5.2.2. Effect of blade configuration on mean residence time
The effect of blade configuration on the MRT (t) for all experiments in this section are plotted in Fig.10. The MRT showed a clear trend, similar to the hold-up results as expected. In general, the MRT for blade configuration #5 was higher for all experimental conditions when compared to all the other blade configurations, as expected, followed by configurations #4 through #1, in that order. These differences in MRT caused by the blade configuration were statically significant (p-value = 0.022). For 45 kg/h, the MRT was lower and almost identical for all blade configurations, especially at 495 RPM. The recirculation and the convective mechanisms previously described also explain the effect of blade configuration on the MRT. As the rotation rate increases, the MRT results for the blade configurations become almost identical. At higher rotation rates, the rotational forces in the shaft overcome the influence of the blade configuration. This means that the convective mechanism governs mixing and the recirculation mechanism created by the alternating blade configurations no longer has a significant effect on the RTD. In previous work by Vanarase and Muzzio [8], comparison of two blade configurations showed opposite results. Their findings described that the MRT was similar at lower rotation rates and became substantially different at higher rotation rates for blade configurations with forward and alternate configurations. In their case, the MRT was also higher for an alternating blade configuration, which created more recirculation of the powder inside the continuous mixer. Nevertheless, the blade configurations studied as well as the L:D of the mixer were very different The summary of the ANOVA for MRT for the effect of blade configuration is shown in Table 6.