Active Magnetic Regeneration - Magnetocaloric Energy Conversion: From Theory to Applications - page 107

4.2 Layered AMR

In the Fig. 4.11 , an AMR with layered magnetocaloric materials is shown. Why
layering of magnetocaloric materials is important?
One of the disadvantages of the known magnetocaloric materials (especially
those with a rst-order phase transition) is the relatively narrow temperature range

over which the magnetocaloric effect occurs (see Chap. 2 for details).
This is especially important when the magnetocaloric material is used in an
AMR and/or when large temperature spans between the heat source and heat sink
are required.
Since during the operation of the AMR a temperature pro le is established along

the length of the magnetocaloric material, this implies that according to the tem-
perature pro

le, some parts of the magnetocaloric material can be, temperature-
wise, relatively far from the material s Curie temperature. The magnetocaloric effect

for this part of the magnetocaloric material is therefore smaller compared to the
parts that are closer to the Curie temperature.
It has been shown experimentally and numerically in various studies [ 20

'

32 ]
that layering magnetocaloric materials with different Curie temperatures along the
AMR (in the

-

s performance (see
Fig. 4.11 a) due to the larger average magnetocaloric effect along its length.
The layering of magnetocaloric materials along the length of the AMR is
especially important when one applies

fl uid fl ow direction) increases the AMR '

rst-order phase transition materials (e.g.,

Mn Si), since their magnetocaloric effect is limited to a narrower

temperature range compared to the second-order phase transition materials like Gd.

Fe P; La Fe

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Fig. 4.11 a Example of a AMR with seven layers. b The magnetocaloric effect (magnetic entropy
change) of La Si with different Curie temperatures (reproduced from data obtained from

Vacuumschmelze GmbH)

Fe Co

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