| dc.description.abstract | The wall effect is known to present difficulties when attempting to predict the pressure drop over randomly packed beds. The Nuclear Safety Standard Commission, “Kerntechnischer Auss-chuss" (KTA), made considerable efforts to develop an equation which predicts the pressure
drop over cylindrical randomly packed beds consisting of mono-sized spheres. The KTA was
able to estimate a limiting line, which defines the region for which the wall effect is negligible,
however the theoretical basis for this line is unclear. The goal of this investigation was to
determine the validity of the KTA limiting line, using an explicit approach.
Packed beds were generated using Discrete Element Modelling (DEM), and the flow through
the beds simulated using Computational Fluid Dynamics (CFD). STAR-CCM+R was used for
both DEM and CFD operations, and the methods developed for this explicit approach were
validated with empirical data. The KTA correlation predictions for friction factors were com-
pared with the CFD results, as well as the predictions from a few other correlations.
The KTA correlation predictions for friction factors did not correspond well with the CFD
results at low aspect ratios and low modified Reynolds numbers, due to the influence of the
wall effect. The KTA limiting line was found to be valid, but not exact. A new limiting line for
the KTA correlation was suggested, however the new limiting line improved little on the existing
line and was the result of some major assumptions. In order to improve the determination of
the position of the KTA limiting line further, criteria need to be established which determine
how small the error in predicted friction factor must be before the KTA correlation can be
accepted as accurate. | en_US |
