4. Comparison with experimental results
Tracking each particle in a DEM simulation enables collection of
information to measure the performance of a screw conveyor, for
example: average speed of the particles, average mass flow rates,
power draw and energy dissipation. Fig. 9 shows mass flow rates,
obtained from these DEM simulations and from the experimental
measurements of Roberts and Willis [10], plotted against rotational
speed for various inclinations of the screw conveyor. Fig. 9 also shows
the theoretical maximum mass throughput of the screw conveyor
which is a linear function of the rotational speed of the screw. There is
excellent agreement between DEM predictions and the experimentally
measured throughput for the horizontal (0°) and the vertical
screw conveyor (90°) cases across the full range of screw rotation
speeds. The DEM predictions for the screw conveyor inclined at 30°
and 60° follow the correct qualitative trend but modestly underestimate
the mass flow rates by 16% and 24% respectively. These
underestimations may result from differences between particle–wall
and particle–particle friction which were not explored in this work
and/or particle shape effects. Cleary [7] has previously found that the
drawdown pattern in a screw conveyor hopper can be quite sensitive
to the particle shape, so this is likely to be a contributing factor. Thisweak change in the particle speed. The three curves are very close
showing that the average particle speed is almost independent of the
fill level. The maximum difference occurs for the 30% when the screw
is vertical with speed that is 11% higher than for the 70% fill level.