Reproducibility of Bo depends on the reproducibility of the magnesium bed. Thus, the results also show that similarity of beds is difficult to obtain. For the fine turnings the formation of voids or preferred flow channels in an otherwise dense bed will have a stronger impact on the obtained results than in a bed of coarse turnings, where more or bigger voids (higher void fraction) do already exist. The standard deviations demonstrate that for the description of a statistical, poured packed-bed no conclusions can be drawn from individual or single measurements. Therefore, to make a statement about residence time distributions in an average packed bed, multiple measurement runs must be performed. On an average, five measurement runs were investigated to calculate the mean Bodenstein number listed in table .