Measuring Techniques for Liquid Metals

The techniques of local and instantaneous measurements in liquid metals are known to be much more difficult than in classical fluids like water and air. Whatever diagnostic method is used, two categories of problems have to be solved: those due to the nature of the fluid (opaqueness, high temperatures or chemical reactions) and in addition due to the presence of a magnetic field if MHD flows should be examined. Almost all conventional measuring techniques used for ordinary flows fail in liquid metal MHD flows totally or their applicability is strongly limited. The use of local sensors inside the liquid metal requires materials being robust against the attack of the fluid.

The development of a new mechano-optical technique to determine the local velocity in non-transparent fluids is one of the topics in frame of the DFG-Innovationskolleg "Magnetohydrodynamics of Electrically Conducting Fluids". Moreover, in our group experiences exist to adapt measuring principles being well-known from ordinary hydrodynamics to liquid metal applications. Thus, void fraction measurements by means of electrical resistive probes have been performed successfully in sodium, mercury and InGaSn two-phase flows. Another subject is to extend the field of application for US-Doppler Velocimetry developed at the Paul Scherrer Institute (PSI,Switzerland) to liquid metals at higher temperatures.

The following measuring techniques have been employed in our laboratory:

• Mechano-optical Sensor (velocity)
• Potential Probe or Conductance Anemometer (velocity)
• US-Doppler Velocimetry (velocity)
• Resistive Probes (void fraction)

In a close collaboration with the Forschungszentrum Jülich a X-ray screening technology has been used to observe directly the formation of bubbles in mercury and InGaSn, respectively.

European Project HITUV