Measuring techniques for experimental investigations and monitoring of liquid metal flows

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. Moreover, significant research effort is permanently focused on the optimization of technologies and facilities for materials processing such as smelting, refining and casting of metals and alloys. The main objectives are an improvement of the final product quality, an enhancement of the process efficiency and an economical consumption of resources and energy. Further developments of processes involving metallic melts require a better, detailed knowledge about the flow structure and the transport properties of the flow. Numerical simulations could provide a better understanding of the complex flow behavior, but, experimental data are indispensable with respect to a validation of the respective CFD codes. The determination of flow quantities in liquid metals is considerably impeded by the special material properties. Powerful optical methods as used for measurements in transparent liquids are obviously not applicable in molten metals. Further serious restrictions arise from the high temperature or the chemical reactivity of the melt. As a consequence there is a very constrained choice of commercially available techniques to measure the velocity structure of fluid flows at elevated temperatures.
The presentation reports on established methods and new developments in the field of measuring techniques for liquid metal flows. This review is focused on measurements of the flow rate and the local velocity field as well as on the characterization of liquid metal two-phase flows and solidifying melts. 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. The presentation intends to summarize different approaches and attempts to account on perspectives, particularly in view of some recent developments.