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This paper presents the cycling of a novel low-cost Na-Zn liquid metal battery. Its 600 °C operating temperature presents multiple challenges that must be overcome to achieve commercial viability, both from a structural and electrochemical perspective. To enable long-term cycling of the Na-Zn battery in a realistic environment, we have developed a reusable, hermetically sealed, high temperature and sufficiently corrosion resistant cell concept. The design as well as various approaches for assembling and filling the cell are presented. The factors considered when selecting specific components are documented and explained. The active volume of the cell design can be up to 40 ml, corresponding to a nominal capacity of 1 A h, while the entire cell body weighs around 800 g and costs approximately €200 ($215). The performance of the cell is demonstrated in terms of longevity (1000 h) and high discharge current density (100 mA cm-2). The manuscript not only presents the first long-term cycling performance of the novel Na-Zn chemistry achieving Coulombic efficiency of up to 80%, but also demonstrates the design's versatility with in situ dynamic neutron radiography of the cell.

Water electrolysis produces hydrogen and oxygen gas by splitting liquid water in an electrochemical reaction. The further development of electrolysers faces currently unexplored operating conditions, particularly by increasing the electric current density, affecting the gas formation and bubble transport in the porous transport layer. Since this gas-liquid two-phase flow is not accessible by optical techniques, we employ time-resolved X-ray and neutron radiography, aiming for imaging flow measurements of the gas transport by mapping the local gas fraction distribution over time. On a laboratory scale, we performed radiographic imaging of bubble flows through open-porous metal and polymer foams of different pore size and surface functionalisation. This conference contribution presents main conclusions of our experimental study and showcases the advantages but also limitations of X-ray or neutron radiography for investigating multiphase flows within optically opaque structures. We observed preferred motion paths of bubbles and found that especially small bubbles are significantly slowed down when flowing through the foam structures, even in the case of a hydrophilic surface character. In summary, we visualised the gas transport depending on the bubble size in relation to the foam pore size and the wettability of the inner foam surface, thus highlighting the potential of radiographic techniques.

In foam fractionation, to enhance the product yield, the seperation process can be intensified by the successive contraction and expansion of the aqeous foam. Performing optical bubble size measurements in combination with conductivity-based measurements of the surfactant concentration, Li et al. found that contracting the foam flow in a vertical column does neither affect the liquid flux nor the surfactant concentration, whereas a sudden expansion decreases the liquid flux. To gain comprehensive insights into the liquid fraction distribution and the velocity field of the foam while flowing through contracting or expanding geometries, we combined optical flow measurements, X-ray transmission imaging as well as X-ray particle tracking velocimetry (X-PTV) in a nozzle flow experiment as shown in Figure 1. This conference contribution presents the imaging techniques and reports experimental findings at different foam flow conditions. In the case of a diverging nozzle, we gradually increased the superficial gas velocity while keeping the bubble size constant, thus observing the transition from the expected plug flow to a detached flow including recirculation zones. In future experiments, the flow configuration investigated here will serve as a benchmark: performing parallel measurements with X-PTV, we aim to validate the approach of magnetic particle tracking (MPT) using planar Hall effect sensors.

Data and source code accompanying the publication Nash et al. (2024) Neutron imaging of high-temperature Na-Zn Cells: implications for cell design and fabrication. For the purposes of reproducing volume integration and self-discharge current calculations.

The data set includes original data for the paper "Neutron radiography of an anisotropic drainage flow".

The dataset contains python scripts to reproduce the Turner diagram (double diffusive convection), the image on voltage efficiency and the 1D temperature profile.

This paper presents the analysis of particle-laden liquid metal flow around a cylindrical obstacle at different obstacle Reynolds numbers. Particles in liquid metal are imaged using dynamic neutron radiography. We present the results of particle tracking velocimetry of the obstacle wake flow, and demonstrate the capabilities to assess both temporal and spatial characteristics of turbulent liquid metal flow, and validating the precision and accuracy of our methods against theoretical expectations, numerical simulations and experiments reported in literature. We obtain the expected linear vortex shedding frequency scaling with the obstacle Reynolds number and correctly identify the universal algebraic growth laws predicted and observed for trajectory curvature in isotropic homogeneous two-dimensional turbulence. To our knowledge, this is the first such result for liquid metals. Particle residence times within the obstacle wake and velocity statistics are also derived and found to be physically sound. Finally, we outline potential improvements to our methodology and plans for further research using neutron imaging of particle-laden flow.

Non-metallic inclusions in metallic materials are a key challenge in metallurgical processing such as steelmaking. Aiming to control the population of inclusions and to remove them from the metal in its molten state, gas bubbles are commonly used for melt stirring, homogenisation and purification during ladle treatment. However, the effects of bubble–inclusion interactions in molten metals are not yet well researched, as experimental investigations at high processing temperatures are challenging. To circumvent these harsh conditions, model experiments are performed at room temperature, employing low-melting alloys based on gallium. In such laboratory-scale experiments, the interactions between gas and solid phases in the liquid metal are observable by means of transmission imaging with X-rays or neutron radiation. Starting from the essentials of the measurement principle, this contribution presents two exam-ples of dynamic X-ray and neutron radiography studies in liquid metals, thus showcasing the unique capabilities as well as limitations of imaging measurements at high spatial and temporal resolution. X-ray radiography is able to image both, gas bubbles and solid particles in the liquid metal, at high contrast-to-noise ratio, but only if these particles are rather coarse and heavy [1]. Using neutron radiography, the focus is on a configuration motivated by a single bubble: the particle-laden liquid metal flow around a cylindrical obstacle, measured at 100 Hz imaging frame rate [2]. Combining particle image velocimetry and particle tracking algorithms, we detected particle trajectories in the cylinder wake flow [3], derived particle residence times and velocity statistics [4]. Such radiography studies provide valuable insights into multi-phase liquid metal flows, and the experimental findings may improve the understanding of the inclusion behaviour in bubble-stirred metallurgical reactors. References [1] Lappan T., Sarma M., Heitkam S. et al. Materials Processing F

