656 Figure 6 – Main effects of baffling (0: Stator only, 1: Baffles only) and Jg on mean Θjs In contrast, Jg exhibits a significant main effect on Θjs. Increasing airflow injection led to greater interface oscillations. This behaviour can be attributed to the increase in Njs required at higher gas rates. The higher impeller speed raises power input and turbulence levels, which, in turn, amplify interface instability. Although air introduction produces some turbulence dampening (Chapman et al., 1983), this effect is outweighed by the turbulence generated from operating at higher impeller speeds. Consequently, increasing Jg resulted in higher Θjs. Figure 7 illustrates the effect of Jg on Θjs for the two baffle configurations: stator and baffles. As previously discussed, increasing Jg elevates both Njs and Pjs, and consequently Θjs. It might be therefore expected that the higher Njs and Pjs observed with the stator would also produce larger interface oscillations. However, the opposite occurs. The stator confines turbulence to the lower region of the cell, creating a more quiescent upper zone (Morrison, 2017; Mesa, 2020). As a result, interface oscillations are lower when operating with the stator compared to baffles. Figure 7 – Impact of Jg on mean Θjs for stator (0) and baffles (1) arrangements At low Jg values (0.0 to 0.5 cm/s), both baffling configurations exhibit similar interface oscillations, which helps explain why the main effect of baffling was not statistically significant. Under these low-aeration conditions, impeller speed and power draw remain relatively low, so the absence of interface protection when using baffles has a minor influence. At higher Jg values (0.5 to 1.5 cm/s), both impeller speed and power draw increase substantially, and the stabilizing effect of the stator on the interface becomes more relevant. Consequently, oscillations are markedly lower with the stator than with baffles at elevated airflow rates.
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