At the 95% confidence level, the regression model indicates that baffling arrangement does not have a statistically significant main effect on coarse particle suspension. However, it is significant with 94.6% confidence and is also present in the interactive term which had a significance of 99% and was therefore retained in the model. Moreover, previous studies strongly suggest that replacing the stator with baffles can significantly modify suspension performance. The stator converts a substantial portion of impeller energy into turbulence, which is detrimental to particle suspension (Nagata, 1975; Fallenius, 1987). In contrast, baffles promote mean flow, enhancing solids suspension efficiency (Nguyen & Schulze, 2003; Paul et al., 2004; Mesa, 2020). Consequently, operation with baffles resulted in a lower Njs than with the stator (Figure 2). Figure 2 – Main effects of baffling (0: Stator only, 1: Baffles only) and Jg on mean Njs It can also be concluded from Figure 2 that superficial gas velocity (Jg) exhibited a strong influence on coarse particle suspension. This agrees with previous studies in both mechanical flotation cells and mixing tanks, which have shown that aeration affects solids suspension (Rewatkar et al., 1991; Kraume, 1992; Mavros, 1992; Van der Westhuizen, 2004; Zheng et al., 2005; Lima et al., 2009). Air introduction decreases power draw and dampens local turbulence (Arbiter et al., 1969; Chapman et al., 1983; Warmoeskerken et al., 1984), while also reducing impeller pumping capacity and fluid velocities (Brayant & Sadeghzadeh, 1979; Nienow, 1997; Nelson et al., 2009). These effects hinder particle suspension, leading to higher Njs values at increased Jg. The relationship is non-linear: Njs rises with Jg, but the rate of increase diminishes at higher gas velocities. Although increasing Jg consistently elevated Njs, the magnitude of this effect depended strongly on the baffling arrangement (Figure 3). Operation with a stator generates hydrodynamic conditions characterized by higher turbulence and lower mean flow, making particle suspension more difficult compared to baffles. As a result, the rotor suspension performance is more sensitive to increasing Jg. Conversely, when baffles are used, suspension is more easily achieved, and the system becomes less sensitive to aeration rate. Thus, the impact of Jg on Njs is smaller in the baffled configuration.
RkJQdWJsaXNoZXIy MTM0Mzk2