In water electrolysis, the porous transport layer (PTL) is an essential component of both proton (PEM) as well as anion exchange membrane (AEM) electrolysers. Besides establishing an electrical contact, the PTL enables the electrolyte to be transported to the anode. In the opposite direction, the oxygen (O2) formed at the anode must be transported away, resulting in a complex counterflow of liquid and gas through the PTL, thus limiting the mass transport and, consequently, the conversion of electrical energy. The further development of electrolysers faces so far unexplored operating conditions, in particular by increasing the electric current density. This, in turn, affects the formation and transport of gas bubbles in the PTL, which is not yet sufficiently understood. As the gas-liquid two-phase flow in the PTL is inaccessible for flow measurement by optical methods, we employed time-resolved X-ray and neutron radiography. Using the model experiment sketched in Fig. 1, we aimed for imaging measurements of the gas transport through open-porous foam by mapping the gas fraction distribution over time. In previous experimental studies, we have used X-ray and neutron radiography for flow visualisation in optically opaque fluids such as liquid metal [1] and aqueous foam [2]. Similar to the approach of radiographic measurements of the liquid fraction in aqueous foam [3], this conference contribution showcases the detection and tracking of bubbles based on their gas fraction in X-ray or neutron images. As exemplarily illustrated in Fig. 2, we observed preferred paths of the bubbles moving upwards through the open-porous foam samples. Moreover, we found that bubbles smaller than the pore size are significantly slowed down, even in the case of a hydrophilic surface character of the foam. In summary, the measurement results and conclusions from our experimental parameter study are available for comparison with computational fluid dynamics.

The flow behaviour of liquid foam is of central importance in froth flotation for mineral processing. Flotation separates valuable mineral particles from gangue material based on the surface wettability. To this end, the solids are finely ground and suspended in an aqueous solution with flotation reagents. In aerated flotations cells, gas bubbles selectively attach to the hydrophobic mineral particles, rise to the surface, and form a froth. To recover the valuables, they are transported out of the flotation cell with the froth. In flotation plants, the recovery of solid and liquid is monitored by optical observation of the overflowing froth. However, this monitoring is limited to the free surface of the particle-laden froth. Aiming for detailed insights into the flow behaviour underneath the surface-near foam bubbles, the laboratory-scale experiment in this work investigates the velocity field of an overflowing foam in combined optical and X-ray measurements. For this purpose, foam was generated continuously, moved similar to a plug-flow in a vertical channel with rectangular cross-section, and flowed off over a one-sided horizontal weir into the open surrounding. The imaging measurements focused on the foam flow in the region of interest around the weir. Simultaneously, the liquid fraction of the foam was monitored by measuring its electric conductivity between electrode pairs mounted near the weir. We used aqueous foams of two different surfactant concentrations but similar bubble size range and superficial gas velocity, yielding around 10 % liquid fraction. The optical measurements carried out through the transparent side wall of the flow channel as well as at the free surface of the overflowing foam. They captured light reflections on the foam bubbles were analysed by an adapted particle image velocimetry algorithm. While the opacity of the foam limits optical measurements to the wall- or surface-near foam bubbles, our approach of X-ray particle tracking velocim

X-ray radiographic imaging is an efficient tool for investigating flow phenomena and solidification processes in optically opaque metallic alloys. This contribution is an overview of the latest advances in in-situ radiographic experiments made by the authors, as well as recent applications, including magnetohydrodynamic systems. We investigated a range of phenomena, such as bubble flow in liquid metal under an applied magnetic field, collective bubble dynamics, particle flow in liquid metal channels, and mesoscale solidification of alloys. Radiography measurements in liquid/solidified metal experiments are inevitably performed under adverse conditions of low signal-to-noise ratio, low image contrast, scattering, etc. To extract meaningful information from experimental data we combine both well-known methodology of data processing and our original codes. Examples of image analysis and results of in-situ experiments performed with low melting point alloys are presented and discussed in this contribution. A focus of these experiments is exploring scaled-down representative systems of industrial processes in metallic alloys.

The cost-efficient production of green hydrogen using renewable energies requires next-generation proton exchange membrane (PEM) electrolysers to be operated at higher current density. Under this new operating condition, the elevated temperature of the ultra-pure water and its supersaturation with oxygen on the anode side have strong effects on the formation and transport of gas bubbles. The resulting gas-liquid two-phase flow through the porous transport layer at the membrane electrode assembly is characterised by up to 50 % gas fraction, which is exceptionally high. Such a foam-like flow within the porous medium is not accessible by optical measurements. Instead, we performed imaging flow measurements by means of time-resolved radiography using polychromatic X-rays as well as thermal neutrons at 100 frames per second imaging frame rate. On a laboratory scale, we aimed to study the bubble transport by mapping the local gas fraction distribution over time. This conference contribution presents two model experiments with open-porous metal and polymer foams, namely made of nickel and polyurethane, showcasing the advantages but also limitations of X-ray and neutron radiography for investigating bubble transport phenomena within such foam structures. In both experiments, foam samples of approximately 70 mm x 70 mm in width and height were sandwiched between the X-ray- or neutron-transparent front and back windows of a vessel filled with deionised water. As neutrons are strongly attenuated in water, the thickness of the water-filled vessel and the foam sample were set to 5 mm along the beam direction in all measurements. Bubbles were generated continuously by injecting compressed air at different but constant volumetric flow rates through a single hollow needle releasing the bubbles directly into the water-soaked foam. Based on calibration radiographs acquired both in the absence and presence of water, quantitative image analysis yielded a pixelwise mapping of the gas fr

Froth flotation, widely used in the processing and recycling of ores and raw materials, employs hydrophobic interactions between bubbles and particles to concentrate valuable materials in an overflowing froth phase. The flotation process, and therefore the quality of separation, is affected by the height of the 3-phase foam, called froth, and thus by the foamability. Within a joint European industry doctorate program between the Institute of Fluid Dynamics, HIF and TU Dresden, we have carried out a collaborative measurement campaign to collect data for modeling flotation subprocesses under varying hydrodynamic and reagent conditions using a laboratory scale flotation cell and a binary pyrite-quartz particle system. Froth phase measurements included the recording of the froth height through the transparent side wall of the flotation cell and imaging of the froth surface as well as foamability measurements of feed and tailing samples by means of dynamic foam analysis and measurement of the liquid fraction of the froth based on its electrical conductivity. Preliminary results show a significant change in froth properties during the flotation process from a particle-laden froth to finer bubbles containing fewer particles. Further data analysis is planned to investigate the influence of frother and collector concentrations as well as air flow rate and impeller tip speed on the foamability and froth height, impacting the recovery and grade of minerals. Such joint froth studies between the Institute of Fluid Dynamics and HIF belong to the sciences cases perspectively to be intensified by CeRI2, one of the HZDR research infrastructure projects.

