Magnetic Field Sources - Magnetocaloric Energy Conversion: From Theory to Applications - page 71

potential future market applications, have used permanent magnets. Superconduc-
ting magnets have been applied as well, although these were not constructed spe-
ci

cally for the application in magnetic refrigeration at room temperature (see also
the Chap. 7 ). Namely, researchers simply took advantage of existing supercon-
ducting magnets and since these solenoids consisted of a dewar vessel with a bore
for the magnetic eld in the middle, prototypes based on such solutions were linear

with the reciprocate movement of the magnetocaloric material (AMR) in and out of
the magnetic

eld. No special design of superconducting magnet for magnetic
refrigeration has been reported to date, despite the fact that this kind of technology
could bring (large-scale) market applications. This issue is addressed in the Chap. 9 .
In this section, however, we will focus on some of the design concepts that have
been used for permanent-magnet structures in magnetic refrigeration. More infor-
mation about particular devices can be found in the Chap. 8 .
We will divide the permanent-magnet designs into the following categories:

Static or moving simple (2D) magnet assemblies (which mostly relate to
different types of

￿

magnets).
These kinds of magnets are applied in linear or rotary machines in which the
magnetocaloric material is the rotating or linearly moving part, and where the
magnetic

“ horseshoe ”

eld source (magnet) is moved
linearly or rotated over the static magnetocaloric material in the form of an
AMR. The magnetic

eld source is static, or the magnetic

fl ux can be approximated to fl ow in two dimensions (2D).

Static Halbach (2D) magnet assemblies
These magnets are in an arrangement that was rst proposed by Halbach in 1980
[ 36 ]. Most of the prototypes that apply the (linear or rotary) motion of the
magnetocaloric material are based on such a solution. Figure 3.28 shows a basic
Halbach type of magnet assembly, consisting of a number of permanent mag-
nets, with the magnetization arranged in a such a way that the magnetic

￿

fl ux is

concentrated in the middle of the magnet assembly.

Rotary Halbach (2D) magnet assemblies
By taking the principle of a Halbach array, different approaches have been used
in order to perform a rotation of the magnet assembly or the rotation of a part of
the magnet assembly over the static magnetocaloric material. This kind
of principle, at least according to our knowledge and experiences, represents one

￿

Fig. 3.28 A typical Halbach
array of permanent magnets