[attachment=11502]
CHAPTER-1
INTRODUCTION
Magnetic refrigeration is a cooling technology based on the magneto caloric effect. It is an alternate method of producing refrigeration.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. 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.
With rapid phase out of chlorofluorocarbons (CFCs) and hydro chlorofluorocarbons (Huffs), however many researchers and users are looking at an alternative or not in kind technologies for performing heating and cooling duties. The magnetic refrigeration is nothing but the same not in kind technology. The report deals with the construction, working & advantages of the system.
The magnetic refrigeration is based on the magneto-caloric effect i.e. ability of some material to get heated when some magnetic field is applied to them & get cooled when magnetic field is removed.
The currently used refrigeration system i.e. vapor compression refrigeration system is not environmental friendly. Since it is causing depletion of ozone layer & thus promoting Global Warming. Hence alternative system is required.
Compare with the vapor compression refrigeration system, magnetic refrigeration system offers no. of advantages on part of space & efficiency but the main thing is that it is environmental friendly.
This finds great importance now a day because of the world wide ban of environmental damaging substance like chloroflurocarbon, which is used in conventional vapor compression refrigeration. Magnetic refrigeration is based on phenomenon called magneto caloric effect. A quick review of the different stages of development made in magnetic refrigeration is done in this paper.
CHAPTER-2
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).
• 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.
CHAPTER-3
CONSTRUCTION AND WORKING
COMPONENTS REQUIRED
1. Magnets
2. Hot Heat exchanger
3. Cold Heat Exchanger
4. Drive
5. Magneto caloric wheel
1) 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.
2) 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.
3) 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.
4) Drive: - Drive provides the right rotation to the heat to rightly handle it. Due to this heat flows in the right desired direction.
Magneto caloric Wheel: - It forms the structure of the whole device. It joins both the two magnets to work properly.
WORKING PRINCIPLE
When the magnetic material is placed in the magnetic field, the thermometer attached to it shows a high temperature as the temperature of it increases. But on the other side when the magnetic material is removed from the magnetic field, the thermometer shows low temperature as its temperature decreases
• WORKING
The magnetic refrigeration is mainly based on magneto caloric effect according to which some materials change in temperature when they are magnetized and demagnetized. Near the phase transition of the magnetic materials, the adiabatic application of a magnetic field reduces the magnetic entropy by ordering the magnetic moments. This results in a temperature increase of the magnetic material. This phenomenon is practically reversible for some magnetic materials; thus, adiabatic removal of the field revert the magnetic entropy to its original state and cools the material accordingly. This reversibility combined with the ability to create devices with inherent work recovery, makes magnetic refrigeration a potentially more efficient process than gas compression and expansion. The efficiency of magnetic refrigeration can be as much as 50% greater than for conventional refrigerators.
The process is performed as a refrigeration cycle, analogous to the Carnot cycle, and can be described at a starting point whereby the chosen working substance is introduced into a magnetic field (i.e. the magnetic flux density is increased). The working material is the refrigerant, and starts in thermal equilibrium with the refrigerated environment.
Adiabatic magnetization: The substance is placed in an insulated environment. The increasing external magnetic field (+H) causes the magnetic dipoles of the atoms to align, thereby decreasing the material's magnetic entropy and heat capacity. Since overall energy is not lost (yet) and therefore total entropy is not reduced (according to thermodynamic laws), the net result is that the item heats up (T + ΔTad).
Isomagnetic enthalpic transfer: This added heat can then be removed by a fluid like water or helium for example (-Q). 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 (H=0).
Adiabatic demagnetization: The substance is returned to another adiabatic (insulated) 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 (i.e. an adiabatic temperature change).
Isomagnetics 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 (+Q). Once the refrigerant and refrigerated environment is in thermal equilibrium.
CHAPTER-4
COMPONANT OF SYSTEM
• MAGNETIC MATERIALS
Only a limited number of magnetic materials possess a large enough magneto caloric effect to be used in practical refrigeration systems. The search for the "best" materials is focused on rare- earth metals, either in pure form or combined with other metals into alloys and compounds.
The magneto caloric effect is an intrinsic property of a magnetic solid. This thermal response of a solid to the application or removal of magnetic fields is maximized when the solid is near its magnetic ordering temperature.
The magnitudes of the magnetic entropy and the adiabatic temperature changes are strongly dependent upon the magnetic order process: the magnitude is generally small in antiferromagnets, ferrimagnets and spin glass systems.
Currently, alloys of gadolinium producing 3 to 4 K per tesla of change in a magnetic field can be used for magnetic refrigeration or power generation purposes.
Recent research on materials that exhibit a giant entropy change showed that Gd5(SixGe1−x)4, La(FexSi1−x)13Hx and MnFeP1−xAsx alloys, for example, are some of the most promising substitutes for Gadolinium and its alloys (GdDy, GdTy, etc...). These materials are called giant magneto caloric effect materials (GMCE).
Gadolinium and its alloys are the best material available today for magnetic refrigeration near room temperature since they undergo second-order phase transitions which have no magnetic or thermal hysteresis involved.
• REGENERATORS
Magnetic refrigeration requires excellent heat transfer to and from the solid magnetic material. Efficient heat transfer requires the large surface areas offered by porous materials. When these porous solids are used in refrigerators, they are referred to as "regenerators”. Typical regenerator geometries include:

please send me the above mentioned topic

[attachment=11672]
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.
Chapter 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 1 kelvin), as well as the
ranges used in common refrigerators, depending on the design of the system. depending on the design of the system. 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.
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.
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.

