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17-02-2010, 03:14 PM
Post: #1
magnetic refrigeration full report

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SYNOPSIS


Magnetic refrigeration is an alternate method of producing refrigeration. 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. And a proto type of magnetic refrigerator that works at room temperature is discussed .the magnetic material is cyclically magnetized and demagnetized by permanent magnets in an adiabatic process. Even water can be used as a heat exchanger and no use harmful gases. The maintenance required for magnetic refrigerator is very small compared to vapor compression refrigeration the different methods of finding magnetocaloriceffect are discussed. Different types of magnetic refrigerants that are commonly used and some of their important features are discussed.
21-02-2010, 05:54 AM
Post: #2
RE: magnetic refrigeration full report
hi there..
can u provide complete details abt this topic for me pls...
24-03-2010, 12:54 PM
Post: #3
RE: magnetic refrigeration full report
Magnetic refrigeration is an alternate method of producing refrigeration. 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. And a proto type of magnetic refrigerator that works at room temperature is discussed .the magnetic material is cyclically magnetized and demagnetized by permanent magnets in an adiabatic process. Even water can be used as a heat exchanger and no use harmful gases. The maintenance required for magnetic refrigerator is very small compared to vapor compression refrigeration the different methods of finding magnetocaloriceffect are discussed. Different types of magnetic refrigerants that are commonly used and some of their important features are discussed.

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01-04-2010, 12:25 PM
Post: #4
RE: magnetic refrigeration full report
Magnetic refrigeration technology could provide a Ëœgreenâ„¢ alternative to traditional energy-guzzling gas-compression fridges and air conditioners.They would require 20-30 percent less energy to run than the best systems currently available, and would not rely on ozone-depleting chemicals or greenhouse gases. magnetic refrigeration system works by applying a magnetic field to a magnetic material - some of the most promising being metallic alloys - causing it to heat up.This excess heat is removed from the system by water, cooling the material back down to its original temperature.When the magnetic field is removed the material cools down even further, The primary reson for magnetic refrigeration is the magnetocaloric effect (MCE), discovered by Warburg in 1881. Specifically, the MCE is "the response of a magnetic solid to a changing magnetic field which is evident as a change in its temperature" (Gschneidner)2. When a magnetic field is applied to a magnetic material, the unpaired spins partially comprising the materialâ„¢s magnetic moment are aligned parallel to the magnetic field. This spin ordering lowers the entropy of the system since disorder has decreased. To compensate for the aligned spins, the atoms of the material begin to vibrate, perhaps in an attempt to randomize the spins and lower the entropy of the system again. In doing so, the temperature of the material increases. Conversely, outside the presence of a file, the spins can return to their more chaotic, higher entropy states, and one then observes a decrease in the materialâ„¢s temperature. The warming and cooling process can be likened to a standard refrigerator which implements compressing and expanding gases for variations in heat exchange and surrounding temperature.


read more
http://ocw.mit.edu/NR/rdonlyres/Material..._paper.pdf
http://ipnpr.jpl.nasa.gov/progress_report/42-78/78D.PDF
http://en.wikipedia.org/wiki/Magnetic_refrigeration
http://www.chuden.co.jp/english/corporat...107_1.html
http://www.ashrae.org/doclib/20070727_Emerging.pdf

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13-07-2010, 10:17 PM
Post: #5
RE: magnetic refrigeration full report
I need full report on magnetic refrigeration
19-07-2010, 06:13 PM
Post: #6
RE: magnetic refrigeration full report
magnetic refrigeration full report
19-07-2010, 07:48 PM
Post: #7
RE: magnetic refrigeration full report
I need magnetic refrigeration full report . Please send it asap.
thanks.....
22-07-2010, 09:20 AM
Post: #8
RE: magnetic refrigeration full report
hey there,
could you plz send me the full details of the project..
22-07-2010, 08:59 PM
Post: #9
RE: magnetic refrigeration full report
can u send me full report
02-08-2010, 12:01 AM
Post: #10
RE: magnetic refrigeration full report

.pdf  Seminar-Report.pdf (Size: 294 KB / Downloads: 833)

Submitted By
Robin Arora Roll No 2103403 Mechanical (4thyr)
Department of Mechanical Engineering Doon Valley Institute Of Engg. & Technology
Karnal - 132001, Haryana (India)
[

MAGNETIC REFRIGERATION
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.