The liquid fraction of foam is an important quantity in engineering process control and essential to interpret foam rheology. Established measurement tools for the liquid fraction of foam, such as optical measurement or radiography techniques as well as weighing the foam, are mostly laboratory-based, whereas conductivity-based measurements are limited to the global measurement without detailed spatial information of liquid fraction. In this work, which combines both types of measurement techniques, the conductivity-based wire-mesh sensor is compared with neutron radiography. We found a linear dependency between the liquid fraction of the foam and the wire-mesh readings with a statistical deviation less than 15%. However, the wire-mesh sensor systematically overestimates the liquid fraction which we attribute to liquid bridge formation between the wires.

In mineral processing, froth flotation is based on recovering valuable mineral particles by means of the overflowing froth. Industrial-scale froth flotations cells are typically equipped with optical measurement systems, which monitor bubble sizes and flow velocities at the froth surface. However, the velocity profile of the overflowing froth underneath its free surface is not accessible by optical observation. The present study combines X-ray radiography and particle tracking velocimetry in a laboratory-scale experiment, aiming to measure local flow velocities within an opticially opaque foam at a horizontal overflow. For this purpose, we prepared custom-tailored tracer particles: light- weight tetrahedra with an edge length of 4 mm were 3D-printed from a polymer material, and metal beads of 0.5 mm in diameter glued at each corner of a tetrahedron served as radiopaque features. In parallel to the velocity measurements by means of X-ray particle tracking, we determined the liquid fraction of the overflowing foam by electric conductivity measurements using electrode pairs. The experiment was performed with aqeuous foams of two different surfactant concentrations, but similar bubble size range and superficial gas velocity, yielding around 10 % liquid fraction near the overflow. Employing the particles as tools for flow tracing in X-ray image sequences, we identified an unexpected velocity maximum underneath the free surface of the overflowing foam. In a sequel, we will compare the X-ray radiographic measurements with optical measurements of the foam flow velocity through a transparent wall and at the free surface.

Batteries with liquid metal electrodes are attractive candidates for sustainable energy storage applications due to low manufacturing cost as well as high recyclability. For broad applications, these batteries should be developed for lower operating temperature, higher cell voltage, and membrane-free cell configuration. Here, we demonstrate a new type of membrane-free electrochemical energy storage system relying on liquid alkali metals and iodide. As a proof-of-concept study, membrane-free alkali metal-iodide (A-AI) batteries were constructed by a facile cell assembly introducing current collectors, LiI-LiCl-KI-CsI salt mixture, and an insulator without relying on solid-state mediums for separating electrolytes. For the initial assembly, no active electrode materials were required since they can be naturally formed during battery operation. Despite the unoptimized cell construction, the membrane-free A-AI batteries showed promising electrochemical performance such as voltage efficiency of ca. 40 % at 500 mA/cm2, maximum specific energy of 34.2 Wh/kg with an energy efficiency of 59 % for a charging/discharging period of 5.8 h and reliable stability for 250 cycles. Even without ion-selective membranes, we observed a relatively low self-discharge rate of 3.56 mA/cm2, which implies the possibility of an iodine-concentrated layer at the bottom of the cell. This was further supported by post-mortem analyses using neutron radiography. Additionally, X-ray photoemission spectroscopy was performed to identify the changes in the iodine concentration in the cell.

The flow behaviour of liquid foam is of central importance in froth flotation for mineral processing. Flotation separates valuable mineral particles from gangue material based on the surface wettability. To this end, the solids are finely ground and suspended in an aqueous solution with flotation reagents. In aerated flotations cells, gas bubbles selectively attach to the hydrophobic mineral particles, rise to the surface, and form a froth. To recover the valuables, they are transported out of the flotation cell with the froth. In flotation plants, the recovery of solid and liquid is monitored by optical observation of the overflowing froth. However, this monitoring is limited to the free surface of the particle-laden froth. Aiming for detailed insights into the flow behaviour underneath the surface-near foam bubbles, the laboratory-scale experiment in this work investigates the velocity field of an overflowing foam in combined optical and X-ray measurements. For this purpose, foam was generated continuously, moved similar to a plug-flow in a vertical channel with rectangular cross-section, and flowed off over a one-sided horizontal weir into the open surrounding. The imaging measurements focused on the foam flow in the region of interest around the weir. Simultaneously, the liquid fraction of the foam was monitored by measuring its electric conductivity between electrode pairs mounted near the weir. We used aqueous foams of two different surfactant concentrations but similar bubble size range and superficial gas velocity, yielding around 10 % liquid fraction. The optical measurements carried out through the transparent side wall of the flow channel as well as at the free surface of the overflowing foam. They captured light reflections on the foam bubbles were analysed by an adapted particle image velocimetry algorithm. While the opacity of the foam limits optical measurements to the wall- or surface-near foam bubbles, our approach of X-ray particle tracking velocim

X-ray radiographic imaging is an efficient tool for investigating flow phenomena and solidification processes in optically opaque metallic alloys. This contribution is an overview of the latest advances in in-situ radiographic experiments made by the authors, as well as recent applications, including magnetohydrodynamic systems. We investigated a range of phenomena, such as bubble flow in liquid metal under an applied magnetic field, collective bubble dynamics, particle flow in liquid metal channels, and mesoscale solidification of alloys. Radiography measurements in liquid/solidified metal experiments are inevitably performed under adverse conditions of low signal-to-noise ratio, low image contrast, scattering, etc. To extract meaningful information from experimental data we combine both well-known methodology of data processing and our original codes. Examples of image analysis and results of in-situ experiments performed with low melting point alloys are presented and discussed in this contribution. A focus of these experiments is exploring scaled-down representative systems of industrial processes in metallic alloys.

The cost-efficient production of green hydrogen using renewable energies requires next-generation proton exchange membrane (PEM) electrolysers to be operated at higher current density. Under this new operating condition, the elevated temperature of the ultra-pure water and its supersaturation with oxygen on the anode side have strong effects on the formation and transport of gas bubbles. The resulting gas-liquid two-phase flow through the porous transport layer at the membrane electrode assembly is characterised by up to 50 % gas fraction, which is exceptionally high. Such a foam-like flow within the porous medium is not accessible by optical measurements. Instead, we performed imaging flow measurements by means of time-resolved radiography using polychromatic X-rays as well as thermal neutrons at 100 frames per second imaging frame rate. On a laboratory scale, we aimed to study the bubble transport by mapping the local gas fraction distribution over time. This conference contribution presents two model experiments with open-porous metal and polymer foams, namely made of nickel and polyurethane, showcasing the advantages but also limitations of X-ray and neutron radiography for investigating bubble transport phenomena within such foam structures. In both experiments, foam samples of approximately 70 mm x 70 mm in width and height were sandwiched between the X-ray- or neutron-transparent front and back windows of a vessel filled with deionised water. As neutrons are strongly attenuated in water, the thickness of the water-filled vessel and the foam sample were set to 5 mm along the beam direction in all measurements. Bubbles were generated continuously by injecting compressed air at different but constant volumetric flow rates through a single hollow needle releasing the bubbles directly into the water-soaked foam. Based on calibration radiographs acquired both in the absence and presence of water, quantitative image analysis yielded a pixelwise mapping of the gas fr

Raw data from experiments with membrane-free alkali metal-iodide cells containing XPS results, phase-diagram calculations, neutron radiography images, electrochemical cycling data, and electron microscope images of the carbon felt used.

