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Magnetic refrigerator
1. Introduction
Magnetic refrigeration is a cooling technology
based on the magnetocaloric effect.
This technique can be used to attain extremely
low temperatures (well below 1kelvin), as well as
the ranges used in common refrigerators,
depending on the design of the system.
Magnetic refrigeration has been recognized as
being an alternative technology to the
conventional vapor compression technology.
2. History
The effect was discovered in pure iron in 1881 by German
physicist Emil. Warburg.
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.
3. History (contd.)
In 1976, Brown presented first room temperature
refrigerator by applying Magneto Caloric Effect.
After the discovery of the giant magnetocaloric effect
(GMCE) Gd5(Si2Ge2) in 1997 by Gashneidner and
Pecharsky, which increases the MCE, many
researchers concede that it has good future potential.
4. Magneto Caloric Effect
The Magneto caloric effect 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.
In these materials significant change in entropy can
be affected by the application or removal of the
magnetic field.
5. Magnetic Refrigeration Cycle
The steps of a magnetic refrigeration process are
analogous vapour compression refrigeration cycle.
one can see from the figure shown that instead of
compression of a gas, a magnetocaloric material is moved
into a magnetic field and that instead of expansion it is
moved out of the field.
The main difference in both cycles is that the heat
injection and rejection in a gaseous refrigerant is a rather
fast process, because turbulent motion transports heat
very fast. But this is not the case in the solid
magnetocaloric materials.
6.
7. Working of Magnetic Refrigerator
Working Steps
1. Adiabatic magnetization
2. Isomagnetic enthalpic transfer
3. Adiabatic demagnetization
4. Isomagnetic entropic transfer
8. Adiabatic Magnetization
The substance is placed in an insulated
environment. The increasing external magnetic
field causes the magnetic dipoles of the atoms to
align, thereby decreasing the material's magnetic
entropy and heat capacity. Due to this
temperature of magnetocaloric material increases
is increased
9. Isomagnetic Enthalpic Transfer
This added heat can then be removed by a
fluid like water or helium. The magnetic field
is held constant to prevent the dipoles from
reabsorbing the heat. Once sufficiently
cooled, the magnetocaloric material and the
coolant are separated.
10. Adiabatic Demagnetization
The substance is returned to another adiabatic
condition so the total entropy remains constant.
However, this time the magnetic field is decreased,
the thermal energy causes the domains to
overcome the field, and thus the sample cools.
Energy transfers from thermal entropy to magnetic
entropy (disorder of the magnetic dipoles).
11. Isomagnetic Entropic Transfer
The magnetic field is held constant to prevent the
material from heating back up. The material is
placed in thermal contact with the environment
Being refrigerated. Because the working material
is cooler than the refrigerated environment (by
design), heat energy migrates into the working
material.
13. Components of Magnetic Refrigerator
Magnets
Hot Heat exchanger
Cold Heat Exchanger
Drive
Magneto caloric material
14.
15.
16. Magnets
Magnets are the main functioning element
Of the magnetic refrigeration. Magnets
provide the magnetic field to the material so
that they can loose or gain the heat to the
surrounding and from the space to be
cooled respectively.
17. Hot Heat Exchanger
The hot heat exchanger absorbs the heat
from the material used and gives off to the
surrounding. It makes the transfer of heat
much effective.
18. Cold Heat Exchanger
The cold heat exchanger absorbs the heat
from the space to be cooled and gives it to
the magnetic material. It helps to make the
absorption of heat effective.
19. Drive
Drive provides the right motion to the
magnets or magneto caloric material so that
change in magnetic field occurs.
20. Magneto caloric Material
It forms the structure of the whole device.
Its design is made in such a way that
maximum heat transfer occurs.
23. Drawbacks
GMCE materials need to be developed.
Protection of electronic components from magnetic
fields.
Permanent magnets have limited field strength.
Moving machines need high precision.
24. Conclusion
Magnetic refrigeration is undoubtedly a
promising technology that should be
encouraged because of its numerous
advantages, in particular energy saving and
environmental benefits
