Transient Eddy Current Flow Metering: calibration-free velocity measurements for liquid metals

Most inductive techniques for the velocity measurement of liquid metals have the common problem that the measured signals depend on the electrical conductivity and the temperature of the liquid metal. This is particularly unfavourable for applications with strong temperature fluctuations or for measurements that have to be performed in different liquid metals with the same sensor. Usually these sensors have to be calibrated extensively to ensure accurate measurement results. We present a new measurement technique called Transient Eddy Current Flow Metering (TECFM) which overcomes the need for prior calibration of the sensors. Its principle relies on imprinting transient eddy current systems into the liquid metal and to track their movement as they are advected with the flow. Two kinds of sensors that use this new measurement principle have been developed: An external sensor for the contactless velocity measurement at the boundary of liquid metal flows, and an immersed sensor which allows local velocity measurements in the vicinity of the sensor. Focusing on the latter we present the results of numerical simulations as well as the results of measurements that were performed in the eutectic alloy GaInSn at room temperature and in liquid sodium at 180 °C.