Froth flow is of central importance for mineral processing by froth flotation. In flotation plants, the recovery of solid mineral particles and liquid from the overflowing froth is monitored by optical observation and, therefore, limited to the froth’s free surface. The laboratory-scale experiment in this work investigates the flow behaviour of an aqueous foam at a horizontal overflow (Fig. 1) 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) 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 (Fig. 1). Owing to their shape and the light-weight 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 sub-jected 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.

Neutron radiography is a useful tool for researching opaque multi phase flow such as foam and froth.

Transport of liquid through the foam is governed by the mutual effects of capillary, gravitational, and inertia forces [Koehler, S. A. et. al. (2000)]. This process defines the distribution of liquid in foam and is essential for industrial applications, e.g. production of polymeric and metal foams, flotation etc. S. Neethling [Neethling, S. J. (2006)] have shown that sheared foam could not anymore be considered as an isotropic media, and the direction of a drainage flow distinct from the sense of a gravity vector. Thus, a non-uniform distribution of liquid in the foam is present. This effect, for instance, has a major impact on a formation of convective rolls in foam [Heitkam, S., & Eckert, K. (2021)].

After coarsening and coalescence, foam drainage is one of the processes that dynamically influence foams. It is therefore of general interest to understand it in its principle behaviour. Liquid drainage is typically described by the unsteady, three-dimensional drainage equation [Verbist, 1996]. However, apart from optical observation in a Hele-Shaw cell [Hutzler, 2005], unsteady and multi-dimensional measurement of liquid fraction distribution is scarcely approached. Here, two-dimensional foam drainage experiments and simulations were carried out to validate the horizontal terms of foam drainage equation and to show its limitations. The two-dimensional liquid fraction distribution in steady, dynamic and periodic drainage experiments was measured with neutron radiography [Heitkam, 2018]. In particular, the damping character of the foam drainage was quantified as a function of different frequencies and amplitudes. This yields guidelines for forced-drainage experiments with peristaltic pumps.

Schaum und dessen Strömungsverhalten sind von zentraler Bedeutung bei der Schaumflotation zur Mineralaufbereitung. Die zu gewinnenden Mineralpartikel lagern sich an aufsteigenden Gasblasen an und werden mit dem Schaum aus der Flotationszelle heraustransportiert. In industriellen Flotationsanlagen wird die Rückgewinnung von Feststoff- und Flüssigphase aus der überlaufenden Schaumströmung mittels optischer Messtechnik überwacht und ist daher auf die freie Oberfläche des partikelbeladenen Schaums beschränkt. Die vorliegende Arbeit untersucht das Strömungsverhalten eines wässrigen Schaums an einem Überlauf vergleichend mittels optischer und Röntgen-Messungen. Der Schaum wurde kontinuierlich erzeugt, strömte in vertikaler Richtung durch einen Kanal mit quadratischem Querschnitt und floss durch einen einseitigen horizontalen Überlauf in die freie Umgebung. Die bildgebenden Strömungsmessungen fokussierten sich auf den Schaum im Bereich des Überlaufs. Gleichzeitig wurde hier der Flüssigkeitsanteil des Schaums mittels Messung der elektrischen Leitfähigkeit zwischen jeweils zwei Elektroden bestimmt. Die optischen Messungen erfolgten einerseits durch die transparente Kanalwand und andererseits an der freien Oberfläche des überlaufenden Schaums. Die dortigen Strömungsgeschwindigkeiten wurden mittels angepasster PIV-Algorithmen ausgewertet, welche Lichtreflexionen auf den Schaumblasen als Messinformation nutzten. Aufgrund der Undurchsichtigkeit des Schaums erfassen diese optischen Messungen nur die oberflächennahen Schaumblasen. Unsere Variante der Röntgen-Radiographie mit maßgeschneiderten Tracer-Partikeln (X-PTV) gibt Aufschluss über die drei-dimensionale Schaumströmung. Die in dieser Arbeit verwendeten Tracer bestanden aus einer 3D-gedruckten polymeren Trägerstruktur in Form eines Tetraeders mit insgesamt vier kleinen Metallkügelchen an dessen Ecken. Dank der Tetraeder-Form und des geringen Gewichts des Materialverbunds hafteten die Tracer in der Schaumstruktur und wurden in

Schaum und dessen Strömungsverhalten sind von zentraler Bedeutung bei der Schaumflotation zur Mineralaufbereitung. Die zu gewinnenden Mineralpartikel lagern sich an aufsteigenden Gasblasen an und werden mit dem Schaum aus der Flotationszelle heraustransportiert. In industriellen Flotationsanlagen wird die Rückgewinnung von Feststoff- und Flüssigphase aus der überlaufenden Schaumströmung mittels optischer Messtechnik überwacht und ist daher auf die freie Oberfläche des partikelbeladenen Schaums beschränkt. Die vorliegende Arbeit untersucht das Strömungsverhalten eines wässrigen Schaums an einem Überlauf vergleichend mittels optischer und Röntgen-Messungen. Der Schaum wurde kontinuierlich erzeugt, strömte in vertikaler Richtung durch einen Kanal mit quadratischem Querschnitt und floss durch einen einseitigen horizontalen Überlauf in die freie Umgebung. Die bildgebenden Strömungsmessungen fokussierten sich auf den Schaum im Bereich des Überlaufs. Gleichzeitig wurde hier der Flüssigkeitsanteil des Schaums mittels Messung der elektrischen Leitfähigkeit zwischen jeweils zwei Elektroden bestimmt. Die optischen Messungen erfolgten einerseits durch die transparente Kanalwand und andererseits an der freien Oberfläche des überlaufenden Schaums. Die dortigen Strömungsgeschwindigkeiten wurden mittels angepasster PIV-Algorithmen ausgewertet, welche Lichtreflexionen auf den Schaumblasen als Messinformation nutzten. Aufgrund der Undurchsichtigkeit des Schaums erfassen diese optischen Messungen nur die oberflächennahen Schaumblasen. Unsere Variante der Röntgen-Radiographie mit maßgeschneiderten Tracer-Partikeln (X-PTV) gibt Aufschluss über die drei-dimensionale Schaumströmung. Die in dieser Arbeit verwendeten Tracer bestanden aus einer 3D-gedruckten polymeren Trägerstruktur in Form eines Tetraeders mit insgesamt vier kleinen Metallkügelchen an dessen Ecken. Dank der Tetraeder-Form und des geringen Gewichts des Materialverbunds hafteten die Tracer in der Schaumstruktur und wurden in

