Numerical study of mixing pebble flow with different density in circulating packed bed

Based on the discrete element method, this work simulates the mixing flow of particles with different density in packed bed. The aim of this work is to explore the effect of density difference on the spatial distribution and flow characteristics of particles. After a premixed stacking, the particles start to discharge at fixed number rates being extracted from the bottom and then reinserted into the top of the bed to maintain the circulating flow. The results reveal that although different density can affect the local equivalent density, it has little influence on the uniformity and compactness of the whole bed with overall average voidage of about 0.39. The wall effects on particle distribution and voidage are observed near the wall. In addition, during the unloading time (time after the start of discharge), the proportion of light particles near the wall is always higher than 0.5 and keeps increasing. The increasing proportion and much higher number fraction of light particles compared with heavy one indicate that the heavy particles have the tendency to push the light particles to the side during the circulation process. Besides, the higher the ratio is, the more obvious this phenomenon is. Last but not least, both the axial and radial velocity profiles are analyzed, which show different patterns between the bottom and upper part of the packed bed.