The same trend in hold-up was obtained for 15 kg/h at 495 RPM (Fig. 9B). In this case, the hold-up decreased substantially with increasing rotation rate (expected) for all blade configurations except for blade configuration #5. In this case, the rotation rate had a minor effect on the hold-up. This further suggests the possibility of larger stagnant regions created by a less effective convective mechanism for this blade configuration even at higher rotational speeds. For 45 kg/h at 112 RPM (Fig. 9C) and 495 RPM (Fig. 9D), the effect of the blade configuration was the same but the differences in hold-up values between blade configurations were substantially smaller. At 45 kg/h, a strong interaction between the flow rate and the impeller rotational speed was observed causing the hold-up for all blade configurations to be similar to each other. This can be an indication that powder convection is stronger due to the bulk flow while the effect of blade configuration is less significant at higher flow rates. A summary of the ANOVA (Table 6) shows that the flow rate and rotation rates have larger effects on the hold-up than the blade configurations with F-values of 18.63, 57.49, and 7.33, respectively.