GADOLINIUM is one of the more obscure
rare-earth elements. But it has a strange
property that could prove useful: when
put into a magnetic field, it heats up;
when demagnetised, it cools down.
Researchers at the Iowa State University
in the us are using this effect to create a
new principle in refrigerators by cooling
them with magnets.
Most modern refrigerators function
by circulating a fluid with a low boiling
point through the freezer. Evaporation
requires heat, and this heat is drawn in
from the surroundings. By pumping the
fluid into a freezer in such a way that it
expands and evaporates, heat is 'sucked'
out of the compartment. Condensation
from vapour to liquid liberates heat. In a
conventional refrigerator, condensation
takes places in an external radiator,
letting the heat from the fridge out into
The new fridge also utilises a
circulating fluid - water with a little
antifreeze added. The cooling is done
not by the expansion and compression
of the fluid, but by the magnetisation
and dernagnetisation of gadolinium.
Two cylindrical 'beds' containing small
gadolinium spheres are pushed out into
the magnetic field in opposition to one
another. As a bed enters the magnetic
field, it heats up. The heat generated is
allowed to dissipate into the environ-
ment and the bed is then pushed out of
the magnetic field. Deprived of magnetic stimulation, it cools down - cooling the water, which is then pumped
around the freezer. While this is happening, the other bed in the magnetic
field is heated. So far, the prototype
Iowa fridge has run for more
than four months without any problem.
Ultimately, like most
refrigerators, it runs on electricity. Power is needed to
move the bed and to keep
the water circulating. But a
commercial version may use
significantly less electricity
than a conventional fridge.
No energy is lost in the
expansion and compression
of the working fluid, and
the magnet that generates
the field is based on a super-conductor and thus consumes negligible quantities
of electricity. The maximum
energy efficiency of a conventional fridge is about
40 per cent. Theoretically,
the new can achieve 60 per
Such a fridge is, however, still a few
years away from being developed for
industrial and domestic applications.
The prototype is expensive. But if it
proves commercially viable, it may be
the coolest fridge around.