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

MotivationSeveral 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

M

Mm

N

nmnmmn mrkJAr

1

cos,

V

o Vdrr

rrrJrB 34

Experimental Setup

CCD camera

Lightsheet laser

Two-fluid cell:KOH+GaInSn

Pneumaticshaker

Specifications:Measuring range: ±100µTOutput voltage: ±18.5mV/µTNoise: 30pT/HzBandwidth(-3dB): DC to 1.25kHzLinearity: 0.25%Orthogonality: 1°Operating temp: -40~+85°CZero drift: 100nT/KSupply voltage: 5V ±0.1V DCSupply current: 5mA effOutput impedance: <1kDimensions— sensor: 2mm15mm electronics: 26mm

2D fluxgate sensor-FXM 205

Optical measurement of interface oscillation

Results and discussion

Mode 11 : fshaker=7.2-7.6Hz

fshaker=7.3Hz, Idc=1.0A, A=10.17mm

Mode 21 : fshaker=9.3-9.6Hz

fshaker=9.4Hz, Idc=1.0A, A=8.28mm

electrolyteelectrolyte

liquid metalliquid metal

BBzz

BBrr

JJ00

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 Bz and Br at fshaker=7.3Hz, z=57.5mm

Magnetic field measurements

Peak at 3.65Hz Subharmonic at interface

Contour line of mode 11 at 1.0A, fshaker=7.3Hz

Forward calculationMeasurements

Bz Bz

Br Br

A=9.5-10.5mm A=10.0mm

Mode 21 at fshaker=9.4Hz, Idc=1.0A

Forward calculationMeasurement

A=7.5-8.5mm A=8.0mm

Interface modemn, A

FEM3DExtract current

density

Biot-Savartlaw

Magnetid flux densityIn sensor positions

Flow chart of interface reconstruction

Reconstructed interface

CF12% CF 16%

mode 21mode 11

%100

1

22

1

22

Nsensor

i

measri

measzi

Nsensor

i

measriri

measzizi

BB

BBBBCF

10

-10

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 m2, n3.

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

Thank you for your attention!