained by simulation.The results show that the thermal storage capacity of spouted bed mainly depends on the thermal storage capacity of granular layer;among many factors of nozzle characteristics,the number has the greatest influence on the thermal storage efficiency,and there exists an optimum inlet velocity,which making the thermal storage capacity of the bed the best;among many factors of particle properties,the size of density and friction coefficient has a great influence on heat storage efficiency.