Effects of fixed wall and pebble size ratio on packing properties and contact force distribution in binary-sized pebble mixed beds at the maximum packing efficiency state

Abstract The binary-sized pebble mixed beds at the maximum packing efficiency state were numerical simulated by the DEM simulation to investigate the effect of fixed wall and pebble size ratios. The evolution of the distribution of packing fraction and porosity, radial distribution function and contact force were given and analyzed with emphasis on the effects of the fixed wall and pebble size ratio. The results showed that the fixed wall will result in a reduction of average packing fraction and an obvious wall effect in local porosity distribution. With the increase of the pebble size ratio, the volume fraction of the wall affected regions gradually decrease. The variation of the local packing fraction of the binary-sized pebble bed is mainly determined by the partial packing fraction of large pebbles and the partial packing fraction of small pebbles, respectively, in the regions close to the fixed wall. Furthermore, the fixed wall has little effect on the radial distribution function and contact force. However, the pebble size ratios have great influence on the radial distribution function and the contact force in binary-sized pebble bed at the maximum packing efficiency state. With the increase of the pebble size ratio, the radial distribution functions of the whole pebble beds are consistent with that of small pebbles, and approach to that of the mono-sized pebble bed. In addition, with the increase of the pebble size ratio, a higher contact force can be obtained in pebble beds.