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 who 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 effect 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 (PrNi5) 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.
OBJECTIVES




To develop more efficient and cost effective small scale H2 liquefiers as an alternative to vapor-compression cycles using magnetic refrigeration.


With the help of magnetic refrigeration our objective is to solve the problem of hydrogen storage as it ignites on a very low temperature. Hydrogen Research Institute (HRI) is studying it with the help of magnetic refrigeration. We provide the cooling for the hydrogen storage by liquefying it.


The hydrogen can be liquefied at a low temperature and the low temperature is achieved with the help of magnetic refrigeration.


Thus, the magnetic refrigeration also provides a method to store hydrogen by liquefying it. The term used for such a device is magnetic liquefier.
COMPONENTS

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.
5. Magneto caloric Wheel : - It forms the structure of the whole device. It joins both the two magnets to work properly.
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 reverts 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 + ATad).

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). Energy (and entropy) transfers from thermal entropy to magnetic entropy (disorder of the magnetic dipoles).

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 (+Q).

Once the refrigerant and refrigerated environment are in thermal equilibrium, the cycle begins a new
WORKING PRINCIPLE



As shown in the figure, 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.

PROPER FUNCTIONING


The place we want to cool it, we will apply magnetic field to the material in that place and as its temperature increases, it will absorb heat from that place and by taking the magnetic material outside in the surroundings, we will remove the magnetic material from magnetic field and thus it will loose heat as its temperature decreases and hence the cycle repeats over and again to provide the cooling effect at the desired place.

TECHNICAL


1. HIGH EFFICIENCY : -
As the magneto caloric effect is
highly reversible, the thermo dynamic efficiency of the
magnetic refrigerator is high.
It is some what 50% more than Vapor Compression
cycle.
2. REDUCED COST : -
As it eliminates the most in efficient part of today's refrigerator i.e. comp. The cost reduces as a result.
3. COMPACTNESS : -
It is possible to achieve high energy density compact device. It is due to the reason that in case of magnetic refrigeration the working substance is a social material (say gadolinium) and not a gas as in case of vapor compression cycles.
4. RELIABILITY : - Due to the absence of gas, it reduces concerns related to the emission into the atmosphere and hence is reliable one.
SOCIO-ECONOMIC

1. Competition in global market :-Research in this field will provide the opportunity so that new industries can be set up which may be capable of competing the global or international market.
2. Low capital cost :-The technique will reduce the cost as the most inefficient part comp. is not there and hence the initial low capital cost of the equipment.
3. Key factor to new technologies :-If the
training and hard wares are developed in this field they will be the key factor for new emerging technologies in this world.

Activities
(present and future)


1. Development of optimized magnetic refrigerants
(large magneto caloric effect):-
These days we are trying to
develop the more effective magnetic refrigerators with the help
of some other refrigerants so that large magneto caloric effect
can be produced. This research work is under consideration. We
are trying to find the refrigerant element which can produce the
optimum refrigeration effect.



2. Performance simulations of magnetic refrigerants:-
Under
the research we are studying the performance of various refrigerants and trying to simulate them. This will help us to develop the technology the most and at a faster rate.


3. Design of a magnetic liquefier:-
The storage of hydrogen is
also a big problem. The magnetic liquefier developed so far
solves this problem. The magnetic liquefier is a device based on
magnetic refrigeration which help us to store the hydrogen at a
low temperature and after that it can be used for various
purposes.
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 magnetocaloric 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; it can be substantial for normal ferromagnets which undergo a second order magnetic transition; and it is generally the largest for a ferromagnet which undergoes a first order magnetic transition.

