01-04-2011, 12:53 PM
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Magnetic Refrigeration
1.0 ABSTRACT
The objective of this effort is to study the Magnetic Refrigeration which uses solid materials as
the refrigerant. These materials demonstrate the unique property known as magneto caloric
effect, which means that they increase and decrease in temperature when
magnetized/demagnetized. This effect has been observed for many years and was used for
cooling near absolute zero. Recently materials are being developed which have sufficient
temperature and entropy change to make them useful for a wide range temperature applications.
Benefits of magnetic refrigeration are lower cost, longer life, lower weight and higher efficiency
because it only requires one moving part-the rotating disc on which the magneto caloric material
is mounted. The unit uses no gas compressor, no pumps, no working fluid, no valves and no
ozone destroying chlorofluorocarbons/hydro chlorofluorocarbons. potential commercial
applications include cooling of electronics, super conducting components used in
telecommunications equipment, home and commercial refrigerator ,heat pumps, air conditioning
for homes, offices and automobiles and virtually any places where refrigeration is needed.
2.0 INTRODUCTION
Magnetic refrigeration is a cooling technology based on the magnetocaloric effect. This
technique can be used to attain extremely low temperatures (well below 1 kelvin), as well as the
ranges used in common refrigerators, depending on the design of the system.
2.1 HISTORY
The effect was discovered in pure iron in 1881 by E. Warburg. Originally, the cooling effect
varied between 0.5 to 2 K/T.
Major advances first appeared in the late 1920s when cooling via adiabatic demagnetization was
independently proposed by two scientists: Debye (1926) and Giauque (1927).
The process was demonstrated a few years later when Giauque and MacDougall in 1933 used it
to reach a temperature of 0.25 K. Between 1933 and 1997, a number of advances in utilization of
the MCE for cooling occurred.
This cooling technology was first demonstrated experimentally by chemist Nobel Laureate
William F. Giauque and his colleague Dr. D.P. MacDougall in 1933 for cryogenic purposes (they
reached 0.25 K)
Between 1933 and 1997, a number of advances occurred which have been described in some
reviews.
In 1997, the first near room temperature proof of concept magnetic refrigerator was
demonstrated by Prof. Karl A. Gschneidner, Jr. by the Iowa State University at Ames
Laboratory. This event attracted interest from scientists and companies worldwide that started
developing new kinds of room temperature materials and magnetic refrigerator designs.
Refrigerators based on the magnetocaloric effect have been demonstrated in laboratories, using
magnetic fields starting at 0.6 T up to 10 teslas. Magnetic fields above 2 T are difficult to
produce with permanent magnets and are produced by a superconducting magnet (1 tesla is about
20,000 times the Earth's magnetic field).
2.2 MAGNETO CALORIC EFFECT
The Magneto caloric effect (MCE, from magnet and calorie) is a magneto-thermodynamic
phenomenon in which a reversible change in temperature of a suitable material is caused by
exposing the material to a changing magnetic field. This is also known as adiabatic
demagnetization by low temperature physicists, due to the application of the process
specifically to affect a temperature drop. In that part of the overall refrigeration process, a
decrease in the strength of an externally applied magnetic field allows the magnetic domains of a
chosen (magnetocaloric) material to become disoriented from the magnetic field by the agitating
action of the thermal energy (phonons) present in the material. If the material is isolated so that
no energy is allowed to (e) migrate into the material during this time (i.e. an adiabatic process),
the temperature drops as the domains absorb the thermal energy to perform their reorientation.
The randomization of the domains occurs in a similar fashion to the randomization at the curie
temperature, except that magnetic dipoles overcome a decreasing external magnetic field while
energy remains constant, instead of magnetic domains being disrupted from internal
ferromagnetism as energy is added.
One of the most notable examples of the magnetocaloric effect is in the chemical element
gadolinium and some of its alloys. Gadolinium's temperature is observed to increase when it
enters certain magnetic fields. When it leaves the magnetic field, the temperature returns to
normal. The effect is considerably stronger for the gadolinium alloy Gd5(Si2Ge2). Praseodymium
alloyed with nickel (Pr
Ni
5) has such a strong magnetocaloric effect that it has allowed scientists
to approach within one thousandth of a degree of absolute zero.
Magnetic Refrigeration is also called as Adiabatic Magnetization.
