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The contactless inductive flow tomography (CIFT) allows to visualize the mean flow structure in liquid metals by measuring the flow induced magnetic field perturbations under the influence of one, or several, applied magnetic fields. The reliable measurement of these very small field changes, and the involved mathematics to solve the inverse problem, are the main challenges for this flow inference method. We demonstrate the applicability of CIFT for various model experiments devoted to the continuous casting process, by employing a new measurement system using induction coils and AC excitation. This enables the determination of the flow structure even in the presence of a strong static magnetic brake field which is often used in continuous casting for controlling the flow in the mold. Additionally, we present preliminary results of CIFT applied to a thermally driven flow with some similarity to Czochralski silicon crystal growth. Due to the low velocities in the order of 1 cm/s, the dynamic range of the measurement system has to be enhanced by about one order of magnitude in comparison with the continuous casting application.

The contactless inductive flow tomography (CIFT) allows to visualize the mean flow structure in liquid metals by measuring the flow induced magnetic field perturbations under the influence of one, or several, applied magnetic fields. The reliable measurement of these very small field changes, and the involved mathematics to solve the inverse problem, are the main challenges for this flow diagnostic method. We present preliminary results of CIFT applied to a thermally driven flow within a setup showing some similarity to Czochralski silicon crystal growth. As working fluid GaInSn was used. Due to the low velocities in the order of 1 cm/s, the dynamic range of the measurement system has to be enhanced to 5 orders of magnitude which set high demands on the stability of the installation and the current source. Large efforts were made to adapt CIFT to the experimental setup in order to compensate thermal expansion during the measurement. Typical features of the thermally driven turbulent flow could be detected in the magnetic field measurements and were verified by simultaneous temperature measurements recorded by thermocouples placed in the vicinity of the rim of the heat sink.

Electromagnetic induction (EMI) is known as a technique which is very sensitive to variation of electrical conductivity of materials. In the present study we simulate numerically the work of electromagnetic sensor which consists of two differential coils. Such a detector rejects the basic signal and monitors the perturbations of electromagnetic field caused by the heterogeneity of electrical conductivity. We investigate the capability of this method for detecting non-metallic inclusions, such as gas bubbles in liquid metal (GaInSn) and sensitivity of differential detector to variation of its configuration.

Model experiments with low melting point liquid metals are an important tool to investigate the flow structure and related transport processes in melt flows relevant for metallurgical applications. We present recent results from the three LIMMCAST facilities working either with room-temperature alloy GaInSn or with the alloy SnBi at temperatures of 200-350°C. The main value of cold metal laboratory experiments consists in the capabilities to obtain quantitative flow measurements with a reasonable spatial and temporal resolution, which is essential for code validation. Experimental results are presented covering the following phenomena: contactless electromagnetic tomography of the flow in the mold, flow monitoring by ultrasonic sensors, mold flow under the influence of an electromagnetic brake, injection of argon bubbles through the stopper rod, X-ray visualization of gas bubble two-phase flow in the nozzle and in the mold.

Electromagnetic induction (EMI) is known as a technique which is very sensitive to variation of electrical conductivity of materials. In this paper, we investigate capability of this method for detecting non-metallic inclusions, such as gas bubbles in liquid metal (GaInSn). We make both numerical simulation and experiment in order to build the sensitivity map for the interior of a rectangular column filled with liquid metal. The electromagnetic sensor consists of two differential coils. Such a detector rejects the basic signal and monitors the perturbations of electromagnetic field caused by heterogeneity of electrical conductivity. Theoretical results are used for validation of measured signals. The method is capable of detecting spherical target we used instead of real gas bubbles and produce a good agreement with numerical data.