Also, crystalline electric fields and pressure can have a substantial influence on magnetic entropy and adiabatic temperature changes.
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)DH 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 magnetocaloric 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:
(a) Tubes
(b) Perforated plates
© Wire screens
(d) Particle beds

Super Conducting Magnets


Most practical magnetic refrigerators are based on superconducting magnets operating at cryogenic temperatures (i.e., at -269 C or 4 K).These devices are electromagnets that conduct electricity with essentially no resistive losses. The superconducting wire most commonly used is made of a Niobium-Titanium alloy.
Only superconducting magnets can provide
sufficiently strong magnetic fields for most refrigeration applications.
A typical field strength is 8 Tesla (approximately 150,000 times the Earth's magnetic field).An 8 Tesla field can produce a magneto caloric temperature change of up to 15 C in some rare-earth materials.

Active Magnetic Regenerators (AMR's)


A regenerator that undergoes cyclic heat transfer operations and the magneto caloric effect is called an Active Magnetic Regenerator (AMR).An AMR should be designed to possess the following attributes:
These requirements are often contradictory, making AMR's difficult to design and fabricate.
1. High heat transfer rate
2. Low pressure drop of the heat transfer fluid
3. High magneto caloric effect
4. Sufficient structural integrity
5. Low thermal conduction in the direction of fluid flow
6. Low porosity
7. Affordable materials
8. Ease of manufacture
A Rotary AMR Liquefier



The Cryofuel Systems Group at UVic is developing an AMR refrigerator for the purpose of liquefying natural gas. A rotary configuration is used to move magnetic material into and out of a superconducting magnet.
This technology can also be extended to the liquefaction of hydrogen.

COMPARISON


The magneto caloric effect can be utilized in a thermodynamic cycle to produce refrigeration. Such a cycle is analogous to conventional gas-compression refrigeration:

The added advantages of MR over Gas Compression Refrigerator are compactness, and higher reliability due to Solid working materials instead of a gas, and fewer and much slower moving parts our work in this field is geared toward the development of magnetic alloys with MCEs, and phase transitions temperatures suitable for hydrogen liquefaction from Room temperature down to 20 K.
We are also collaborating with The University of Victoria (British Columbia, Canada), on the development of an experimental system to prove the technology.

ADVANTAGES OVER VAPOUR COMPRESSION

CYCLES:-


Magnetic refrigeration performs essentially the same task as traditional compression-cycle gas refrigeration technology. Heat and cold are not different qualities; cold is merely the relative absence of heat. In both technologies, cooling is the subtraction of heat from one place (the interior of a home refrigerator is one commonplace example) and the dumping of that heat another place (a home refrigerator releases its heat into the surrounding air). As more and more heat is subtracted from this target, cooling occurs. Traditional refrigeration systems - whether air-conditioning, freezers or other forms - use gases that are alternately expanded and compressed to perform the transfer of heat. Magnetic refrigeration systems do the same job, but with metallic compounds, not gases. Compounds of the element gadolinium are most commonly used in magnetic refrigeration, although other compounds can also be used


Magnetic refrigeration is seen as an environmentally friendly alternative to conventional vapor-cycle refrigeration. And as it eliminates the need for the most inefficient part of today's

refrigerators, the compressor, it should save costs. New materials described in this issue may bring practical magneto caloric cooling a step closer. A large magnetic entropy change has been found to occur in MnFeP0.45As0.55 at room temperature, making it an attractive candidate for commercial applications in magnetic refrigeration.

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09-08-2010, 10:49 PM
Post: #11
RE: magnetic refrigeration full report
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12-08-2010, 01:35 PM
Post: #12
RE: magnetic refrigeration full report
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23-08-2010, 09:41 PM
Post: #13
RE: magnetic refrigeration full report
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02-09-2010, 11:34 AM
Post: #14
RE: magnetic refrigeration full report
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28-09-2010, 10:32 AM
Post: #15
RE: magnetic refrigeration full report

.doc  28374599-Seminar-Report.doc (Size: 301 KB / Downloads: 311)
.pptx  MAGNETIC REFRIGERATION.pptx (Size: 361.77 KB / Downloads: 326)
This article is presented by:
NUSRATH AHAMED.
3VC06ME025
Dept of Mechanical Engg
R.Y.M.E.C
BELLARI

MAGNETIC REFRIGERATION


OBJECTIVE

To develop more efficient and cost-effective small-scale H2 liquefiers as an alternative to vapour-compression cycles using magnetic refrigeration (adiabatic magnetization).
INTRODUCTION

Magnetic refrigeration is a physical process that exploits the magnetic properties of certain solid materials to produce refrigeration.