Multiphase flows of dispersed gas bubbles and solid particles in liquid metals are hardly to investigate in situ in industrial-scale metallurgical reactors. Laboratory-scale model experiments with low-melting metal alloys have proven very beneficial for radiographic flow investigations. To extend previous experimental studies that were focussed on either bubble or particle flows in liquid gallium and its alloys, we used neutron radiography for visualising liq-uid-liquid two-phase flows of silicone oil drops in the eutectic gallium-tin alloy. We determined the average size of the ascending drops, measured the velocity of each drop along its motion path, and estimated dimensionless numbers to compare drop and bubble characteristics. Here, we exemplarily present the results for drops of 4 mm in diameter, which may serve as a valuable basis for future experiments and simulations with drops and particles in the liquid metal.

Liquid drainage through foam is driven by gravity, capillary, and, to a lesser extent, viscous forces. In the of stress on the foam, the liquid distributes uniformly, however, imposed stress changes the alignment of the foam’s structural elements. Previous numerical simulations [1] predicted that a vertical drainage flow will be deflected horizontally if the foam is sheared. We investigated such phenomena by measuring the distribution of liquid fraction within a foam formed in a flat rectangular cell. The foam was subjected to shear stress under a forced liquid supply at the top of the cell. Two dimensional neutron radiography images of stress-free and sheared foam were analyzed to extract measurements of liquid content. Deflections in the distribution of the drainage liquid were detected, and found to be positively correlated with increasing foam shear. To the best of our knowledge, this is the first experimental observation of anisotropic drainage in a liquid foam.

Multiphase flows of dispersed gas bubbles and solid particles in liquid metals are hardly to investigate in situ in industrial-scale metallurgical reactors. Laboratory-scale model experiments with low-melting metal alloys have proven very beneficial for radiographic flow investigations. To extend previous experimental studies that were focussed on either bubble or particle flows in liquid gallium and its alloys, we used neutron radiography for visualising liq-uid-liquid two-phase flows of silicone oil drops in the eutectic gallium-tin alloy. We determined the average size of the ascending drops, measured the velocity of each drop along its motion path, and estimated dimensionless numbers to compare drop and bubble characteristics. Here, we exemplarily present the results for drops of 4 mm in diameter, which may serve as a valuable basis for future experiments and simulations with drops and particles in the liquid metal.

This paper demonstrates particle tracking velocimetry performed for a model system wherein particle-laden liquid metal flow around a cylindrical obstacle was studied. We present the image processing methodology developed for particle detection in images with disparate and often low signal- and contrast-to-noise ratios, and the application of our MHT-X tracing algorithm for particle trajectory reconstruction for the wake flow around the obstacle. Preliminary results indicate that the utilized methods enable consistent particle detection and recovery of long, representative particle trajectories with high confidence. However, we also underline the necessity of implementing a more advanced particle position extrapolation approach for increased tracking accuracy. Satisfactory tracking accuracy can be inferred from the fact that the fluctuations in the measured particle velocity are dominated by frequencies that agree sufficiently well with the expected frequencies of the cylinder wake.

Schaum und dessen Strömungsverhalten sind von zentraler Bedeutung bei der Schaumflotation zur Mineralaufbereitung. Die zu gewinnenden Mineralpartikel lagern sich an aufsteigenden Gasblasen an und werden mit dem Schaum aus der Flotationszelle heraustransportiert. In industriellen Flotationsanlagen wird die Rückgewinnung von Feststoff- und Flüssigphase aus der überlaufenden Schaumströmung mittels optischer Messtechnik überwacht und ist daher auf die freie Oberfläche des partikelbeladenen Schaums beschränkt. Die vorliegende Arbeit untersucht das Strömungsverhalten eines wässrigen Schaums an einem Überlauf vergleichend mittels optischer und Röntgen-Messungen. Der Schaum wurde kontinuierlich erzeugt, strömte in vertikaler Richtung durch einen Kanal mit quadratischem Querschnitt und floss durch einen einseitigen horizontalen Überlauf in die freie Umgebung. Die bildgebenden Strömungsmessungen fokussierten sich auf den Schaum im Bereich des Überlaufs. Gleichzeitig wurde hier der Flüssigkeitsanteil des Schaums mittels Messung der elektrischen Leitfähigkeit zwischen jeweils zwei Elektroden bestimmt. Die optischen Messungen erfolgten einerseits durch die transparente Kanalwand und andererseits an der freien Oberfläche des überlaufenden Schaums. Die dortigen Strömungsgeschwindigkeiten wurden mittels angepasster PIV-Algorithmen ausgewertet, welche Lichtreflexionen auf den Schaumblasen als Messinformation nutzten. Aufgrund der Undurchsichtigkeit des Schaums erfassen diese optischen Messungen nur die oberflächennahen Schaumblasen. Unsere Variante der Röntgen-Radiographie mit maßgeschneiderten Tracer-Partikeln (X-PTV) gibt Aufschluss über die drei-dimensionale Schaumströmung. Die in dieser Arbeit verwendeten Tracer bestanden aus einer 3D-gedruckten polymeren Trägerstruktur in Form eines Tetraeders mit insgesamt vier kleinen Metallkügelchen an dessen Ecken. Dank der Tetraeder-Form und des geringen Gewichts des Materialverbunds hafteten die Tracer in der Schaumstruktur und wurden in

Neutron radiography is a useful tool for researching opaque multi phase flow such as foam and froth.

