S. Men, C. Resagk, H. Brauer, M. Ziolkowski, M. Kuilekov Ilmenau University of Technology 2D Measurements of Magnetic Field near the Interface between Two Fluids Carrying an Electrical Current

 Motivation  Theoretical Model  Experimental Setup  Results and Discussion  Summary and outlook Outline

Motivation Several MHD applications in processing of materials: Aluminum reduction, steel/iron making, glass melting, crystal growth, etc. require deep knowledge of behaviors of the surface/interface of electrically conducting fluids. the use of probes is difficult or even impossible (limited access and hostile environment). necessary to develop appropriate methods for cell diagnosis.

Build up a magnetic sensor system to detect weak magnetic field (~nT); Develop optical techniques to observe interface displacement; Identify the main interface shape features by means of MFT. Magnetic Field Tomography (MFT) Construct a highly simplified aluminium reduction cell to investigate a MFT system

Theoretical Model

Experimental Setup CCD camera Light sheet laser Two-fluid cell: KOH+ GaInSn Pneumatic shaker

Specifications: Measuring range: ±100µT Output voltage: ±18.5mV/µT Noise:  30pT/  Hz Bandwidth(-3dB): DC to 1.25kHz Linearity:  0.25% Orthogonality:  1° Operating temp: -40~+85°C Zero drift:  100nT/K Supply voltage: 5V ±0.1V DC Supply current:  5mA eff Output impedance: <1k  Dimensions— sensor:  2mm  15mm electronics: 26mm 2D fluxgate sensor -FXM 205

Optical measurement of interface oscillation Results and discussion Mode 11 : f shaker = Hz f shaker =7.3Hz, I dc =1.0A, A=10.17mm Mode 21 : f shaker = Hz f shaker =9.4Hz, I dc =1.0A, A=8.28mm

electrolyte   liquid metal   BzBzBzBz BrBrBrBr J0J0J0J0 Simulation of interface oscillation mode 11, A=10mm

Simulation of interface oscillation mode 21, A=8.0mm

Schematic of data acquisition and processing

Signals of eight B z and B r at f shaker =7.3Hz, z=57.5mm Magnetic field measurements Peak at 3.65Hz  Subharmonic at interface

Contour line of mode 11 at 1.0A, f shaker =7.3Hz Forward calculationMeasurements BzBz BzBz BrBr BrBr A= mm A=10.0mm

Mode 21 at f shaker =9.4Hz, I dc =1.0A Forward calculation Measurement A= mm A=8.0mm

Interface mode  mn, A FEM3D Extract current density Biot-Savart law Magnetid flux density In sensor positions Flow chart of interface reconstruction

Reconstructed interface CF  12% CF  16% mode 21mode

1.A sensor ring consisting of eight 2D sensors is suitable to measure the magnetic field near the oscillating interface between two electrically conducting fluids for modes m  2, n  3. 2.Forward calculation by FEM3D based on the optical measurement is consistent well with the experimental results. 3.Evolutionary algorithm is effective for the magnetic field tomography to reconstruct a non-axisymmetric interface of a low mode. 4.Better experimental results (smaller reconstruction error) can be expected when more sensors in one ring and/or more sensor rings are applied. 5.A rectangular cell whose shape is similar to an aluminium reduction cell will be investigated a little later. Summary and outlook

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