Magnetic refrigeration is a cooling technology based on the magneto caloric 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.

HISTORY

Magneto caloric effect was discovered in pure iron in 1881 by
E. Warburg.
Debye (1926) & Giauque (1927) proposed a improved technique of cooling via adiabatic demagnetization independently.
The cooling technology was first demonstrated experimentally in 1933 by chemist Nobel Laureate William F. Giauque & his colleague Dr. D. P. MacDougall for cryogenic purposes.
In 1997, Prof. Karl A. Gschneidner, Jr. by the Iowa State University at Ames Laboratory, demonstrated the first near room temperature proof of concept magnetic refrigerator.


29-10-2010, 12:25 AM
Post: #16
RE: magnetic refrigeration full report
MAGNETIC REFRIGERATION
REPORT OF THE SEMINAR
Submitted by
HARI KRISHNAN.K.S
DEPARTMENT OF MECHANICAL ENGINEERING
P. A. AZIZ COLLEGE OF ENGINEERING & TECHNOLOGY



1. INTRODUCTION
Magnetic refrigeration is a cooling technology based on the magneto caloric 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. 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.



.docx  MAGNETIC REFRIGERATION.docx (Size: 191.33 KB / Downloads: 500)




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).






2.1 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 (PrNi5) 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. CONSTRUCTION AND WORKING

3.1 COMPONENTS REQUIRED
1. Magnets
2. Hot Heat exchanger
3. Cold Heat Exchanger
4. Drive
5. Magneto caloric wheel

Fig3.1.1rotary-magnetic-refrigeration

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.
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.
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.
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.

3.2 WORKING PRINCIPLE

As shown in the figure 3.2.1, 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
Fig 3.2.1 Principle
3.3 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.
Fig 3.3.1. Working
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). Energy (and entropy) transfers from thermal entropy to magnetic entropy (disorder of the magnetic dipoles).
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 (+Q). Once the refrigerant and refrigerated environment is in thermal equilibrium, the cycle begins a new one.



3.4 PROPER FUNCTIONING

The place we want to cool it, we will apply magnetic field to the material in that place and as its temperature increases, it will absorb heat from that place and by taking the magnetic material outside in the surroundings, we will remove the magnetic material from magnetic field and thus it will loose heat as its temperature decreases and hence the cycle repeats over and again to provide the cooling effect at the desired place.
3.4.1. WORKING MATERIALS
The magnetocaloric 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; it can be substantial for normal ferromagnets which undergo a second order magnetic transition; and it is generally the largest for a ferromagnet which undergoes a first order magnetic transition.
Also, crystalline electric fields and pressure can have a substantial influence on magnetic entropy and adiabatic temperature changes.
Currently, alloys of gadolinium producing 3 to 4 K per tesla (K/T) 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 magnetocaloric 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.



4.0 REQUIREMENTS FOR PRATICAL APPLICATIONS

4.1 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.


4.2 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:
(a) Tubes
(b) Perforated plates
© Wire screens
(d) Particle beds



Fig 4.2.1. Regenerators

4.3 SUPER CONDUCTING MAGNETS
Most practical magnetic refrigerators are based on superconducting magnets operating at cryogenic temperatures (i.e., at -269 C or 4 K).These devices are electromagnets that conduct electricity with essentially no resistive losses. The superconducting wire most commonly used is made of a Niobium-Titanium alloy.
Only superconducting magnets can provide sufficiently strong magnetic fields for most refrigeration applications. A typical field strength is 8 Tesla (approximately 150,000 times the Earth's magnetic field).An 8 Tesla field can produce a magneto caloric temperature change of up to 15 C in some rare-earth materials.

