07-06-2012, 05:01 PM
Magnetic Refrigeration
magnetic_refrigerator.pdf (Size: 63.74 KB / Downloads: 3)
Magnetic refrigeration is a method of refrigeration based on the magnetocaloric effect.
This effect, discovered in 1881, is defined as the response of a solid to an applied magnetic field
which is apparent as a change in its temperature.1 This effect is obeyed by all transition metals
and lanthanide-series elements. When a magnetic field is applied, these metals, known as
ferromagnets, tend to heat up. As heat is applied, the magnetic moments align. When the field is
removed, the ferromagnet cools down as the magnetic moments become randomly oriented.
Gadolinium, a rare-earth metal, exhibits one of the largest known magnetocaloric effects. It was
used as the refrigerant for many of the early magnetic refrigeration designs. The problem with
using pure gadolinium as the refrigerant material is that it does not exhibit a strong
magnetocaloric effect at room temperature. More recently, however, it has been discovered that
arc-melted alloys of gadolinium, silicon, and germanium are more efficient at room
temperature.
Using the magnetocaloric effect for refrigeration purposes was first investigated in the
mid-1920’s but is just now nearing a point where it could be useful on a commercial scale.1 The
main difference associated with this process is that it is void of a compressor. The compressor is
the most inefficient and expensive part of the conventional gas compression system. In place of
the compressor are small beds containing the magnetocaloric material, a small pump to circulate
the heat transfer fluid, and a drive shaft to move the beds in and out of the magnetic field. The
heat transfer fluid used in this process is water mixed with ethanol instead of the traditional
refrigerants that pose threats to the environment.
A majority of the successful magnetic refrigeration research done to this point was
completed by the Ames Laboratory at the University of Iowa and by the Astronautics
2
Corporation of America in Madison, Wisconsin. Karl Gschneidner and Vitalij Pecharsky of the
Ames Laboratory and Carl Zimm of the Astronautics Corporation have led this research. The
team has developed a working system that uses two beds containing spherical powder of
Gadolinium with water being used as the heat transfer fluid. The magnetic field for this system
is 5 Tesla, providing a temperature span of 38 K. The maximum values obtained from this unit
include a cooling power of 600 Watts, Coefficients of Performance near 15, and efficiency of
approximately 60% of Carnot efficiency.3 Due to the high magnetic field, however, this system
is not applicable for use at home.
The ultimate goal of this technology would be to develop a standard refrigerator for home
use. The use of magnetic refrigeration has the potential to reduce operating cost and
maintenance cost when compared to the conventional method of compressor-based refrigeration.
By eliminating the high capital cost of the compressor and the high cost of electricity to operate
the compressor, magnetic refrigeration can efficiently and economically replace compressorbased
refrigeration. The major advantages to the magnetic refrigeration technology over
compressor-based refrigeration are the design technology, environmental impact, and operating
cost savings.
magnetic_refrigerator.pdf (Size: 63.74 KB / Downloads: 3)
Magnetic refrigeration is a method of refrigeration based on the magnetocaloric effect.
This effect, discovered in 1881, is defined as the response of a solid to an applied magnetic field
which is apparent as a change in its temperature.1 This effect is obeyed by all transition metals
and lanthanide-series elements. When a magnetic field is applied, these metals, known as
ferromagnets, tend to heat up. As heat is applied, the magnetic moments align. When the field is
removed, the ferromagnet cools down as the magnetic moments become randomly oriented.
Gadolinium, a rare-earth metal, exhibits one of the largest known magnetocaloric effects. It was
used as the refrigerant for many of the early magnetic refrigeration designs. The problem with
using pure gadolinium as the refrigerant material is that it does not exhibit a strong
magnetocaloric effect at room temperature. More recently, however, it has been discovered that
arc-melted alloys of gadolinium, silicon, and germanium are more efficient at room
temperature.
Using the magnetocaloric effect for refrigeration purposes was first investigated in the
mid-1920’s but is just now nearing a point where it could be useful on a commercial scale.1 The
main difference associated with this process is that it is void of a compressor. The compressor is
the most inefficient and expensive part of the conventional gas compression system. In place of
the compressor are small beds containing the magnetocaloric material, a small pump to circulate
the heat transfer fluid, and a drive shaft to move the beds in and out of the magnetic field. The
heat transfer fluid used in this process is water mixed with ethanol instead of the traditional
refrigerants that pose threats to the environment.
A majority of the successful magnetic refrigeration research done to this point was
completed by the Ames Laboratory at the University of Iowa and by the Astronautics
2
Corporation of America in Madison, Wisconsin. Karl Gschneidner and Vitalij Pecharsky of the
Ames Laboratory and Carl Zimm of the Astronautics Corporation have led this research. The
team has developed a working system that uses two beds containing spherical powder of
Gadolinium with water being used as the heat transfer fluid. The magnetic field for this system
is 5 Tesla, providing a temperature span of 38 K. The maximum values obtained from this unit
include a cooling power of 600 Watts, Coefficients of Performance near 15, and efficiency of
approximately 60% of Carnot efficiency.3 Due to the high magnetic field, however, this system
is not applicable for use at home.
The ultimate goal of this technology would be to develop a standard refrigerator for home
use. The use of magnetic refrigeration has the potential to reduce operating cost and
maintenance cost when compared to the conventional method of compressor-based refrigeration.
By eliminating the high capital cost of the compressor and the high cost of electricity to operate
the compressor, magnetic refrigeration can efficiently and economically replace compressorbased
refrigeration. The major advantages to the magnetic refrigeration technology over
compressor-based refrigeration are the design technology, environmental impact, and operating
cost savings.
