2796 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
can be achieved, which is sufficient to recover the frequency
content of many flows.
An LDA device (Morud and Hjertager, 1996) was
used to measure mean and turbulent gas bubble velocities
in a stirred vessel. The turbulent gas velocity in the radial,
axial, and tangential directions was measured at various
heights, gas flow rates, and impeller speeds. The accuracy
of the measurements was claimed to be within 1% of the
actual value. The single liquid phase LDA measurement
in Outokumpu’s flotation cell has been used to validate a
CFD model (Tiitinen, et al., 2003). In another applica-
tion, Kysela et al. (2013) measured the root mean square
of the turbulent velocity 15 mm under the impeller, from
the impeller axis to the wall, in a stirred vessel and analyzed
the velocity power spectra. The RMS turbulent velocity
results were normalized to the impeller’s peripheral speed.
The velocity PSDs (power spectral densities) were obviously
dependent on the impeller speed, and it can be observed
that they follow the trend of the Kolmogorov 5/3 law fairly
well.
LDA has been improved substantially to allow higher
accuracy in turbulence quantification. However, since it is
an optical technique, its applications are mainly limited to
one—or two-phase flows. LDA cannot be used in three-
phase systems, including industrial flotation cells.
Particle Image Velocimetry (PIV)
Particle Image Velocimetry (PIV) is an optical technique
often used for flow visualization and characterization.
Similar to LDA, it is a non-intrusive optical approach,
which utilizes seeding particles to measure the velocity
amplitude, and direction across a 2D measurement plane as
shown schematically in Figure 2. PIV requires the identifi-
cation of individual particles in a single image but does not
require the particles to be tracked between images. This can
be achieved with a medium concentration of seeding par-
ticles. When the seeding concentration is sufficiently low
that individual tracking of particles is possible, the method
is referred to as Particle Tracking Velocimetry.
Baldi et al. (2002) employed a PIV system compris-
ing a PCO Sensicam SVGA camera with Nikon 55 mm
lenses and a 3WArgon laser generating a light sheet with a
fiber optic and cylindrical lens fiber module (Figure 3). The
system was used to analyze the entire flow field in a stirred
vessel and small areas in the discharge stream region below
the impeller. The mean flow velocity and rms velocity were
measured and compared with LDA measurements found in
Fentiman et al. (1998), and showed good agreement with
LDA measurement data, proving the reliability of the PIV
system being used.
Brady et al. (2006) used a Digital Particle Image
Velocimeter (DPIV) with a CMOS digital camera and
Copper vapor pulsing laser. This setup can record the
velocity vectors of the fluid, the solid particles, and the air
bubbles in homogeneous isotropic turbulence generated
by cylindrical grids with great accuracy and kHz temporal
resolution.
PIV has been applied in a single-phase Wemco flota-
tion cell and shows good agreement with CFD modeling
(Kuang, et al., 2015). The PIV measurements and CFD
modeling revealed two strong vortices. One is below the
rotor level, and the other extends from the rotor region to
the free surface. They also showed a third small vortex near
the bottom of the disperser outside of the draft tube.
PIV is a powerful tool for quantifying turbulence in
fluid flows. It can image the velocity field at high temporal
and spatial resolution. However, the PIV technique can only
be used on transparent fluids seeded with solid particles.
Figure 3. Schematic of the PIV
can be achieved, which is sufficient to recover the frequency
content of many flows.
An LDA device (Morud and Hjertager, 1996) was
used to measure mean and turbulent gas bubble velocities
in a stirred vessel. The turbulent gas velocity in the radial,
axial, and tangential directions was measured at various
heights, gas flow rates, and impeller speeds. The accuracy
of the measurements was claimed to be within 1% of the
actual value. The single liquid phase LDA measurement
in Outokumpu’s flotation cell has been used to validate a
CFD model (Tiitinen, et al., 2003). In another applica-
tion, Kysela et al. (2013) measured the root mean square
of the turbulent velocity 15 mm under the impeller, from
the impeller axis to the wall, in a stirred vessel and analyzed
the velocity power spectra. The RMS turbulent velocity
results were normalized to the impeller’s peripheral speed.
The velocity PSDs (power spectral densities) were obviously
dependent on the impeller speed, and it can be observed
that they follow the trend of the Kolmogorov 5/3 law fairly
well.
LDA has been improved substantially to allow higher
accuracy in turbulence quantification. However, since it is
an optical technique, its applications are mainly limited to
one—or two-phase flows. LDA cannot be used in three-
phase systems, including industrial flotation cells.
Particle Image Velocimetry (PIV)
Particle Image Velocimetry (PIV) is an optical technique
often used for flow visualization and characterization.
Similar to LDA, it is a non-intrusive optical approach,
which utilizes seeding particles to measure the velocity
amplitude, and direction across a 2D measurement plane as
shown schematically in Figure 2. PIV requires the identifi-
cation of individual particles in a single image but does not
require the particles to be tracked between images. This can
be achieved with a medium concentration of seeding par-
ticles. When the seeding concentration is sufficiently low
that individual tracking of particles is possible, the method
is referred to as Particle Tracking Velocimetry.
Baldi et al. (2002) employed a PIV system compris-
ing a PCO Sensicam SVGA camera with Nikon 55 mm
lenses and a 3WArgon laser generating a light sheet with a
fiber optic and cylindrical lens fiber module (Figure 3). The
system was used to analyze the entire flow field in a stirred
vessel and small areas in the discharge stream region below
the impeller. The mean flow velocity and rms velocity were
measured and compared with LDA measurements found in
Fentiman et al. (1998), and showed good agreement with
LDA measurement data, proving the reliability of the PIV
system being used.
Brady et al. (2006) used a Digital Particle Image
Velocimeter (DPIV) with a CMOS digital camera and
Copper vapor pulsing laser. This setup can record the
velocity vectors of the fluid, the solid particles, and the air
bubbles in homogeneous isotropic turbulence generated
by cylindrical grids with great accuracy and kHz temporal
resolution.
PIV has been applied in a single-phase Wemco flota-
tion cell and shows good agreement with CFD modeling
(Kuang, et al., 2015). The PIV measurements and CFD
modeling revealed two strong vortices. One is below the
rotor level, and the other extends from the rotor region to
the free surface. They also showed a third small vortex near
the bottom of the disperser outside of the draft tube.
PIV is a powerful tool for quantifying turbulence in
fluid flows. It can image the velocity field at high temporal
and spatial resolution. However, the PIV technique can only
be used on transparent fluids seeded with solid particles.
Figure 3. Schematic of the PIV