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Combining optical and X-ray measurements of an overflowing foam.

Lappan, T.; Herting, D.; Stenzel, J.; Ziauddin, M.; Shevchenko, N.; Eckert, S.; Eckert, K.; Heitkam, S.

Froth flow is of central importance for mineral processing by froth flotation. In industrial-scale
flotation plants, the recovery of solid mineral particles [Neethling, 2002] and liquid from the overflowing froth [Stevenson, 2003] is monitored by optical observation and, therefore, limited to the
froth’s free surface. This lab-scale experimental work investigates the flow behaviour of an aqueous foam at a horizontal overflow in combined optical and X-ray radiographic measurements.
Simultaneously, the foam’s liquid fraction was determined by measuring the electrical conductivity between electrode pairs. The optical measurements, performed both through a transparent wall
and at the free surface of the overflowing foam, captured light reflexions on the foam bubbles,
which were analysed by adapting particle image velocimetry algorithms. While the opacity of the
foam limits optical measurements to the surface-near bubbles, our approach of X-ray particle
tracking velocimetry (X-PTV) [Lappan, 2020] sheds light on the three-dimensional foam flow.
The customised tracer particles used in this work consisted of a 3D-printed tetrahedral polymer
structure with a total of four small metal beads at its corners. Owing to their shape and the lightweight material composite, the tracers adhered to the bubble-scale foam structure and were carried
by the foam. X-ray radiography visualises the motion paths of each tracer’s metal beads, representing the local streamlines of the foam flow. Further, the X-ray radiographs map the foam’s
liquid fraction distribution, thus extending the local measurement of the liquid fraction by means
of the electrode pairs. X-PTV reveals comparatively high flow velocities of the three-dimensional
foam flow, in particular near the overflow, whereas the optical measurements are subjected to wall
or surface effects, yielding lower flow velocities. However, X-PTV with customised foam flow
tracers comes to its limit in unstable foams at high liquid fraction and high flow velocity.

  • Lecture (Conference)
    EUFOAM, 03.-06.07.2022, Krakow, Poland

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Publ.-Id: 35551