2696 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
increasing superficial gas velocities. A similar trend is also
seen in Aubin et al. 207 (2004), who observed a decrease in
mean liquid velocities and TKE in the bulk of the tank due
to higher aeration. The 208 transition from homogeneous
to heterogeneous flow at high gas velocities, as observed by
Gezork et al. (2000) may 209 also contribute to a decrease
in TKE. Additionally, the presence of bubbles in gas-liquid
two-phase flows, as argued 210 by Hosokawa et al. (2012)
modifies the fluid flow, hence affecting the TKE.
Piezoelectric Force Measurements in Different Radial
and Axial Positions (35L)
The spatial distribution of the force signal in single-phase is
shown in Figure 4. The signal is higher near the rotor where
high shear rates and vortex shedding is expected, which
turns weaker as the distance from the bottom of the tank
increases.
The measurements were also done in two-phase at three
different air flow rates as shown in Figure 6. It is observed
that overall, the force signals in two-phase is higher than
that of flow without bubbles. This is shown in Figure 5
which shows the average force calculated over different Jg
values (0 to 1.1 cm/s). Especially, at higher gas rates, the
bubble-induced turbulence is expected to be higher. RANS
simulations by Colombo &Fairweather (2015) in bub-
bly and single-phase flows also showed higher TKE values
when comparing 1-phase to 2-phase.
Overall, and particularly in the case of R =9cm, a
significantly higher change of the average force signals
between H =8cm and H =16cm can be observed than
between H =16cm and H =25cm. This is also prominent
in the case of higher air flow rates. This is expected as tur-
bulence is concentrated in the rotor region and decays with
increasing distance from the rotor. The highest turbulence
kinetic energy dissipation rates were observed close to the
impeller blades and stator walls, where the radial jets strike
the walls periodically (Ducoste, 2002). The flow around the
rotating impeller blades interacting with stationary baffles
can cause rapid changes in flow characteristics, leading to
high levels of turbulence and higher shear rates (Lee &
Yianneskis, 1998). Moreover, Worth &Nickels (2011) also
observed that a strong correlation exists between regions
of intense rotation and energy dissipation, with intermit-
tent events clustered in the periphery of larger scale vor-
tices. These random intermittent events could explain a
certain disparity between the force signal occurs, that is,
Figure 4. PVS Force measurements in single-phase with varying tip speeds, at radial position: (a) 9cm (b) 15cm
Figure 5. PVS Force measurements in single-phase flow (Jg
=0cm/s) and with varying gas flows (Jg =0.8, 0.95, and
1.1 cm/s)
increasing superficial gas velocities. A similar trend is also
seen in Aubin et al. 207 (2004), who observed a decrease in
mean liquid velocities and TKE in the bulk of the tank due
to higher aeration. The 208 transition from homogeneous
to heterogeneous flow at high gas velocities, as observed by
Gezork et al. (2000) may 209 also contribute to a decrease
in TKE. Additionally, the presence of bubbles in gas-liquid
two-phase flows, as argued 210 by Hosokawa et al. (2012)
modifies the fluid flow, hence affecting the TKE.
Piezoelectric Force Measurements in Different Radial
and Axial Positions (35L)
The spatial distribution of the force signal in single-phase is
shown in Figure 4. The signal is higher near the rotor where
high shear rates and vortex shedding is expected, which
turns weaker as the distance from the bottom of the tank
increases.
The measurements were also done in two-phase at three
different air flow rates as shown in Figure 6. It is observed
that overall, the force signals in two-phase is higher than
that of flow without bubbles. This is shown in Figure 5
which shows the average force calculated over different Jg
values (0 to 1.1 cm/s). Especially, at higher gas rates, the
bubble-induced turbulence is expected to be higher. RANS
simulations by Colombo &Fairweather (2015) in bub-
bly and single-phase flows also showed higher TKE values
when comparing 1-phase to 2-phase.
Overall, and particularly in the case of R =9cm, a
significantly higher change of the average force signals
between H =8cm and H =16cm can be observed than
between H =16cm and H =25cm. This is also prominent
in the case of higher air flow rates. This is expected as tur-
bulence is concentrated in the rotor region and decays with
increasing distance from the rotor. The highest turbulence
kinetic energy dissipation rates were observed close to the
impeller blades and stator walls, where the radial jets strike
the walls periodically (Ducoste, 2002). The flow around the
rotating impeller blades interacting with stationary baffles
can cause rapid changes in flow characteristics, leading to
high levels of turbulence and higher shear rates (Lee &
Yianneskis, 1998). Moreover, Worth &Nickels (2011) also
observed that a strong correlation exists between regions
of intense rotation and energy dissipation, with intermit-
tent events clustered in the periphery of larger scale vor-
tices. These random intermittent events could explain a
certain disparity between the force signal occurs, that is,
Figure 4. PVS Force measurements in single-phase with varying tip speeds, at radial position: (a) 9cm (b) 15cm
Figure 5. PVS Force measurements in single-phase flow (Jg
=0cm/s) and with varying gas flows (Jg =0.8, 0.95, and
1.1 cm/s)