PRESENTED BY:
K.Anil Kumar.
L.Subba rao

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[attachment=12447]
ABSTRACT :
The objective of this effort is to determine the feasibility of designing, fabricating and testing a sensor cooler, which uses solid materials as the refrigerant. These materials demonstrate the unique property known as the 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 of temperature applications. The proposed effort includes magneto caloric effect material selection, analyses, design and integration of components into a preliminary design. Benefits of this design are lower cost, longer life, lower weight and higher efficiency because it only requires one moving part - the rotating disk 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 (CFC's/HCFC's). Potential commercial applications include cooling of electronics, super conducting components used in telecommunications equipment (cell phone base stations), home and commercial refrigerators, heat pumps, air conditioning for homes, offices and automobiles, and virtually any place that refrigeration is needed.
INTRODUCTION: Refrigeration:
Definition: Refrigeration is the process of reducing the temperature of any substance below that of the surrounding temperature using some working medium called refrigerants. Initially refrigeration was used in the preservation of foodstuff by preventing bacterial action and this technology was further developed and extended its use in industrial applications. For example cool cutting oil helps in machining operations by lowering the temperature of work piece to prevent overheating, Quenching baths for heat treating operations, pharmaceutical field, etc are some of the industrial applications. Conventional Refrigeration Vs Non-conventional (Magnetic) Refrigeration : In conventional refrigeration system we need a medium for the removal of heat from the refrigerator to the surrounding atmosphere. This medium may be a solid, liquid or a gas. Some of the refrigerants which were used initially are ammonia (NH3), carbon dioxide (CO2), sulphur dioxide (SO2), etc. There are some drawbacks in the use of these refrigerants so refrigerants like F-11, F-12, F-22, F-113, etc are being used which are both economical as well as efficient. Minimum temperature that can be obtained by these refrigerants is 0.71oK by boiling liquid helium under the smallest pressure obtainable. Temperatures below this range can be obtained only by the use of Non-Conventional refrigeration system.
Magnetic refrigeration is the method of refrigeration based on MAGNETOCALORIC EFFECT, which is defined as the response of a solid to an applied magnetic field, which is apparent as a change in its temperature. Instead of ozone-depleting refrigerants and energy-consuming compressors found in conventional vapor-cycle refrigerators, this new style of refrigerator uses iron ammonium alum that heats up when exposed to a magnetic field, then cools down when the magnetic field is removed. NON-CONVENTIONAL REFRIGERATION :
TYPES INCLUDE :
1. Thermo Electric Refrigeration.
2. Acoustic Refrigeration.
3. Magnetic Refrigeration.
MAGNETIC REFRIGERATION:
PRINCIPLE: Magnetic refrigerants heat up when they are subjected to a magnetic field because the second law of thermodynamics states that the entropy - or disorder - of a closed system must increase with time. This is because the electron spins in the atoms of the material are aligned by the magnetic field, which reduces entropy. To compensate for this, the motion of the atoms becomes more random, and the material heats up. In a magnetic refrigerator, this heat would be carried away by water or by air. When the magnetic field is turned off, the electron spins become random again and the temperature of the material falls below that of its surroundings. This allows it to absorb more unwanted heat, and the cycle begins again.
Producing very low temperature through the process of adiabatic demagnetization can do refrigeration. The paramagnetic salt is suspended by a thread in a tube containing a low pressure of gaseous helium to provide thermal communication with the surrounding bath of pumped helium. In operation the liquid helium bath is cooled by pumping to the lowest practical pressure, usually achieving a temperature in the neighborhood of 1oK. The temperature of the paramagnetic salt approaches that of the helium bath by conduction through the exchange gas. Next the magnetic field is turned on, causing heating of the salt and a decrease in entropy of the magnetic ions by virtue of their partial alignment in the direction of the applied field. The heat produced is conducted to the surrounding bath of liquid helium so that the temperature again approaches 1oK. If the magnetic field is increased slowly the heat can flow out, as it is generated-the magnetization being almost isothermal. Next the exchange gas surrounding the sample is removed by pumping, and now, with the salt thermally isolated, the magnetic field is turned off. The temperature of the sample decreases markedly as a consequence of the adiabatic demagnetization, which allows the magnetic ions to regain some of their entropy at the expense of the lattice energy of the salt.
The iron ammonium alum salt, originally in zero field (H=0,S=S1), is magnetized isothermally at the temperature T1, by increasing the magnetic field to H=H1.This magnetization, by orienting the magnetic ions of the salt and thus decreasing their disorder, causes a reduction in entropy from S1 to S2. Now the salt is isothermally isolated from its surroundings and thus when the magnetic field is reduced to zero the process follows the horizontal isentropic line and the temperature falls to 10K.The great decrease in temperature and the close approach zero is a consequence of the peculiar shape of the entropy-temperature relation
WORKING The process flow diagram for the Magnetic Refrigeration system is show in the figure below. The mixture of water and ethanol serves as the heat transfer fluid for the system. The fluid first passes through the hot heat exchanger, which uses air to transfer heat to the atmosphere. The fluid then passes through the copper plates attached to the non-magnetized cooler Magneto caloric beds and loses heat.

