XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 2801
the piezoelectric sensor is a promising tool for quantifying
turbulence in multiphase flows.
The piezoelectric vibration sensor’s spatial scale is 1cm,
meaning only turbulence above this size can be measured.
The sensor’s frequency response can reach 109 Hz, which is
sufficient to analyze any turbulent flow.
Electrical Resistance Tomography (ERT)
ERT was first accepted in the 1920s as a geophysical tech-
nique for detecting underground structures. Currents were
applied to one pair of electrodes and voltage responses were
measured at all others to acquire an image of the under-
ground structure, making it possible to get a more accurate
profile of, for instance, oil shales (Dickin &Wang, 1996).
This technique was further refined by Dines and Lytle
(Dines &Lytle, 1979 Lytle &Dines, 1980), who com-
bined conventional electrical probing measurement with
the more recent tomographic process. ERT has been suc-
cessfully applied to measure solid/liquid and gas/liquid mix-
ing in hydrocyclones, flotation columns, packed columns,
liquid-liquid extraction processes, precipitation processes,
and hydraulic conveying. Figure 10 shows a schematic of
the ERT with a 16-electrode ring. The differential voltage
ΔVϴ(ϕ) is produced by the current-driving electrode pairs
at θ and (θ+α). When air bubbles in flotation cells move
through the ERT measurement plane, the conductivity dis-
tribution fluctuates with turbulence. By measuring these
fluctuations, turbulence information can be extracted (Xie
et al., 2016).
Our team, Meng et al. (2014b and 2015a), fabricated
an intrusive ERT probe sized approximately 4cm in diam-
eter and used the probe in a 60L flotation cell with air and
water. The cell was operated at different air flow rates and
impeller speeds while measuring the voltage fluctuation. The
voltage measurement data was analyzed with a Green-Kubo
method, in which the velocity fluctuation was correlated
with the electrical flux through the transport coefficient.
The measured results were compared with kinetic energy
fluctuation measurements obtained using the piezoelectric
vibration sensor, the results when the air rate was 80L/min
are depicted in Figure 11. There is a squared correlation
between the ERT and the piezoelectric sensor’s results,
which validates that the ERT-derived quantity is a measure
of velocity fluctuation.
Our team tested ERT’s ability to measure turbulence in
multiphase flows in a Metso 3 m3 industrial flotation cell,
as shown in Figure 12. Measurements were made under dif-
ferent air flow rates, impeller speeds, and cell levels. The
shape of the turbulence distribution changed in a consis-
tent manner with cell hydrodynamic conditions in all of
the tests. The turbulence profiles measured by ERT have
the general shape expected in the system, i.e., turbulence
is low in the upper regions of the cell and increases sig-
nificantly in the impeller stator region. As impeller speed
increased, the size of the high-turbulence zone increased.
This indicates that ERT is capable of distinguishing differ-
ent turbulence intensities.
Figure 10. Schematic of the ERT with a 16 electrodes ring
Figure 11. Velocity fluctuation measured by ERT at an air rate of 80L/min compared with PVS results
the piezoelectric sensor is a promising tool for quantifying
turbulence in multiphase flows.
The piezoelectric vibration sensor’s spatial scale is 1cm,
meaning only turbulence above this size can be measured.
The sensor’s frequency response can reach 109 Hz, which is
sufficient to analyze any turbulent flow.
Electrical Resistance Tomography (ERT)
ERT was first accepted in the 1920s as a geophysical tech-
nique for detecting underground structures. Currents were
applied to one pair of electrodes and voltage responses were
measured at all others to acquire an image of the under-
ground structure, making it possible to get a more accurate
profile of, for instance, oil shales (Dickin &Wang, 1996).
This technique was further refined by Dines and Lytle
(Dines &Lytle, 1979 Lytle &Dines, 1980), who com-
bined conventional electrical probing measurement with
the more recent tomographic process. ERT has been suc-
cessfully applied to measure solid/liquid and gas/liquid mix-
ing in hydrocyclones, flotation columns, packed columns,
liquid-liquid extraction processes, precipitation processes,
and hydraulic conveying. Figure 10 shows a schematic of
the ERT with a 16-electrode ring. The differential voltage
ΔVϴ(ϕ) is produced by the current-driving electrode pairs
at θ and (θ+α). When air bubbles in flotation cells move
through the ERT measurement plane, the conductivity dis-
tribution fluctuates with turbulence. By measuring these
fluctuations, turbulence information can be extracted (Xie
et al., 2016).
Our team, Meng et al. (2014b and 2015a), fabricated
an intrusive ERT probe sized approximately 4cm in diam-
eter and used the probe in a 60L flotation cell with air and
water. The cell was operated at different air flow rates and
impeller speeds while measuring the voltage fluctuation. The
voltage measurement data was analyzed with a Green-Kubo
method, in which the velocity fluctuation was correlated
with the electrical flux through the transport coefficient.
The measured results were compared with kinetic energy
fluctuation measurements obtained using the piezoelectric
vibration sensor, the results when the air rate was 80L/min
are depicted in Figure 11. There is a squared correlation
between the ERT and the piezoelectric sensor’s results,
which validates that the ERT-derived quantity is a measure
of velocity fluctuation.
Our team tested ERT’s ability to measure turbulence in
multiphase flows in a Metso 3 m3 industrial flotation cell,
as shown in Figure 12. Measurements were made under dif-
ferent air flow rates, impeller speeds, and cell levels. The
shape of the turbulence distribution changed in a consis-
tent manner with cell hydrodynamic conditions in all of
the tests. The turbulence profiles measured by ERT have
the general shape expected in the system, i.e., turbulence
is low in the upper regions of the cell and increases sig-
nificantly in the impeller stator region. As impeller speed
increased, the size of the high-turbulence zone increased.
This indicates that ERT is capable of distinguishing differ-
ent turbulence intensities.
Figure 10. Schematic of the ERT with a 16 electrodes ring
Figure 11. Velocity fluctuation measured by ERT at an air rate of 80L/min compared with PVS results