X-ray particle tracking

X-ray-based imaging measurements of liquid foam flows

Person in charge:                     Dipl.-Ing. Tobias Lappan

Project leader:                         Dr.-Ing. Sascha Heitkam

Duration:                                  05/2020 – 04/2023

Funding:                                    DFG / Emmy-Noether

Project description

Optical observation is the only measurement technique commonly used for measuring liquid foam flows. Because liquid foams – especially wet foams with relatively high liquid fraction – are opaque for visible light, optical measurements are limited to the foam’s free surface or the bubble-scale foam structure close to a transparent wall. Using X-ray light instead of visible light, we are able to gain direct insight into foam flow phenomena that are usually hidden below the surface-near bubble layers.

© Tobias Lappan

Fig.: Metallic tracer particles act as tools for imaging measurements in liquid foam flows. While the foam is transparent for X-rays, the tracers are visualised detailed in X-ray images. Tracking algorithms are applied to measure the tracers’ motions, thus revealing the streamlines of the foam flow.

For this purpose, we employ custom-tailored particles made by means of 3D-printing as foam flow tracer particles. These tracers are supposed to attach to the bubble-scale foam structure, have been shown to follow the foam flow sufficiently well, and are clearly visible in time-resolved X-ray image sequences. Using tracking algorithms, the tracers’ translational and rotational motions are analysed in order to reveal the velocity field of the foam flow as well as bubble rearrangements in the foam structure.

Unlike quasi-two-dimensional optical measurements, this approach of X-ray particle tracking velocimetry (X-PTV) is applicable to liquid foam flows in three-dimensional flow configurations. To demonstrate the applicability and to test various foam tracer particles, we have measured liquid foam flows of different velocities and bubble sizes inside a curved flow channel, showing the expected rigid-body-like flow pattern in this configuration.

Publications

• T. Lappan, D. Herting, E. Zamaraeva, J. Stenzel, M. Ziauddin, A. Skrypnik, N. Shevchenko, S. Eckert, K. Eckert, S. Heitkam. Kombinierte optische und Röntgen-Messungen einer überlaufenden Schaumströmung. Accepted for an oral presentation at the 29. Fachtagung "Experimentelle Strömungsmechanik”, Ilmenau/Germany, September 2022.

• T. Lappan, D. Herting, E. Zamaraeva, J. Stenzel, M. Ziauddin, A. Skrypnik, N. Shevchenko, S. Eckert, K. Eckert, S. Heitkam. Kombinierte optische und Röntgen-Messungen einer überlaufenden Schaumströmung. Accepted for an oral presentation at the EUFoam 2022 conference, Krakow/Poland, July 2022.

• T. Lappan, A. Franz, H. Schwab, U. Kühn, S. Eckert, K. Eckert, and S. Heitkam. X-ray particle tracking velocimetry in liquid foam flow. Soft Matter 16(8):2093-2103, 2020. DOI: 10.1039/C9SM02140J
• T. Lappan. X-ray and neutron radiography of optically opaque fluid flows: experiments with particle-laden liquid metals and liquid foams. Dissertation, Technische Universität Dresden, 2021.