The AC electromagnetic induction is the most appropriate mechanism for monitoring of metallic objects and media with inhomogeneous distribution of electrical conductivity. In particular, the liquid metal flows with gas bubbles inside can be controlled by this method. In the present work we show a particular case when the series of 1D measurements can be applied for definition of position of a single gas bubble in y and z directions. The numerical experiment was made within a rectangular column filled with the liquid metal as it is shown in Figure (a). The basic AC (100 Hz) magnetic field was generated by a rectangular excitation coil. Typical distribution of the amplitude value of secondary magnetic field caused by a single bubble (5 mm) is shown in Fig.(c). The wall of measurement is opposite to the excitation coil. The shown normal component of magnetic field can generate an electrical signal in a measuring coil applied to the wall. In our experiment we use a system of rectangular coils stretched in horizontal and vertical directions (Fig. a,c). A detector of such configuration averages the value of magnetic field flux within the long direction of the coil. Vice versa, a number of detectors can give the detailed information about distribution of magnetic field along the short sides of the coils. So far as the secondary magnetic field is presented by a dipolar structure (Fig. c) where the central singular point corresponds to position of the bubble, the signal collected from the series of coils has a zero point situated between two extremes (Fig. b, c). This zero point indicates position of the bubble. Thus, using a system of vertical and horizontal coils placed on the rear walls (Fig. a,c), one can estimate position of a single bubble in y and z directions according to two 1D distributions of the signal. In our numerical experiment a single bubble moves in vertical direction by a spiral trajectory (Fig. d). In Figure (e) we reconstruct the y and z coordinates of the bubble (red circles). The real positions of the bubble are marked by the small blue circles in this figure.

Local velocity measurement of liquid metals continues to be an unsolved issue. Contact or even contactless measurement techniques cannot be used due to the fact that metal melts, like liquid steel, are usually at high temperatures, aggressive and opaque. Fortunately, there is a contactless velocity measurement technique called Lorentz force velocimetry in which a static magnetic field is applied on the electrically conductive metal stream. This static magnetic field is produced by permanent magnets, and if their size is smaller in comparison with the cross-section of the flow, a localized magnetic field distribution on the liquid metal is achieved. As a result and according to the principles of magnetohydrodynamics, eddy currents are generated within the liquid giving rise to a localized flow-breaking Lorentz force. Additionally and owing to Newtons third law, a force of the same magnitude but in the streamwise direction acts on the permanent magnet system which is connected to an optical interference force measurement device, giving access to local velocity information. This paper presents the results of local Lorentz force velocimetry at the mini-Limmcast facility at Helmholtz-Zentrum Dresden - Rosendorf using a 10mm cubic magnet and having as test fluid Galinstan in eutectic composition. In addition, partial results of Lorentz LFV using a multi-degree-of-freedom force/torque sensor are presented.

The Contactless Inductive Flow Tomography (CIFT) allows the reconstruction of the mean three dimensional flow structure in conducting liquids [1]. Exposing the liquid to one or multiple applied magnetic fields and measuring the flow induced magnetic field around the fluid volume, it is possible to infer the velocity field by solving a linear inverse problem with appropriate regularization techniques. One challenge is the reliable detection of the tiny flow induced perturbation of the applied magnetic field. Typically, the flow induced magnetic field is about 3 to 5 orders of magnitude smaller than the applied magnetic field, so that a measurement system with a high dynamic range is required. We start with a short overview of the first demonstration experiment of CIFT [1]. In a cylindrical vessel filled with GaInSn a propeller generates a three dimensional flow structure with a maximum velocity of 1 m/s. The flow induced magnetic field is about 3 orders of magnitude smaller than the applied magnetic field. One promising application for CIFT is the continuous casting of steel in which the flow structure in the mould is very important for the quality of the produced steel. For a model of a continuous slab caster operated with GaInSn we developed a measurement system consisting of one excitation coil around the mould and 14 magnetic field sensors [2]. In this industrially relevant setup the flow induced magnetic field is about 4 orders of magnitude smaller than the applied magnetic field. We were able to reconstruct different flow transitions in the mould in case that Argon was injected into the submerged entry nozzle (SEN) [3], and various effects of an electromagnetic stirrer at the SEN on the flow in the mould [3]. Recent developments concerned the reconstruction of the flow in the mould in the presence of a strong static magnetic field. Additionally, we show preliminary measurements at a modified Rayleigh-Bénard setup operated with GaInSn demonstrating the applicability of CIFT for thermally driven convection systems with velocities in the order of 0.01 m/s. Typical features of the thermally driven turbulent flow could be detected in the magnetic field measurements and were verified by simultaneous temperature measurements recorded by small thermocouples. References 1. F. Stefani et al., Physical Review E, 70 (2004), 056306 2. T. Wondrak et al., Measurement Science & Technology 21 (2010), 045402 3. T. Wondrak et al., Metallurgical and Materials Transactions B 42 (2011), 1201-1210

