O-26: Assembling and Test of a Halbach Array Magnet

O-26: Assembling and Test of a Halbach Array Magnet
System for Lorentz Force Velocimetry in Electrolytes
Part B3 („Electrolytes“) of the Research Training Group „Lorentz Force Velocimetry and Eddy Current Testing“ (GRK-1567) funded by the DFG
LFV: Background
M. Werner* and B. Halbedel
LFV:
Novel „contactless“ measurement method in electrolytes to provide
an in-line observation system for glass melts
Vision :
Improvement of the process efficiency in electrolytic processes (e.g.
glass casting, salt melt cooling) by measuring the flow velocities in
closed channels
Research: - Experiments on salt water under laboratory conditions with high
velocities (~ 5 m/s)
- Later adaption and optimization to a robust system for the harsh
boundary conditions of real glass melts at lower velocities
Challenge: Tiny forces (some µN) on magnet systems with masses around
1 kg must be detected with highest possible resolution
Task:
Michael Faraday
Georg Simon Ohm
Heinrich Friedrich Emil Lenz
Hendrik Antoon Lorentz
Isaac Newton
Channel
Primary magnetic
field
Fluid
Eddy currents
Fluid breaking
force
Accelerating
force
Flow
Magnet
- Finding the most effective magnet system design
- Optimization of the specific geometries of this magnet system
for highest forces within the limited mass, to increase load
step amount on force measurement system
- Assembling and characterization of the optimized design
- High Reynolds number (salt water at 5 m/s)
- Low magnetic Reynolds number
- Low Hartmann number and interaction
parameter
- Well defined test channel with plug profile
at the inlet
FEM simulation of moving solid bodies,
having the same geometry like the channel
cross section is possible in a first
approximation
- Inner cross section: a * b = 50 mm * 50 mm
- Length: lB = 1500 mm
- Conductivity of the fluid: σ = 4 S/m
- Flow velocity: v = 5 m/s
- Minimum gap between poles: δ > 56 mm
- Geometries of magnet system (here standard
system): l, d, h optimization parameters
- Magnet system mass limit: m < 1 kg
FEM
(Nelder-Mead simplex algorithm in MATLAB)
Optimization can be performed in very short
time by combination of COMSOL FEM and
MATLAB Optimization Toolbox
Standard system
Halbach array combination
(two single magnets with same
magnetization direction):
m = 950 g leads to Fmax = 35 µN with
lopt = 38.4 mm, hopt = 51.9 mm,
dopt = 31.8 mm
(without/with triangular shaped endmagnets) m = 950 g, Fmax = 115 µN)
34
32
30
28
40
Force [μN]
Optimization results
Optimization procedure
Reference design / experimental setup:
26
30
24
20
22
80
10
30
20
70
40
18
60
50
50
60
16
40
70
14
30
length l [mm]
80 20
height h [mm]
Lorentz force can be increased by a factor of three, using Mallinsons method of one sided
fluxes (1973) in the same way Halbach did in his arrays (1980).
Numerical investigation of the influence of the fluid profiles on the arising
Halbach array system out of 5 single magnets on each side,
assembled with a carbon fiber composite bracket. (950 g magnets forces by FLUENT simulation of the experimental test channel:
Force decreases with fluid profile change within the channel.
and 50 g CFC)
Magnetic field was measured and fits perfect to the numerical
predictions.
150
Magnetic field magnitude in y [mT]
Result and Outlook
Principle and Response surface for 950 g
magnet material (NdFeB of grade N52)
100
150
100
50
50
0
-50
0
-100
-150
40
-50
20
-20
0
0
-20
20
-40
-60
-100
Length l [mm] / x-direction
Height h [mm] / z-direction
Authors:
Dipl.-Ing. Michael Werner
Department of Inorganic-Nonmetallic Materials
Mail: [email protected]
Phone: +49 3677 69 3347
Dr.-Ing. Bernd Halbedel
Department of Inorganic-Nonmetallic Materials
Mail: [email protected]
Phone: +49 3677 69 2784
Next step:
- Further experimental
tests on the channel
to prove all
simulations, see also
Poster P3-19
- Design of magnet
systems based on
high temperature
superconductors