Magnetic Cooling Enables Efficient, “Green” Refrigeration 2015-02-06
Magnetic cooling is a promising new
refrigeration technology boasting several advantages, ranging from lower energy
consumption to eliminating the use of hazardous fluids, which combine to make
it a more environmentally friendly option than today’s standard
fluid-compression form of refrigeration.
One novel magnetic cooling approach,
developed by a team of Canadian-Bulgarian researchers, relies on solid magnetic
substances called magnetocaloric materials to act as the refrigerant in
miniaturized magnetic refrigerators. These materials are the key to the
development of a “green” cooling technology whose efficiency is able to scale
directly with the generated magnetocaloric effect.
The magnetocaloric effect is “the thermal
response of a magnetic material to the change of an external magnetic field,
which manifests as a change in its temperature,” said Mohamed Balli, a
researcher in the physics department at the Université de Sherbrooke in Quebec,
Canada.
Ferromagnetic materials, for example, are
known to heat up when magnetized and to cool down when the magnetic field is
removed.
“The presence of a magnetic field makes ferromagnetic materials
become more ordered. This is accompanied by disorder within the atomic lattice,
which causes an increase in the material’s temperature,” Balli said.
“Inversely, the absence of a magnetic field means that the atomic lattice is
more ordered and results in a temperature decrease. Magnetic refrigeration
essentially works by recapturing produced cooling energy via a heat transfer
fluid, such as water.”
The researchers originally set out to
measure the standard magnetocaloric effect in the multiferroic compound
HoMn2O5, because this material possesses an insulating behavior that prevents
energy losses associated with electric currents passing through it when
altering its magnetic field.
But, much to their surprise, they
discovered that a giant magnetocaloric effect can be obtained by simply
rotating a crystal of HoMn2O5 within a constant magnetic field – without
requiring moving it in and out of the magnetic field zone (which is the case
for materials exhibiting standard magnetocaloric effects).
This discovery is an important step toward
the development of magnetic cooling technology, and will likely lead to
efficient, “green” cooling systems for both domestic and industrial
applications. “Using the rotating magnetocaloric effect means that the energy
absorbed by the cooling machine can be largely reduced,” Balli said. “It also
opens the door to building simplified, efficient, and compact magnetic cooling
systems in the future.”
Next, the team plans to explore the
possibility of improving the rotating magnetocaloric effect in HoMn2O5 crystals
and related materials.