Most of the steel in the world is produced by continuous casting, where liquid metal flows from a tundish through a submerged entry nozzle into a copper mould. The mould is cooled by water, so a solid shell starts to form at the mould walls. The resulting steel strand is pulled out of the mould continuously and solidifies completely. In industry it is well-known that an unstable flow in the mould has negative effects on the resulting steel’s quality. Electromagnetic brakes (EMBr) are expected to dampen instabilities, although their impact on the flow can hardly be examined directly in liquid steel. In spite of the casting method’s economical and industrial importance, only a few simple measurement techniques are available to investigate the actual flow patterns in the mould. A more sophisticated technique for liquid metal flow measurements could help to resolve the open issues in the mould flow. The contactless inductive flow tomography (CIFT) is a technique that measures the mean global flow of an electrically conducting melt by exposing it to a magnetic excitation field and measuring the flow induced perturbations of that field outside the melt. The velocity profile can then be calculated by solving an inverse problem, using adequate regularization techniques to deal with the non-uniqueness. We present preliminary results for a physical model of a mould with a rectangular cross-section of 140 × 35 mm 2 in the presence of an EMBr. Additionally we show flow reconstructions for a 400 × 100 mm 2 mould, demonstrating the upward scalability of CIFT.

The flow structure of liquid steel in the mold of a continuous caster has huge impact on the quality of the produced steel. In order to influence the flow during the casting process electromagnetic brakes (EMBr) are used. Even a rough knowledge of the flow field would be highly desirable. The contactless inductive flow tomography is a technique for reconstructing the velocity field in electrically conducting melts from externally measured induced magnetic fields. For a physical model of a mold with a cross section of 140 mm × 35 mm we present preliminary measurements of the flow field in the mold in the presence of a magnetic brake. In addition, we show first reconstructions of the flow field in a mold with the cross section of 400 mm × 100 mm, demonstrating the upward scalability of CIFT.

The detection of bubbles in liquid metals is important for many technical applications like for continuous casting and for liquid metal cooled reactors. The opaqueness and the high temperature of liquid metals set high demands on the measurement system. Exploiting the high electrical conductivity contactless electromagnetic methods can be used. For instance, Mutual Inductance Tomography is able to visualize the distribution of gas and liquid metal in one cross section of a pipe using a sensor array of 8 induction coils.

Die Strömung der Metallschmalze beim kontinuierlichen Stranggießen hat wesentlichen Einfluss auf das erreichte Gussergebnis. Probleme entstehen beispielsweise durch Einschlüsse von Oxiden, intermetallischen Verbindungen oder Gasblasen, die durch eine unkontrollierte Strömung in die Erstarrungszone gelangen. Die Untersuchung und Optimierung der Strömungsvorgänge erfolgte bisher vorwiegend anhand von numerischen Simulationen sowie Wassermodellen und lieferte bereits viele Erkenntnisse. Aufgrund der Materialeigenschaften sind jedoch Wassermodelle in ihrer Anwendung begrenzt und können nicht alle im Prozess auftretende physikalische Phänomene abdecken, wie z.B. Temperaturgradienten in der Schmelze, Interaktion mit elektromagnetischen Feldern oder Mehrphasenströmungen. In diesen Fällen unterscheiden sich die Kennzahlen z.T. um mehrere Größenordnungen. Am Helmholtz-Zentrum Dresden-Rossendorf stehen drei Anlagen zur Verfügung, welche sich mit der Modellierung des Stranggussprozesses unter der Verwendung niedrigschmelzender Legierungen befassen. Die Anlagen unterscheiden sich z.T. in der Ausrichtung ihrer Untersuchungsschwerpunkte und ergänzen sich so gegenseitig ideal. Das Mini-LIMMCAST Experiment arbeitet mit einer bei Raumtemperatur flüssigen Legierung und ist sehr flexibel aufgebaut. Viele unterschiedliche Untersuchungen können und sind hier bereits durchgeführt worden. Die große LIMMCAST-Anlage ist insbesondere für einen längeren kontinuierlichen Betrieb ausgelegt und operiert im Temperaturbereich von 200 – 350 °C. Die dritte Anlage X-LIMMCAST ist speziell für die Röntgenbildgebung und die Visualisierung der Zweiphasenströmung mit Gasblasen konzipiert. Die Flexibilität der Anlagen erlaubt eine Anpassung an konkrete Gegebenheiten. Neben den experimentellen Anlagen müssen für einen sinnvollen Betrieb auch entsprechende Messtechniken zu Erfassung der Strömungsvorgänge in flüssigen Metallen zur Verfügung stehen. Für die Geschwindigkeitsmessung sind dazu in den Versuchen die Ultraschall-Doppler-Velocimetry, die kontaktlose, induktive Strömungstomographie und die Potentialsondenmethode zum Einsatz gekommen. Für die Auflösung der Zweiphasenströmung sind wiederum eine tomographische Methode als auch die Röntgenbildgebung verwendet worden. Ziel ist neben einem tieferen Verständnis des Prozesses, die Bereitstellung eine breiteren Datenbasis für die Validierung numerischer Modelle. Es sollen in diesem Beitrag die drei Versuchsanlagen und ausgewählte Messtechniken beispielhaft anhand von Messergebnissen vorgestellt werden.