Fig 4.3.1 superconducting magnets
4.4Active Magnetic Regenerators (AMR's)
A regenerator that undergoes cyclic heat transfer operations and the magneto caloric effect is called an Active Magnetic Regenerator (AMR).An AMR should be designed to possess the following attributes:
These requirements are often contradictory, making AMR's difficult to design and fabricate.
1. High heat transfer rate
2. Low pressure drop of the heat transfer fluid
3. High magneto caloric effect
4. Sufficient structural integrity
5. Low thermal conduction in the direction of fluid flow
6. Low porosity
7. Affordable materials
8. Ease of manufacture

5. APPLICATIONS

5.1 A rotary AMR liquefier
The Cryofuel Systems Group is developing an AMR refrigerator for the purpose of liquefying natural gas. A rotary configuration is used to move magnetic material into and out of a superconducting magnet. This technology can also be extended to the liquefaction of hydrogen.

5.2 Future Applications

In general, at the present stage of the development of magnetic refrigerators with permanent magnets, hardly any freezing applications are feasible. These results, because large temperature spans occur between the heat source and the heat sink.
An option to realize magnetic freezing applications could be the use of superconducting magnets.However, this may only be economic in the case of rather large refrigeration units. Such are usedfor freezing, e.g. in cooling plants in the food industry or in large marine freezing applications
Some of the future applications are
1. Magnetic household refrigeration appliances
2. Magnetic cooling and air conditioning in buildings and houses
3. Central cooling system
4. Refrigeration in medicine
5. Cooling in food industry and storage
6. Cooling in transportation
7. Cooling of electronics



6.0 COMPARISON

6.1 Comparison between magnetic refrigeration and conventional refrigeration

The magneto caloric effect can be utilized in a thermodynamic cycle to produce refrigeration. Such a cycle is analogous to conventional gas-compression refrigeration .



Fig 6.1.1 Comparison between magnetic refrigeration and conventional refrigeration

Co-efficient of Performance of magnetic refrigeration is given by the equation
COP= Qc/Win
Qc is the cooling power i.e. the heat absorbed from the cold end.
Win is the work input into magnetic refrigerator.

7. BENEFITS

7.1 TECHNICAL

High efficiency: - As the magneto caloric effect is highly reversible, the thermo dynamic efficiency of the magnetic refrigerator is high. It is somewhat 50% more than Vapor Compression cycle.
Reduced operating cost: - As it eliminates the most inefficient part of today’s refrigerator i.e. comp. The cost reduces as a result.
Compactness: - It is possible to achieve high energy density compact device. It is due to the reason that in case of magnetic refrigeration the working substance is a solid material (say gadolinium) and not a gas as in case of vapor compression cycles.
Reliability: - Due to the absence of gas, it reduces concerns related to the emission into the atmosphere and hence is reliable one.
7.2 SOCIO-ECONOMIC
Competition in global market:-Research in this field will provide the opportunity so that new industries can be set up which may be capable of competing the global or international market.
Low capital cost:-The technique will reduce the cost as the most inefficient part comp. is not there and hence the initial low capital cost of the equipment.
Key factor to new technologies:-If the training and hard wares are developed in this field they will be the key factor for new emerging technologies in this world




