Study On Particle Spouting Characteristics In Rectangular Spouted Bed Based On CFD-DEM Method

The rectangular microwave spouted bed studied in this paper is a microwave combined drying equipment based on the improvement of nonuniformity of microwave heating.Its improvement principle mainly uses the design of electromagnetic field uniform distribution of microwave cavity structure and the random movement of material in the microwave cavity.In view of the previous research results of the research group,for rectangular microwave spouted bed with single feed port,the distribution of electromagnetic field in spouted bed is uniform when the length of spouted bed is 427x427mm and the height of spouted bed is 1000mm.In this paper,Computational Fluidized Dynamic coupled with Descrete Element Method coupling method is used to simulate the particle spouting characteristics in a rectangular spouted bed.Firstly,the mixing characteristics,single particle cycle time,particle velocity and bed pressure drop in the rectangular spouted bed were studied under three spouting velocities(us=ums,us=1.1ums,us=1.2u,ms,us is spouting velocities and ums is minimum spouting velocity).It is found that the mixing time of particles decreases with the increase of spouting velocity.When the velocity increases from us=ums to us=1.2ums,the cycle time is reduced from 5.4s to 2.2s.However,the circulation time of single particle is less affected by the spouting velocity.The velocity of the particles increases with the increase of the spouting velocity,and is symmetrically distributed in the central axis of the rectangular spouted bed.The bed pressure drop increases with the increase of spouting velocity.With the increase of bed height,the bed pressure drop gradually tends to a constant value.Secondly,the cycle time of single particle in a rectangular spouted bed was compared with that of a conventional conical-cylindric spouted bed at four different positions(z=40,80,120,170mm).The results show that the average circulation time of a single particle in the rectangular spouted bed is 1.925s at us=1.1ums,and the average circulation time of a single particle in the conical-cylindric spouted bed is 1.725s.The mixing characteristics of particles in the rectangular spouted bed at two different positions(z=120,369mm)were compared with that of a conventional conical-cylindric spouted bed.The results show that the mixing time of particles in the rectangular spouted bed and conical-cylindric spouted bed are both 2.8s.In this paper,100 particles were selected at the bottom of the spouted bed and the wall near the center.The changes of position with time was studied.It was concluded that the randomness of particle motion at the edge of the rectangular spouted bed was relatively poor.As a whole,the randomness of particle motion in a rectangular spouted bed is not better than that in a conical-cylindric spouted bed for particles at the special position.Finally,the axial velocity of particles and bed pressure at three different positions(z=369,569,769mm)of rectangular spouted bed and conical-cylindric spouted bed were compared in this paper.And the changes of pressure drop was compared between the rectangular spouted bed and conical-cylindric spouted bed with the spouting velocity when us=1.1ums.The results show that the axial velocity of particles and bed pressure are in good agreement with the variation of spouting velocity and bed height.