The detection of bubbles in liquid metals flow is important for many technical applications. The opaqueness and the high temperature of liquid metals set high demands on the measurement system. The electrical conductivity of the liquid metal is relatively high, which can be exploited with contactless methods based on electromagnetic induction. We will present a measurement system which consists of one transmitting coil and a planar gradiometric coil on opposite sides of the pipe. With this sensor we were able to detect bubbles in a Sodium flow inside a stainless steel pipe.

Den Strömungszustand von Metall- oder Halbleiterschmelzen auch nur ungefähr zu kennen, wäre bei vielen technischen Anwendungen, wie z. B. beim kontinuierlichen Stranggießen von Stahl oder bei verschiedenen Kristallzüchtungsverfahren in der Halbleiterindustrie, von großem Wert. Die Messung der Strömung stellt aufgrund der hohen Temperaturen von oft mehr als 1000 ◦ C und aufgrund der Intransparenz der Schmelzen besonders hohe Anforderungen an die Messtechnik. Am Helmholtz-Zentrum Dresden-Rossendorf (HZDR) wurde ein auf der Induktion in bewegten Leitern basierendes kontaktloses Messverfahren, die kontaktlose induktive Strömungstomographie (contactless inductive flow tomography (CIFT)), entwickelt, die aus der Messung der durch die Strömung verzerrten angelegten Magnetfelder ein dreidimensionales Geschwindigkeitsfeld in der Schmelze rekonstruiert. In der vorliegenden Arbeit wird untersucht, ob sich CIFT auch bei industriell relevanten Anwendungen wie beim kontinuierlichen Stranggießen oder beim Ziehen von monokristallinen Siliziumkristallen einsetzen lässt. Dazu wurde CIFT für ein Modell einer Stranggießanlage adaptiert und ein Messsystem mit 14 Magnetfeldsensoren entwickelt, das es ermöglicht die dominierende zweidimensionale Strömung in der Kokille für das Brammengießen mit einer zeitlichen Auflösung von 1 Hz zu rekonstruieren. In einer Versuchsreihe mit einer Zweiphasenströmung konnten bei hohen Gasdurchflüssen Übergänge zwischen unterschiedlichen Strömungsregimen visualisiert werden. Begleitende Ultraschall-Doppler Geschwindigkeitsmessungen wurden für die Validierung der von CIFT rekonstruierten Geschwindigkeitsverteilung herangezogen. Für die Anwendung von CIFT in einer industriell relevanten Umgebung wurde CIFT dahingehend erweitert, dass Gradientensonden, ein Wechselfeld als Messfeld und Tiegel mit leitfähigen Wänden eingesetzt werden können. Ein weiterer Schwerpunkt dieser Arbeit waren erste Magnetfeldmessungen für CIFT an einer in der Industrie eingesetzten Czochralski-Ziehanlage. Dabei konnte gezeigt werden, dass trotz des großen Abstands zwischen Tiegel und Magnetfeldsensor das durch die Strömung induzierte Magnetfeld außerhalb der Anlage detektierbar ist. Diese Arbeit belegt, dass trotz der typischerweise sehr kleinen zu messenden induzierten Magnetfelder CIFT ein großes Potential für den Einsatz in industriell relevanten Anwendungen hat, insbesondere für die permanente Überwachung der Strömungsverhältnisse im Stahlguss.