7.3 ADVANTAGES OVER VAPOUR COMPRESSION AND VAPOR ABSORPTION CYCLE CYCLES

Magnetic refrigeration performs essentially the same task as traditional compression-cycle gas refrigeration technology. Heat and cold are not different qualities; cold is merely the relative absence of heat. In both technologies, cooling is the subtraction of heat from one place (the interior of a home refrigerator is one commonplace example) and the dumping of that heat another place (a home refrigerator releases its heat into the surrounding air). As more and more heat is subtracted from this target, cooling occurs. Traditional refrigeration systems - whether air-conditioning, freezers or other forms - use gases that are alternately expanded and compressed to perform the transfer of heat. Magnetic refrigeration systems do the same job, but with metallic compounds, not gases. Compounds of the element gadolinium are most commonly used in magnetic refrigeration, although other compounds can also be used.
Magnetic refrigeration is seen as an environmentally friendly alternative to conventional vapor- cycle refrigeration. And as it eliminates the need for the most inefficient part of today's refrigerators, the compressor, it should save costs. New materials described in this issue may bring practical magneto caloric cooling a step closer. A large magnetic entropy change has been found to occur in MnFeP0.45As0.55 at room temperature, making it an attractive candidate for commercial applications in magnetic refrigeration.
The added advantages of MR over Gas Compression Refrigerator are compactness, and higher reliability due to Solid working materials instead of a gas, and fewer and much slower moving parts our work in this field is geared toward the development of magnetic alloys with MCEs, and phase transitions temperatures suitable for hydrogen liquefaction from Room temperature down to 20 K.




7.4 Disadvantages of vapor compression and vapor absorption refrigeration

1. Produces toxic gases and chloro-fluoro carbon, thus reducing ozone layer
depletion.
2. Very low temperature of order 001K cannot be achieved.
3. The unit produces noise and vibration compared to magnetic refrigerators.
4. Compressor is needed to produce required pressure.
5. An unnecessarily large motor is required to overcome the inertia of the stationary
compressor in case of heavy load applications
6. Large torque loads are placed on the motor, compressor mounts, bearings and belts at start up.
7. In the lithium bromide absorption refrigeration system, lithium bromide is corrosive in nature and in case of the ammonia system, ammonia is toxic, flammable.
















8. CURRENT AND FUTURE USES
There are still some thermal and magnetic hysteresis problems to be solved for these first-order phase transition materials that exhibit the GMCE to become really useful; this is a subject of current research. A useful review on magneto caloric materials published in 2005 is entitled "Recent developments in magneto caloric materials" by Dr. Karl A. Gschneidner, .This effect is currently being explored to produce better refrigeration techniques, especially for use in spacecraft. This technique is already used to achieve cryogenic temperatures in the laboratory setting (below 10K). As an object displaying MCE is moved into a magnetic field, the magnetic spins align, lowering the entropy. Moving that object out of the field allows the object to increase its entropy by absorbing heat from the environment and disordering the spins. In this way, heat can be taken from one area to another. Should materials be found to display this effect near room temperature, refrigeration without the need for compression may be possible, increasing energy efficiency.
In addition, magnetic refrigeration could also be used in domestic refrigerators. In 2006, a research group led by Karl Sandeman at the University of Cambridge made a new alloy, composed of cobalt, manganese, silicon and germanium that can be used for magnetic refrigeration. This has made the use of the expensive material gadolinium redundant, and made the creation of domestic magnetic refrigerators possible. The use of this technology for domestic refrigerators though is very remote due to the high efficiency of current Vapor-compression refrigeration in the range of 60% of Carnots efficiency. Gas molecules are responsible for heat transfer, they absorb heat in the inner side of the refrigerator by expanding and release this heat in the outside by condensing. The work provided to do this work is a cheap and highly efficient compressor, driven by an electric motor that is more than 80% efficient. This technology could eventually compete with other cryogenic heat pumps for gas liquefaction purposes.