Transport of liquid through the foam is governed by the mutual effects of capillary, gravitational, and inertia forces [Koehler, S. A. et. al. (2000)]. This process defines the distribution of liquid in foam and is essential for industrial applications, e.g. production of polymeric and metal foams, flotation etc. S. Neethling [Neethling, S. J. (2006)] have shown that sheared foam could not anymore be considered as an isotropic media, and the direction of a drainage flow distinct from the sense of a gravity vector. Thus, a non-uniform distribution of liquid in the foam is present. This effect, for instance, has a major impact on a formation of convective rolls in foam [Heitkam, S., & Eckert, K. (2021)].

Liquid drainage through foam is driven by gravity, capillary, and, to a lesser extent, viscous forces. In the of stress on the foam, the liquid distributes uniformly, however, imposed stress changes the alignment of the foam’s structural elements. Previous numerical simulations [1] predicted that a vertical drainage flow will be deflected horizontally if the foam is sheared. We investigated such phenomena by measuring the distribution of liquid fraction within a foam formed in a flat rectangular cell. The foam was subjected to shear stress under a forced liquid supply at the top of the cell. Two dimensional neutron radiography images of stress-free and sheared foam were analyzed to extract measurements of liquid content. Deflections in the distribution of the drainage liquid were detected, and found to be positively correlated with increasing foam shear. To the best of our knowledge, this is the first experimental observation of anisotropic drainage in a liquid foam.

Froth flow is of central importance for mineral processing by froth flotation. In flotation plants, the recovery of solid mineral particles and liquid from the overflowing froth is monitored by optical observation and, therefore, limited to the froth’s free surface. The laboratory-scale experiment in this work investigates the flow behaviour of an aqueous foam at a horizontal overflow (Fig. 1) 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) 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 (Fig. 1). Owing to their shape and the light-weight 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 sub-jected 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.

Schaum und dessen Strömungsverhalten sind von zentraler Bedeutung bei der Schaumflotation zur Mineralaufbereitung. Die zu gewinnenden Mineralpartikel lagern sich an aufsteigenden Gasblasen an und werden mit dem Schaum aus der Flotationszelle heraustransportiert. In industriellen Flotationsanlagen wird die Rückgewinnung von Feststoff- und Flüssigphase aus der überlaufenden Schaumströmung mittels optischer Messtechnik überwacht und ist daher auf die freie Oberfläche des partikelbeladenen Schaums beschränkt. Die vorliegende Arbeit untersucht das Strömungsverhalten eines wässrigen Schaums an einem Überlauf vergleichend mittels optischer und Röntgen-Messungen. Der Schaum wurde kontinuierlich erzeugt, strömte in vertikaler Richtung durch einen Kanal mit quadratischem Querschnitt und floss durch einen einseitigen horizontalen Überlauf in die freie Umgebung. Die bildgebenden Strömungsmessungen fokussierten sich auf den Schaum im Bereich des Überlaufs. Gleichzeitig wurde hier der Flüssigkeitsanteil des Schaums mittels Messung der elektrischen Leitfähigkeit zwischen jeweils zwei Elektroden bestimmt. Die optischen Messungen erfolgten einerseits durch die transparente Kanalwand und andererseits an der freien Oberfläche des überlaufenden Schaums. Die dortigen Strömungsgeschwindigkeiten wurden mittels angepasster PIV-Algorithmen ausgewertet, welche Lichtreflexionen auf den Schaumblasen als Messinformation nutzten. Aufgrund der Undurchsichtigkeit des Schaums erfassen diese optischen Messungen nur die oberflächennahen Schaumblasen. Unsere Variante der Röntgen-Radiographie mit maßgeschneiderten Tracer-Partikeln (X-PTV) gibt Aufschluss über die drei-dimensionale Schaumströmung. Die in dieser Arbeit verwendeten Tracer bestanden aus einer 3D-gedruckten polymeren Trägerstruktur in Form eines Tetraeders mit insgesamt vier kleinen Metallkügelchen an dessen Ecken. Dank der Tetraeder-Form und des geringen Gewichts des Materialverbunds hafteten die Tracer in der Schaumstruktur und wurden in

After coarsening and coalescence, foam drainage is one of the processes that dynamically influence foams. It is therefore of general interest to understand it in its principle behaviour. Liquid drainage is typically described by the unsteady, three-dimensional drainage equation [Verbist, 1996]. However, apart from optical observation in a Hele-Shaw cell [Hutzler, 2005], unsteady and multi-dimensional measurement of liquid fraction distribution is scarcely approached. Here, two-dimensional foam drainage experiments and simulations were carried out to validate the horizontal terms of foam drainage equation and to show its limitations. The two-dimensional liquid fraction distribution in steady, dynamic and periodic drainage experiments was measured with neutron radiography [Heitkam, 2018]. In particular, the damping character of the foam drainage was quantified as a function of different frequencies and amplitudes. This yields guidelines for forced-drainage experiments with peristaltic pumps.

This contribution is an overview of the latest advances in image processing made by the authors, as well as recent and potential applications, including magnetohydrodynamic systems. Contemporary research of two-phase liquid metal flow requires state of the art experimental methods to probe downscaled representative systems. Among these methods are dynamic neutron and X-ray radiography which have applications in studying bubble flow in liquid metal affected by applied magnetic field [1], bubble collective dynamics in Hele-Shaw liquid metal cells [2], particle flow in liquid metal channels [3] and mesoscale solidification of metals under applied magnetic field [4]. Pushing the boundaries, these measurements are inevitably performed under adverse conditions: low signal-to-noise ratio owing to high frame rates (relative to the source flux) required to capture the physics of interest, but also low image resolution, image artefacts, scattering, etc. Therefore, to extract meaningful information from experimental data and study the underlying processes, appropriate image processing methods and tools are required. Development of such tools is also motivated by very limited (for most researchers) access to high-end neutron and X-ray imaging setups and thus one must make the most of data acquired during limited beamtimes. Examples of applications of our solutions to experimental data from neutron and X-ray imaging are shown in Figures 1-4.

In metallurgical processing, non-metallic inclusions in metallic materials are one highly relevant challenge. Bubble injection into molten metals boosts the inclusion control and removal, thus enhancing metal homogenisation and purification. Although this principle of bubble flotation has been used for a long time, the effects of bubble-inclusion interactions in molten metals are not yet well researched. Imaging measurements of multiphase metal flows are challenging for two main reasons: the metals’ high melting temperatures, and their opaqueness for visible light. This work focuses on X-ray and neutron radiographic experiments employing low-melting gallium alloys laden with model particles smaller than 1 mm in diameter. Both, bubbles and particles, are visualised simultaneously with high spatial and temporal resolution to analyse their motions by tracking algorithms. We demonstrate the capability of time-resolved X-ray and neutron radiography to image multiphase flows in particle-laden optically opaque liquid metal, thus contributing to pave the way for systematic investigations on bubble-inclusion interactions in molten metals.

