Contactless inductive flow tomography: principles and applications


Contactless inductive flow tomography: principles and applications

Wondrak, T.; Stefani, F.; Gerbeth, G.; Gundrum, T.

There is a growing interest in the determination of the velocity field of metal or semiconductor melts in many industrial applications, such as steel casting and silicon growth. Due to the opaqueness of those fluids optical methods are not applicable. Furthermore these fluids are often very hot or chemically aggressive, so a contactless measuring technique would be highly desirable. Interestingly, those metal and semiconductor melts are characterized by a relatively high electrical conductivity. Exposing the flow of such melts to an externally applied magnetic field, electrical currents are induced which give rise to a perturbation of the applied field. This flow induced field perturbation, which is detectable outside the fluid volume, contains information about the flow structure and can be exploited to reconstruct the velocity field. By applying consecutively the external magnetic field in different directions, different induced currents and magnetic fields can be produced from the same velocity. This enables a tomographic reconstruction of the flow field. Such a contactless inductive flow tomography (CIFT) was proposed, and later verified experimentally. The determination of the velocity from the measured induced magnetic field is an ill-posed linear inverse problem. One of the key problems is the inherent non-uniqueness of the reconstruction. For the velocity reconstruction we circumvent this non-uniqueness problem by using Tikhonov regularization and the method of the L-curve to identify automatically the best regularization parameter. At the point of strongest curvature (the knee) of the L-curve one expects the most reasonable compromise between the fit of the modeled magnetic fields to the measured ones on one hand, and the minimum kinetic energy on the other hand. One possible application of CIFT is the continuous casting process which is widely used in the steel producing industry. The flow structure in the mould, where the steel starts to solidify, is of particular interest since it is mainly responsible for the quality of the produced steel slabs. Since for thin slab casting the velocity can be assumed to be mainly two-dimensional it is sufficient to apply only one external field. We show that the CIFT method is able to reconstruct a numerically determined flow field with an empirical correlation coefficient of about 75 per cent. Then we apply the method to different flow configurations in a real model and show that typical flow features can be reliably detected.

Keywords: velocity measurement; liquid metals; continuous casting; inverse problems

  • Lecture (Conference)
    5th International Conference: Inverse Problems: Modeling and Simulation, 24.-29.05.2010, Antalya, Türkei

Permalink: https://www.hzdr.de/publications/Publ-14637
Publ.-Id: 14637