9. CASE STUDY
T. Utaki, T. Nakagawa T. A. Yamamoto and T. Numazawa from Graduate school of Engineering, Osaka University Osaka, 565-0871, Japan and K. Kamiya from National Institute for Materials Science, Tsukuba Magnet Laboratory ,Tsukuba, Ibaraki, 305-0003, Japan have constructed a Active Magnetic Regenerative(AMR) cycle for liquefaction of hydrogen.
The magnetic refrigerator model they have constructed is based on a multistage active magnetic regenerative (AMR) cycle. In their model, an ideal magnetic material with constant magneto caloric effect is employed as the magnetic working substance. The maximum applied magnetic field is 5T, and the liquid hydrogen production rate is 0.01t/day. Starting from liquid nitrogen temperature (77K), it is assumed that four separate four stages of refrigeration are needed to cool the hydrogen. The results of the simulation show that the use of a magnetic refrigerator for hydrogen liquefaction is possibly more than the use of conventional liquefaction methods.
In general, they have found that, it is helpful to pre cool hydrogen prior to liquefaction using a cryogenic liquid such as Liquid nitrogen (LN) or liquid natural gas (LNG).Therefore, we chose three system configurations to analyze with our numerical simulation. In the first case, the supplied hydrogen is precooled by the AMRR only. In this case it is assumed that the magnetic refrigeration system precools the hydrogen from 300 K to 22 K using approximately 7-9 stages of AMRR. In the second case, the supplied hydrogen is precooled from 300 K to 77 K by LN and from 77 K to 22 K by 3 stages of AMRR. In the third case, the supplied hydrogen is precooled from 300 K to120 K by LNG and from 120 K to 22 K by 5 stages of AMRR. The best performance was achieved by a combined CMR plus a 3-stage AMRR with LN precooling. It had a total work input of 3.52 kW and had a liquefaction efficiency of 46.9 %. This provides promise that magnetic refrigeration systems may be able to achieve higher efficiency than conventional liquefaction methods

10. CONCLUSION
Magnetic refrigeration is a technology that has proven to be environmentally safe. models have shown 25% efficiency improvement over vapor compression systems. In order to make the Magnetic Refrigerator commercially viable, scientists need to know how to achieve larger temperature swings. Two advantages to using Magnetic Refrigeration over vapor compressed systems are no hazardous chemicals used and they can be up to 60% efficient.
There are still some thermal and magnetic hysteresis problems to be solved for these first-order phase transition materials that exhibit the GMCE to become really useful; this is a subject of current research. This effect is currently being explored to produce better refrigeration techniques, especially for use in spacecraft. This technique is already used to achieve cryogenic temperatures in the laboratory setting (below 10K).















11. REFERENCES

1. http://en.wikipedia.org/wiki/Magnetic_refrigeration
2. http://www.scribd.com/doc/19537314/Magne...rigeration
3. Lounasmaa, experimental principles and methods, academic press
4. Richardson and Smith, experimental techniques in condensed matter physics at low temperature, Addison Wesley (2003)
5. A text book on cryogenic engineering by V.J.Johnson
6. “Refrigeration and Air conditioning” by Arora and Domkundwar
7. Magnetic Refrigeration, ASHRAE Journal (2007), by John Dieckmann, Kurt Roth and James Brodrick


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23-12-2010, 12:18 PM
Post: #17
RE: magnetic refrigeration full report
Prepared by::ELDHOSE KURIAN


INTRODUCTION
Magnetic refrigeration is a cooling technology based on the magneto caloric effect.
Invented by Emil Warburg in 1880
Used to attain cryogenic temperatures well below 1o K with the help of magnetic fields
PRINCIPLE OF MAGNETIC REFRIGERATION
Magneto caloric effect is the basic principle on which the cooling is achieved.
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.
This is called adiabatic demagnetisation .
THERMODYNAMIC CYCLE
STEPS OF THERMODYNAMIC CYCLE
Adiabatic magnetisation
Isomagnetic enthalpic transfer
Adiabatic demagnetization
Isomagnetic entropic transfer

REQUIREMENTS FOR PRACTICAL APPLICATIONS
Magnetic Materials
Regenerators
Super Conducting Magnets
Active Magnetic Regenerators(AMR’s)
MAGNETIC MATERIALS
Magnetocaloric effect is an intrinsic property of a substance
Gadolinium and its alloys are the best materials available for magnetic refrigeration
They can reach ultra low temperatures
REGENERATORS
Efficient heat transfer requires large surface areas offered by porous materials
When these porous materials are used in refrigerators they are referred to as regenerators


SUPER CONDUCTING MAGNETS
The magnetic field is created by superconducting magnets
Most practical magnetic refrigerators are based on super conducting magnets operating at cryogenic temperatures
Commonly used is made of a Niobium-Titanium alloy
ACTIVE MAGNETIC REGENERATORS
A regenerator that undergoes cyclic heat transfer operations and magneto caloric effect is called Active Magnetic Regenerator
It should be designed to possess:
high heat transfer rate
high magneto calorific effect
affordable materials
ease of manufacture

APPLICATIONS


Liquefaction purposes in the case of hydrogen,nitrogen and helium
Also focuses on many future applications like magnetic household refrigeration,cooling in transportation,cooling electronic circuits etc.