Multi-phase flows of small solid particles and gas bubbles in optically opaque fluids play a key role in both mineral and metallurgical processing, which use the principle of froth flotation and bubble flotation, respectively. To gain visual insight into such particle-laden multi-phase flows, this dissertation investigates the application of radiographic techniques, employing both X-rays and neutron radiation. Lab-scale experiments are performed with model particles in liquid foams and liquid metals, focussing on the time-resolved measurement of the particles’ motion in the multi-phase flows, aiming for a sufficient contrast-to-noise ratio in the X-ray or neutron image sequences. The model experiments in this dissertation demonstrate the capabilities of X-ray and neutron radiography to image multi-phase flow in particle-laden and optically opaque fluids, especially to measure the motions of small particles with high spatial and temporal resolution. X-ray radiography enables to track custom-tailored tracer particles acting as tools for experimental investigations of flow phenomena in three-dimensional liquid foams. Both radiographic techniques supplement each other for imaging measurements of multi-phase flows with gas bubbles and solid particles in liquid metals. However, to visualise smallest model particles in liquid metal flows, neutron radiography proves to be the more promising technique compared to X-ray radiography. All in all, this dissertation contributes to paving the way for systematic radiographic measurements and further studies of particle-laden flows in optically opaque fluids.

In metallurgical processing, non-metallic inclusions in metallic materials are one highly relevant challenge. Bubble injection into molten metals boosts the inclusion control and removal, thus enhancing metal homogenisation and purification. Although this principle of bubble flotation has been used for a long time, the effects of bubble-inclusion interactions in molten metals are not yet well researched. Imaging measurements of multiphase metal flows are challenging for two main reasons: the metals’ high melting temperatures, and their opaqueness for visible light. This work focuses on X-ray and neutron radiographic experiments employing low-melting gallium alloys laden with model particles smaller than 1 mm in diameter. Both, bubbles and particles, are visualised simultaneously with high spatial and temporal resolution to analyse their motions by tracking algorithms. We demonstrate the capability of time-resolved X-ray and neutron radiography to image multiphase flows in particle-laden optically opaque liquid metal, thus contributing to pave the way for systematic investigations on bubble-inclusion interactions in molten metals.

This contribution is an overview of the latest advances in image processing made by the authors, as well as recent and potential applications, including magnetohydrodynamic systems. Contemporary research of two-phase liquid metal flow requires state of the art experimental methods to probe downscaled representative systems. Among these methods are dynamic neutron and X-ray radiography which have applications in studying bubble flow in liquid metal affected by applied magnetic field [1], bubble collective dynamics in Hele-Shaw liquid metal cells [2], particle flow in liquid metal channels [3] and mesoscale solidification of metals under applied magnetic field [4]. Pushing the boundaries, these measurements are inevitably performed under adverse conditions: low signal-to-noise ratio owing to high frame rates (relative to the source flux) required to capture the physics of interest, but also low image resolution, image artefacts, scattering, etc. Therefore, to extract meaningful information from experimental data and study the underlying processes, appropriate image processing methods and tools are required. Development of such tools is also motivated by very limited (for most researchers) access to high-end neutron and X-ray imaging setups and thus one must make the most of data acquired during limited beamtimes. Examples of applications of our solutions to experimental data from neutron and X-ray imaging are shown in Figures 1-4.

In metallurgical processing, non-metallic inclusions in metallic materials are one highly relevant challenge. Bubble injection into molten metals boosts the inclusion control and removal, thus enhancing metal homogenisation and purification. Although this principle of bubble flotation has been used for a long time, the effects of bubble-inclusion interactions in molten metals are not yet well researched. Imaging measurements of multiphase metal flows are challenging for two main reasons: the metals’ high melting temperatures, and their opaqueness for visible light. This work focuses on X-ray and neutron radiographic experiments employing low-melting gallium alloys laden with model particles smaller than 1 mm in diameter. Both, bubbles and particles, are visualised simultaneously with high spatial and temporal resolution to analyse their motions by tracking algorithms. We demonstrate the capability of time-resolved X-ray and neutron radiography to image multiphase flows in particle-laden optically opaque liquid metal, thus contributing to pave the way for systematic investigations on bubble-inclusion interactions in molten metals.

Multi-phase flows of small solid particles and gas bubbles in optically opaque fluids play a key role in both mineral and metallurgical processing, which use the principle of froth flotation and bubble flotation, respectively. To gain visual insight into such particle-laden multi-phase flows, this dissertation investigates the application of radiographic techniques, employing both X-rays and neutron radiation. Lab-scale experiments are performed with model particles in liquid foams and liquid metals, focussing on the time-resolved measurement of the particles’ motion in the multi-phase flows, aiming for a sufficient contrast-to-noise ratio in the X-ray or neutron image sequences. The model experiments in this dissertation demonstrate the capabilities of X-ray and neutron radiography to image multi-phase flow in particle-laden and optically opaque fluids, especially to measure the motions of small particles with high spatial and temporal resolution. X-ray radiography enables to track custom-tailored tracer particles acting as tools for experimental investigations of flow phenomena in three-dimensional liquid foams. Both radiographic techniques supplement each other for imaging measurements of multi-phase flows with gas bubbles and solid particles in liquid metals. However, to visualise smallest model particles in liquid metal flows, neutron radiography proves to be the more promising technique compared to X-ray radiography. All in all, this dissertation contributes to paving the way for systematic radiographic measurements and further studies of particle-laden flows in optically opaque fluids.

In this work, we introduce a novel approach to measure the flow velocity of liquid foam by tracking custom-tailored 3D-printed tracers in X-ray radiography. In contrast to optical observations of foam flow in flat cells, the measurement depth equals 100mm in X-ray beam direction. Light-weight tracers of millimetric size and tetrapod-inspired shape are additively manufactured from stainless steel powder by selective laser melting. Matching with the foam structure and bubble size, these tracers follow the foam flow minimally invasively. An X-ray beam passes through the radiotransparent foam channel and is detected by an X-ray image intensifier. The X-ray transmission images show the two-dimensional projections of the radiopaque tracers. Employing particle tracking velocimetry algorithms, the tracer trajectories are measured with both high spatial (0.2 mm) and temporal (25 fps) resolution. Fine-pored and coarse-pored liquid foam flow of different velocities are studied in a partly curved channel with rectangular cross section. The simultaneous time-resolved measurement of the tracers' translational motion and their intrinsic rotation reveal both the local velocity and vorticity of the foam flow. In the semi-circular curved channel section, the rigid-body-like flow pattern is investigated. Moreover, a relaxation of the foam structure in the transition zone between straight and curved section is observed.