In order to examine the flow structure in a continuous casting mold which is important for the quality of the produced steel, at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) three different models of a continuous caster are available to study the flow in a continuous casting mold. Those cold liquid metal models which use metallic alloys with low melting point e.g. up to 200 °C offer the application of different measurement techniques like ultrasound doppler velocimetry, x-ray and potential probes for flow investigation. Second, these models can be used to study the influence of magnetic actuators to the flow due to their high conductivity, contrary to water models. Third, these models can be used to develop new measurement techniques which can be applied in a real caster. We will give a short overview of the measurement techniques available for those models. Additionally we will present the newly developed Contactless Inductive Flow Tomography which can reconstruct the flow in the mold by measuring the flow induced perturbation of an applied magnetic field. This technique has the ability to be deployed in a real caster.

We present preliminary results of flow measurements for two different models of continuous casters using the contactless inductive flow tomography. In the first experiment we used a rectangular slab caster with a dominating two-dimensional flow structure under the influence of an electromagnetic brake. For the second experiment a round caster was used in which a magnetic stirrer around the submerged entry nozzle should create an unstable three-dimensional swirling flow.

Model experiments with low melting point liquid metals are an important tool to investigate the flow structure and related transport processes in melt flows relevant for metallurgical applications. We present the experimental facility LIMMCAST for modelling the continuous casting process of steel using the alloy SnBi at temperatures of 200-400°C. The parameters of the facility and the dimensions of the test sections will be given, and the possibilities for flow investigations in tundish, submerged entry nozzle and mould will be discussed. In addition, the smaller set-ups mini-LIMMCAST and X-LIMMCAST will be presented, which work with the room-temperature liquid alloy GaInSn. The main value of cold metal laboratory experiments consists in the capabilities to obtain quantitative flow measurements with a reasonable spatial and temporal resolution. New ultrasonic and electromagnetic techniques for measuring the velocity in liquid metal flows came up during the last decade allowing for a satisfying characterisation of flow quantities in the considered temperature range up to 400°C. A selection of results will be presented in this paper covering various phenomena occurring in single-phase and two-phase flows.

In order to enhance the productivity and to achieve higher steel cleanliness in continuous casting the application of various magnetic fields is considered an efficient tool for controlling the flow in the mold. For instance, DC magnetic fields perpendicular to the wide faces of the mold are used to dampen the jets emerging from the submerged entry nozzle (SEN). Especially in this case, even a rough knowledge of the flow structure in the mold would be highly desirable. The Contactless Inductive Flow Tomography (CIFT) allows reconstructing the dominating two-dimensional flow structure in a slab casting mold by applying one external magnetic field and by measuring the flow induced magnetic fields along the narrow faces of the mold. For a physical model of a continuous caster, consisting of a mold with a cross section of 140 mm x 35 mm, we will present first measurements of the flow induced magnetic field in the presence of a magnetic brake of the ruler type. The first results demonstrate the viability of the CIFT measurement technique in such a configuration.

The Contactless Inductive Flow Tomography (CIFT) allows for determining flow structures in conducting liquids which are exposed to one or more external magnetic fields. Measuring the induced fields around the fluid volume for each of the applied fields, it is possible to infer the velocity field by solving an inverse problem with appropriate regularization techniques. We will give an overview of the CIFT method and present the measurement system for the model of a continuous caster at the HZDR. We will conclude with new developments towards a robust measurement of the very small induced magnetic fields.

We present a combined numerical and experimental investigation of an electromagnetic system dedicated for an operative detection of non-metallic enclosures (gas bubbles) into the liquid metal flows. The method is based on generation of eddy currents in the electrically conducting medium by applying of ac magnetic field and detection of the electromagnetic distortions caused by inhomogeneity of electrical conductivity of the medium. We defined an optimal position and configuration of detector in order to get maximal sensitivity of the system to the spatial distribution of admixture.