3.0 CONSTRUCTION AND WORKING
3.1 COMPONENTS REQUIRED
1. Magnets
2. Hot Heat exchanger
3. Cold Heat Exchanger
4. Drive
5. Magneto caloric wheel
Magnetic Refrigeration
1.0 ABSTRACT
The objective of this effort is to study the Magnetic Refrigeration which uses solid materials as
the refrigerant. These materials demonstrate the unique property known as magneto caloric
effect, which means that they increase and decrease in temperature when
magnetized/demagnetized. This effect has been observed for many years and was used for
cooling near absolute zero. Recently materials are being developed which have sufficient
temperature and entropy change to make them useful for a wide range temperature applications.
Benefits of magnetic refrigeration are lower cost, longer life, lower weight and higher efficiency
because it only requires one moving part-the rotating disc on which the magneto caloric material
is mounted. The unit uses no gas compressor, no pumps, no working fluid, no valves and no
ozone destroying chlorofluorocarbons/hydro chlorofluorocarbons. potential commercial
applications include cooling of electronics, super conducting components used in
telecommunications equipment, home and commercial refrigerator ,heat pumps, air conditioning
for homes, offices and automobiles and virtually any places where refrigeration is needed.
2.0 INTRODUCTION
Magnetic refrigeration is a cooling technology based on the magnetocaloric effect. This
technique can be used to attain extremely low temperatures (well below 1 kelvin), as well as the
ranges used in common refrigerators, depending on the design of the system.
2.1 HISTORY
The effect was discovered in pure iron in 1881 by E. Warburg. Originally, the cooling effect
varied between 0.5 to 2 K/T.
Major advances first appeared in the late 1920s when cooling via adiabatic demagnetization was
independently proposed by two scientists: Debye (1926) and Giauque (1927).
The process was demonstrated a few years later when Giauque and MacDougall in 1933 used it
to reach a temperature of 0.25 K. Between 1933 and 1997, a number of advances in utilization of
the MCE for cooling occurred.
This cooling technology was first demonstrated experimentally by chemist Nobel Laureate
William F. Giauque and his colleague Dr. D.P. MacDougall in 1933 for cryogenic purposes (they
reached 0.25 K)
Between 1933 and 1997, a number of advances occurred which have been described in some
reviews.
In 1997, the first near room temperature proof of concept magnetic refrigerator was
demonstrated by Prof. Karl A. Gschneidner, Jr. by the Iowa State University at Ames
Laboratory. This event attracted interest from scientists and companies worldwide that started
developing new kinds of room temperature materials and magnetic refrigerator designs.
Refrigerators based on the magnetocaloric effect have been demonstrated in laboratories, using
magnetic fields starting at 0.6 T up to 10 teslas. Magnetic fields above 2 T are difficult to
produce with permanent magnets and are produced by a superconducting magnet (1 tesla is about
20,000 times the Earth's magnetic field).
2.2 MAGNETO CALORIC EFFECT
The Magneto caloric effect (MCE, from magnet and calorie) is a magneto-thermodynamic
phenomenon in which a reversible change in temperature of a suitable material is caused by
exposing the material to a changing magnetic field. This is also known as adiabatic
demagnetization by low temperature physicists, due to the application of the process
specifically to affect a temperature drop. In that part of the overall refrigeration process, a
decrease in the strength of an externally applied magnetic field allows the magnetic domains of a
chosen (magnetocaloric) material to become disoriented from the magnetic field by the agitating
action of the thermal energy (phonons) present in the material. If the material is isolated so that
no energy is allowed to (e) migrate into the material during this time (i.e. an adiabatic process),
the temperature drops as the domains absorb the thermal energy to perform their reorientation.
The randomization of the domains occurs in a similar fashion to the randomization at the curie
temperature, except that magnetic dipoles overcome a decreasing external magnetic field while
energy remains constant, instead of magnetic domains being disrupted from internal
ferromagnetism as energy is added.
One of the most notable examples of the magnetocaloric effect is in the chemical element
gadolinium and some of its alloys. Gadolinium's temperature is observed to increase when it
enters certain magnetic fields. When it leaves the magnetic field, the temperature returns to
normal. The effect is considerably stronger for the gadolinium alloy Gd5(Si2Ge2). Praseodymium
alloyed with nickel (Pr
Ni
5) has such a strong magnetocaloric effect that it has allowed scientists
to approach within one thousandth of a degree of absolute zero.
Magnetic Refrigeration is also called as Adiabatic Magnetization.
3.0 CONSTRUCTION AND WORKING
3.1 COMPONENTS REQUIRED
1. Magnets
2. Hot Heat exchanger
3. Cold Heat Exchanger
4. Drive
5. Magneto caloric wheel