[attachment=12496]
ABSTRACT
Ever growing demand of the refrigeration and air conditioning systems in different disciplines expects major modifications in the working mechanisms, which ultimately influences the Environment. The alternate eco-friendly systems are to be designed to overcome the hazards such as ODP, GWP caused by the mechanical refrigeration systems.
This paper discusses about ‘Magnetic Refrigeration’ which is based on the principle of Magnetocaloric Effect. Magnetic refrigeration systems are an environmentally attractive space cooling and refrigeration alternative that do not use a fluorocarbon working fluid.
The newly introduced Adiabatic Demagnetization Refrigerator which uses cyclic cooling promises a clean, pollution free environment with efficient cooling.
KEY WORDS: - ODP, GWP, Magnetocaloric Effect, Adiabatic demagnetization.
1. Introduction
Man has always had a need for preserving food and it has probably been known for a long time that low temperatures allow fresh food to be kept for long periods of time. The first method that was used was to collect and store natural ice during the winter to be used later during the warmer periods of the year. This low temperature preserving is termed as’ Refrigeration’. Now a days, refrigeration applications at the domestic, commercial, industrial level are becoming an integral part. Our changing lifestyle leads to more demand and supply for refrigeration systems. The entire concept of refrigeration is based upon Thermodynamic theory.
1.1 Mechanical Refrigeration system:
A device that transfers heat from a cold body to a warm body, with the aid of an external energy source is called as a Refrigerator. The invention of Joule-Thomson’s cooling effect (i.e. when a fluid is allowed to expand through a nozzle, it gets cooled) and its combination with compression gave rise to the Mechanical/Vapour compression Refrigeration technology.
In such a system, the low temperature (evaporator) reservoir is the cold body and from where the stored substances get cooled and the high temperature reservoir(condenser) is the hot body ,from where the heat is given off to surroundings. The two main types of refrigeration cycles are the refrigerant absorption process and the vapour compressor refrigeration cycle. The compressor cycle absorbs heat in an evaporator when the refrigerant vaporizes. This vapour is then compressed by a compressor and then condensed at the higher pressure in a condenser while emitting heat. The liquefied refrigerant is then returned to the low pressure evaporator via a pressure reducing expansion device. The refrigerant that was initially used was ammonia and this and other refrigerants such as sulphur dioxide, methyl chloride and carbon dioxide were in common use. The introduction of CFC-compounds (halogenated hydrocarbons, Freon©, etc.) refrigerants that were at that time considered to be harmless to humans, environmentally safe and incombustible .CFC-compounds where further developed and rapidly replaced the previously used refrigerants except ammonia.
2. Refrigerants and the Environment
CFC-compounds have a significant destructive effect on the earth's Ozone layer that protects us from the sun's UV-radiation. CFCs are very stable and can disperse high in the stratosphere where they decompose and form free chlorine. The chlorine then acts as a catalyst that reacts with the Ozone.
A replacement has been sought for R11, trichlorofluorinemethane, R12, dichlorofluoromethane and R502 (R115+R22) in refrigeration application. These compounds are considered to be the most damaging to the ozone layer and are also the refrigerants that have the most widespread use. The two main environment concerns are discussed below.
2.1 Ozone Depletion Potential (ODP)
With growing environment hazards, awareness towards a sustainable development is increasing now. One of the serious threats to the environment is the Stratospheric Ozone Layer Depletion. The stratospheric ozone layer plays a beneficial role by absorbing most of the biologically damaging ultraviolet sunlight called UV-B coming towards the earth. Ozone also plays a key role in the temperature regulation of the Earth’s atmosphere. Recent investigations have shown those human made chemicals are responsible for the observed depletion of ozone layer. The Ozone depleting compounds (CFCs and HCFC) contain reactive gaseous atoms of chlorine or bromine. These atoms when leaked from the refrigeration system cause hazard. Although, these molecules are heavier than the molecules of air, the atmospheric air circulation takes these compounds to the stratosphere over a period of time.CFCs are very stable and can disperse high in the stratosphere where they decompose and form free chlorine. The chlorine then acts as a catalyst that reacts with the ozone. Halon (i.e. chlorine and bromine) molecules of CFCs and HCFCs react very rapidly with ozone via their oxide formation and thus decrease in concentration of stratospheric ozone.

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http://en.wikipediawiki/Magnetic_refrigeration
http://chuden.co.jp/english/corporate/pr...107_1.html
http://ashraedoclib/20070727_Emerging.pdf

Magnetic Refrigeration



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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.

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(01-04-2011, 12:53 PM)seminar class Wrote: 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