Experimental determination of turbulent flow characteristics,
temperature and electromagnetic force density fields
in the melt of induction furnaces

Dr.-Ing. Egbert Baake, Prof. Dr.-Ing. Dr. h.c. Alfred Mühlbauer

Institute for Electroheat, University of Hannover,
W.-Busch-Straße 4, D-30167 Hannover, Germany

The experimental determination of electromagnetic, hydrodynamic and thermal fields is indispensable for the evaluation of computer simulation results. Fore more than ten years the Institute for Electroheat, University of Hannover, has experience in the development and application of different measurement techniques for turbulent metal flows in induction furnaces. This paper describes the used measurement systems and presents various results along with selected examples of the determination of particular fluctuation rates and time averaged flow velocities, temperature and electromagnetic force density distributions in the melt of different induction furnaces, e.g. induction channel and induction crucible furnaces.

Wood´s metal, which has a melting point of 72°C is used as a model melt. The hydrodynamic studies are carried out using permanent magnetic sensors [1]. The velocity sensors are calibrated with a self developed rotating channel. Due to the detected decrease of the magnetization of the permanent magnets by the influence of temperature and strong alternating magnetic fields in the melt, a remagnetization of the permanent magnet sensors is necessary. Therefore a self constructed remagnetization device is used and the magnetization is checked using a Hall-sensor. The use of two types of sensors allows three-dimensional investigations. The fluctuation rates are measured with a scanning rate of 20 Hz in order to determine the characteristics of the turbulence: the turbulent kinetic energy, the dissipation rate and the turbulent viscosity. The autocorrelation analysis of the local flow velocity components in different zones in the melt of the induction furnaces are investigated and show low frequency fluctuations with different, position dependent oscillation frequencies in the range of lower than 10 Hz.

In addition to the mainly used Wood´s metal, local flow velocity measurements in the melt of Aluminium are carried out. Due to the high temperature level of 700°C, permanent magnet sensors are unsuitable. Therefore the velocity measurements in liquid aluminium are realized using a self developed electromagnetic sensor [2].

In parallel to the local flow velocities the temperature distribution in the melt is investigated using embedded thermocouples. By this way the correlation analysis between the local flow velocity and the local temperature fluctuations is carried out in order to analyse the heat and mass transfer in the melt.

The local current density and the magnetic flux density in the melt of induction furnaces are measured with a scanning rate of 10 kHz in order to determine the electromagnetic force density distribution. For this the phase angle between current density and magnetic flux density has to be defined by simultaneously measuring of the inductor current with a Rogowski belt.