Liquid metal cooling or liquid metal targets belong to innovative reactor concepts such as fast reactor cooled by sodium or lead and the lead-bismuth target in a transmutation system. The safe and reliable operation of liquid metal systems requires corresponding measuring systems and control units, both for the liquid metal single-phase flow as well as for bubble-laden liquid metal two-phase flows. However, velocity measurements in opaque liquid metal flows still represent a challenging task as commercial measuring systems are not available for such fluids. During the last 15 years, considerable effort was spent at HZDR on the development and qualification of techniques to measure the velocity in metallic melts. Especially, significant progress has been achieved in the field of non-invasive measuring techniques. Recent reviews regarding the principles of different velocity measurement systems and their applicability have been published. In general, measurement techniques are needed to determine flow rates, flow velocities, heat fluxes, pressures, and free surface levels. Within this paper we present some new developments comprising electromagnetic flow meters, ultrasonic Doppler measurements and a contactless inductive flow tomography. The capabilities of these measuring techniques have been verified by tests at HZDR using various liquid metal loops operating with lead, LBE, SnBi or sodium.

Heiße Schmelzen werden in vielen Technologien eingesetzt, beginnend beim traditionellen Stahlguss über die Elektrolyse von Aluminium bis hin zur Züchtung von Silizium-Einkristallen. In der Optimierung dieser sehr energieintensiven Prozesse liegt ein volkswirtschaftlich relevantes Einsparpotenzial. Grundlage einer optimalen Prozessführung ist aber stets die Kenntnis der relevanten physikalischen Parameter der Schmelze, zu denen neben Temperatur, Druck und Lage der Phasengrenzen häufig auch das Geschwindigkeitsfeld gehört. Ein typisches Beispiel hierfür ist der Strangguss von Stahl, dessen finale Qualität ganz wesentlich von der Strömungsstruktur in der Kokille abhängt. Die online-Bestimmung dieser Strömung während des Gießprozesses würde die Möglichkeit einer aktiven Strömungskontrolle eröffnen, mit deren Hilfe deutlich höhere Gießgeschwindigkeiten erreicht werden könnten. In diesem Beitrag werden verschiedene Messprinzipien und ihre Anwendung für Flüssigmetallströmungen besprochen. Das erste Verfahren, die Ultraschall-Doppler-Velozimetrie (UDV), beruht auf der Bestimmung der Doppler-Frequenz-Verschiebung bei der Rückstreuung an bewegten Streuteilchen. Das zweite Verfahren nutzt den Faradayschen Induktionseffekt in bewegten elektrischen Leitern unter dem Einfluss eines äußeren Magnetfeldes. Auf dieser Basis wurden mehrerer kontaktlose Messverfahren entwickelt, so z.B. zur Bestimmung von Durchflüssen in Rohrströmungen, aber auch zur tomographischen Rekonstruktion vollständiger zwei- oder dreidimensionaler Geschwindigkeitsfelder.

Model experiments with low melting point liquid metals are an important tool to investigate the flow structure and related transport processes in melt flows relevant for metallurgical applications.We present the new experimental facility LIMMCAST for modelling the continuous casting process of steel using the alloy SnBi at temperatures of 200-400°C. The parameters of the facility and the dimensions of the test sections will be given, and the possibilities for flow investigations in tundish, submerged entry nozzle and mould will be discussed. In addition, the smaller set-up Mini-LIMMCAST will be presented, which works with the room-temperature liquid alloy GaInSn. The main value of cold metal laboratory experiments consists in the capabilities to obtain quantitative flow measurements with a reasonable spatial and temporal resolution. New ultrasonic and electromagnetic techniques for measuring the velocity in liquid metal flows came up during the last decade allowing for a satisfying characterisation of flow quantities in the considered temperature range up to 400°C. First results from LIMMCAST and Mini-LIMMCAST will be presented covering the following phenomena: fully contactless electromagnetic tomography of the flow in the mould, flow monitoring by a multitude of ultrasonic sensors, and analysis of the flow in the mould under the influence of an electromagnetic brake: intensification of the flow turbulence contrary to the expected flow damping, injection of argon bubbles through the stopper rod: occurrence of pressure oscillations.