In this work, we introduce a novel approach to measure the flow velocity of liquid foam by tracking custom-tailored 3D-printed tracers in X-ray radiography. In contrast to optical observations of foam flow in flat cells, the measurement depth equals 100mm in X-ray beam direction. Light-weight tracers of millimetric size and tetrapod-inspired shape are additively manufactured from stainless steel powder by selective laser melting. Matching with the foam structure and bubble size, these tracers follow the foam flow minimally invasively. An X-ray beam passes through the radiotransparent foam channel and is detected by an X-ray image intensifier. The X-ray transmission images show the two-dimensional projections of the radiopaque tracers. Employing particle tracking velocimetry algorithms, the tracer trajectories are measured with both high spatial (0.2 mm) and temporal (25 fps) resolution. Fine-pored and coarse-pored liquid foam flow of different velocities are studied in a partly curved channel with rectangular cross section. The simultaneous time-resolved measurement of the tracers' translational motion and their intrinsic rotation reveal both the local velocity and vorticity of the foam flow. In the semi-circular curved channel section, the rigid-body-like flow pattern is investigated. Moreover, a relaxation of the foam structure in the transition zone between straight and curved section is observed.

Ladle metallurgy treatment affects the chemical composition and the impurities in molten steel. To remove non-metallic inclusions, gas injection into the ladle and intense stirring by bubbly flows are essential in the refining process. This paper reports on a model experiment that provides an insight into the bubble – particle interaction in liquid metal at room temperature. We apply neutron radiography as imaging technique for particle-laden liquid metal flow around a cylindrical obstacle representing a single rising bubble. The experimental setup is tailored to both the measurement principle of neutron transmission imaging and the design of the disc-type induction pump driving the flow. A liquid metal loop of 30 mm x 3 mm rectangular cross section is filled with low-melting gallium-tin alloy. Gadolinium oxide particles (0.3 – 0.5mm) are employed because of their superior neutron attenuation compared to liquid gallium-tin. The neutron image sequences visualise the particle trajectories in the opaque liquid metal with high temporal resolution (100 fps). Up- and downstream the cylindrical obstacle, we analyse the velocity field as a function of the pump’s rotational speed by particle image velocimetry (PIV). The time-averaged particle velocity measured by PIV is lower than the circumferential velocity of the pump’s discs. This velocity deficit arises from the particles’ buoyancy and the pressure drop in the liquid metal loop. In the further analysis of these neutron image data, we will focus on the fluid flow in the wake of the cylindrical obstacle.

In this work, we introduce a novel approach to measure the flow velocity of liquid foam by tracking custom-tailored 3D-printed tracers in X-ray radiography. In contrast to optical observations of foam flow in flat cells, the measurement depth equals 100mm in X-ray beam direction. Light-weight tracers of millimetric size and tetrapod-inspired shape are additively manufactured from stainless steel powder by selective laser melting. Matching with the foam structure and bubble size, these tracers follow the foam flow minimally invasively. An X-ray beam passes through the radiotransparent foam channel and is detected by an X-ray image intensifier. The X-ray transmission images show the two-dimensional projections of the radiopaque tracers. Employing particle tracking velocimetry algorithms, the tracer trajectories are measured with both high spatial (0.2 mm) and temporal (25 fps) resolution. Fine-pored and coarse-pored liquid foam flow of different velocities are studied in a partly curved channel with rectangular cross section. The simultaneous time-resolved measurement of the tracers' translational motion and their intrinsic rotation reveal both the local velocity and vorticity of the foam flow. In the semi-circular curved channel section, the rigid-body-like flow pattern is investigated. Moreover, a relaxation of the foam structure in the transition zone between straight and curved section is observed.

Ladle metallurgy treatment affects the chemical composition and the impurities in molten steel. To remove non-metallic inclusions, gas injection into the ladle and intense stirring by bubbly flows are essential in the refining process. This paper reports on a model experiment that provides an insight into the bubble – particle interaction in liquid metal at room temperature. We apply neutron radiography as imaging technique for particle-laden liquid metal flow around a cylindrical obstacle representing a single rising bubble. The experimental setup is tailored to both the measurement principle of neutron transmission imaging and the design of the disc-type induction pump driving the flow. A liquid metal loop of 30 mm x 3 mm rectangular cross section is filled with low-melting gallium-tin alloy. Gadolinium oxide particles (0.3 – 0.5mm) are employed because of their superior neutron attenuation compared to liquid gallium-tin. The neutron image sequences visualise the particle trajectories in the opaque liquid metal with high temporal resolution (100 fps). Up- and downstream the cylindrical obstacle, we analyse the velocity field as a function of the pump’s rotational speed by particle image velocimetry (PIV). The time-averaged particle velocity measured by PIV is lower than the circumferential velocity of the pump’s discs. This velocity deficit arises from the particles’ buoyancy and the pressure drop in the liquid metal loop. In the further analysis of these neutron image data, we will focus on the fluid flow in the wake of the cylindrical obstacle.

In this work, we introduce a novel approach to measure the flow velocity of liquid foam by tracking custom-tailored 3D-printed tracers in X-ray radiography. In contrast to optical observations of foam flow in flat cells, the measurement depth equals 100mm in X-ray beam direction. Light-weight tracers of millimetric size and tetrapod-inspired shape are additively manufactured from stainless steel powder by selective laser melting. Matching with the foam structure and bubble size, these tracers follow the foam flow minimally invasively. An X-ray beam passes through the radiotransparent foam channel and is detected by an X-ray image intensifier. The X-ray transmission images show the two-dimensional projections of the radiopaque tracers. Employing particle tracking velocimetry algorithms, the tracer trajectories are measured with both high spatial (0.2 mm) and temporal (25 fps) resolution. Fine-pored and coarse-pored liquid foam flow of different velocities are studied in a partly curved channel with rectangular cross section. The simultaneous time-resolved measurement of the tracers' translational motion and their intrinsic rotation reveal both the local velocity and vorticity of the foam flow. In the semi-circular curved channel section, the rigid-body-like flow pattern is investigated. Moreover, a relaxation of the foam structure in the transition zone between straight and curved section is observed.