Measuring techniques for liquid metal velocity measurements


Measuring techniques for liquid metal velocity measurements

Eckert, S.; Gerbeth, G.; Stefani, F.; Witke, W.

A better understanding and optimisation of liquid metal processes requires experimental data of the velocity field. Numerical simulations alone are often of limited value. To measure local velocities in liquid metals or to measure channel flow rates in a contact-less way, almost nothing is available commercially.
We report on various measuring technique developments, their test in different liquid metals, and applications in hot melts. For local velocity measurements, a mechano-optical probe working up to temperatures of about 800°C has been developed [1]. It delivers the two mean velocity components perpendicular to the sensor axis. In the presence of an external steady magnetic field, the use of local potential probes allows to analyse the turbulent properties of the flow in addition to the mean velocity [2]. However, both sensor techniques rely on the introduction of probes into the melt and are thus mainly of interest for laboratory purposes.
The Ultrasound Doppler Velocimetry (UDV) became a powerful tool to measure the velocity structure of liquid flows. Because of the ability to work in opaque fluids and to deliver complete velocity profiles in real time it is very attractive for liquid metal applications. In addition, it can principally operate through the channel wall though a direct contact to the melt reduces ultrasonic losses. However, in case of hot metallic melts the user is confronted with several problems: the application of the ultrasonic transducers is usually restricted to maximum temperatures of 200°C, and a good acoustic coupling between the liquid metal and the related interfaces has to be provided. We report on successful measurements in liquid sodium at 150°C [3] which were performed through the channel wall. To overcome the limitation of ultrasonic transducers to temperatures lower than 200°C, an integrated ultrasonic sensor with acoustic wave-guide has been developed. This sensor can presently be applied at maximum temperatures up to 1000°C. Stable and robust velocity measurements have been performed in various PbBi flows at about 250-300°C. We report on first successful measurements in a CuSn melt of about 620°C and in an Al melt of about 750°C.
Evidently, a fully contact-less measuring technique would be most desirable. Such a method has been developed making use of external magnetic field measurements and inverse reconstruction techniques [4]. We will report on a first demonstration experiment showing the feasibility of this approach for the reconstruction of the three-dimensional mean velocity structure.
For the flow rate measurement in a pipe, a contact-less solution based on a pair of alternating magnetic field transmitter and receiver has been developed. Test results from a laboratory model and an industrial Al casting process will be presented.

  • Lecture (Conference)
    Int. Symposium on liquid metal processing and casting, Nancy (France), Sept. 21-24, 2003. Proceedings, Eds.: P.D.Lee, A.Mitchell, J.-P.Bellot, A.Jardy, 261-271, 2003.
  • Contribution to proceedings
    Int. Symposium on liquid metal processing and casting, Nancy (France), Sept. 21-24, 2003. Proceedings, Eds.: P.D.Lee, A.Mitchell, J.-P.Bellot, A.Jardy, 261-271, 2003.

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Publ.-Id: 5399