The safe and reliable operation of liquid metal systems requires corresponding measuring systems and control units, both for the liquid metal single-phase flow as well as for bubble-laden liquid metal two-phase flows. However, velocity measurements in opaque liquid metal flows still represent a challenging task as commercial measuring systems are not available for such fluids. The paper reports on established methods and new developments in the field of measuring techniques for liquid metal flows. The presentation is focussed on measurements of the flow rate and the local velocity field as well as on the characterization of liquid metal two-phase flows. During the last two decades considerable effort was spent by miscellaneous researcher groups to provide new solutions for measurements of flow fields in liquid metals. This paper intends to summarize different approaches and tempts to account on perspectives, particularly in view of some recent developments (ultrasonic techniques, magnetic tomography).

This paper describes experimental investigations of flow structures and related transport processes in the continuous casting mould under the influence of an external DC magnetic field at laboratory scale. Experimental results will be presented here which have been obtained using a physical model (mini-LIMMCAST) operating with the low melting point alloy GaInSn. According to the concept of the electromagnetic brake the impact of a DC magnetic field on the outlet flow from the Submerged Entry Nozzle (SEN) has been studied up to Hartmann numbers of about 400. The Ultrasound-Doppler-Velocimetry (UDV) was applied for measurements of the flow pattern in the mould. Local conductivity anemometers were used to measure the turbulent quantities of the flow. The effect of the magnetic field on the flow structure turned out to be manifold and rather complex. The magnetic field causes a deflection of the jet, at which the respective exit angle from the nozzle ports becomes more flat. Thus, both the penetration depth of the discharging flow into the lower part of the mould and the impinging velocity of the jet onto the side wall are reduced. A significant return flow occurs in the adjacent regions of the jet. Specific vortices are formed with axes being aligned with the magnetic field direction. Such vortical structures are typical for quasi-two-dimensional magneto-hydrodynamic (MHD) flows. The flow measurements do not manifest a general braking effect which would be expected as an overall damping of the flow velocity and the related fluctuations all-over the mould volume. Variations of the wall conductivity showed a striking impact on the resulting flow structures.

The aim of the Contactless Inductive Flow Tomography (CIFT) is the reconstruction of flow structures in metal and semiconductor melts. It relies on the induction of electric currents in moving conductors exposed to magnetic fields. The flow induced deformations of various applied magnetic fields can be measured in the exterior of the melt and utilized for the reconstruction of the velocity field. After a presentation of the principles of CIFT, first applications and possible extensions of the method are discussed and put into the context with traditional measuring techniques such as UDV.

For a physical model of a continuous caster, we present results on the simultaneous measurements of the flow in the mould by the Contactless Inductive Flow Tomography (CIFT), and of the conductivity distribution in the submerged entry nozzle (SEN) by Mutual Inductance Tomography (MIT) for a two phase flow setup. Depending on the gas flow rate, various flow regimes in the SEN and in the mould are identified, among them pressure oscillations in the gas feeding system, transitions between double and single vortex flows, and transient single port ejections. In addition we give a summary of an experimental campaign with a magnetic stirrer around the SEN and its effects on the flow in the mould. As expected and desired, the swirling flow leads to a stronger upward fluid motion along the walls. At the same time, however, the oscillatory character of the flow becomes stronger. The paper concludes with some new developments for CIFT towards a robust measurement of the very small induced magnetic field using pickup coils which allow the application of CIFT in environments with high DC magnetic fields and strong noise.

The flow structure in the mould of a continuous caster is of key importance for the quality of the final product. The use of most conventional flow measurement techniques is prevented by the high temperature of the liquid steel. For a downscaled physical model of the continuous casting process, we present combined measurements of the flow in the mould by Contactless Inductive Flow Tomography (CIFT), and of the conductivity distribution in the submerged entry nozzle by Mutual Inductance Tomography (MIT). In addition, we summarize an experiment with a magnetic stirrer around the submerged entry nozzle and its effects on the flow in the mould. Some new developments towards a robust implementation of CIFT at a real caster, including the use of pickup coils and gradiometric probes, are also discussed.