Liquid foam plays an important role in our daily life and industrial processes, such as flotation. Nevertheless, it is only sparsely investigated because of the reasons: Firstly, foam flow is a complex interaction of many mechanisms at different scales. Secondly, most flow measurement techniques are not applicable to foam, so measurement technique is lacking.
- Investigation of flow patterns,
- Development of benchmarks for foam flow
- Investigation of the Convective Instability
- Development of measurement methods for foam flow
- Fully transparent, vertical channel with 3x10cm cross section and 140 cm length
- Variable insets (cylinder, step, mesh)
- Forced drainage setup
- Bubble size 0.5 … 5 mm
- Optical observation of flow patterns
- Conductivity measurement with array of 8 electrodes
- Neutron imaging
The foam flow pattern for several insets has been measured, yielding interesting ideas for improving the froth flow in flotation columns. Also some patterns (cylinder, backward-facing step) might be useful benchmarks for numerical simulations.
The critical liquid fraction for the onset of the convective instability has been found to be smaller than literature suggests. However, at small liquid fractions the convective role stays in the lower part and does not fill the complete channel. This means, the process leading to the convective instability accumulates over channel height.
The Ultrasound-Doppler-velocimetry has been successfully applied to foam flow. Thus, UDV is the first velocity measurement technique for 3D foam flow with reasonable temporal and spatial resolution (2.5 fps, 2 cm) and reasonable uncertainty (15%).
Neutron Imaging has been found suitable to measure the liquid distribution in foam. This allows for drainage and dilatancy studies.
S. Heitkam, M. Rudolph, T. Lappan, M. Sarma , S. Eckert , P. Trtik , E. Lehmann, P. Vontobel, K. Eckert. Neutron imaging of froth structure and particle motion. Minerals Engineering (submitted)
R. Nauber, L. Büttner, K. Eckert, J. Fröhlich, J. Czarske, S. Heitkam. Ultrasonic measurements of the bulk flow field in foams. Physical Review E (submitted)