MERITS
High efficiency
Reduced operating cost
Reliability
CONCLUSIONS


Magnetic refrigeration is a technology that has proven to be environmentally safe
In order to make the Magnetic Refrigerator commercially viable, scientists need to know how to achieve larger temperature swings and also permanent magnets which can produce strong magnetic fields of order 10 tesla
There are still some thermal and magnetic hysteresis problems to be solved for the materials that exhibit the MCE to become really useful


REFERENCES
http://en.wikipedia.org/wiki/Magnetic refrigeration
A text book on Refrigeration and Air conditioning by C P Arora and Domkundwar
A text book on Cryogenic Engineering by Thomas M. Flynn


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20-01-2011, 12:29 PM
Post: #18
RE: magnetic refrigeration full report



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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.
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 who 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 CAROIC 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 effect 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 (PrNi5) 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.


OBJECTIVES

To develop more efficient and cost effective small scale H2 liquefiers as an alternative to vapor-compression cycles using magnetic refrigeration.

With the help of magnetic refrigeration our objective is to solve the problem of hydrogen storage as it ignites on a very low temperature. Hydrogen Research Institute (HRI) is studying it with the help of magnetic refrigeration. We provide the cooling for the hydrogen storage by liquefying it.

The hydrogen can be liquefied at a low temperature and the low temperature is achieved with the help of magnetic refrigeration.

Thus, the magnetic refrigeration also provides a method to store hydrogen by liquefying it. The term used for such a device is magnetic liquefier.



COMPONENTS

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.

5. Magneto caloric Wheel : - It forms the structure of the whole device. It joins both the two magnets to work properly.


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 reverts 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). Energy (and entropy) transfers from thermal entropy to magnetic entropy (disorder of the magnetic dipoles).
• 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 (+Q).
Once the refrigerant and refrigerated environment are in thermal equilibrium, the cycle begins a new

WORKING PRINCIPLE

As shown in the figure, 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.

PROPER FUNCTIONING

The place we want to cool it, we will apply magnetic field to the material in that place and as its temperature increases, it will absorb heat from that place and by taking the magnetic material outside in the surroundings, we will remove the magnetic material from magnetic field and thus it will loose heat as its temperature decreases and hence the cycle repeats over and again to provide the cooling effect at the desired place.

BENEFITS
TECHNICAL


1. HIGH EFFICIENCY : - As the magneto caloric effect is highly reversible, the thermo dynamic efficiency of the magnetic refrigerator is high.
It is some what 50% more than Vapor Compression cycle.

2. REDUCED COST : - As it eliminates the most in efficient part of today’s refrigerator i.e. comp. The cost reduces as a result.

3. COMPACTNESS : - It is possible to achieve high energy density compact device. It is due to the reason that in case of magnetic refrigeration the working substance is a social material (say gadolinium) and not a gas as in case of vapor compression cycles.

4. RELIABILITY : - Due to the absence of gas, it reduces concerns related to the emission into the atmosphere and hence is reliable one.

BENEFITS
SOCIO-ECONOMIC


1. Competition in global market :-Research in this field will provide the opportunity so that new industries can be set up which may be capable of competing the global or international market.

2. Low capital cost :-The technique will reduce the cost as the most inefficient part comp. is not there and hence the initial low capital cost of the equipment.

3. Key factor to new technologies :-If the training and hard wares are developed in this field they will be the key factor for new emerging technologies in this world.

Activities
(present and future)


1. Development of optimized magnetic refrigerants (large magneto caloric effect):- These days we are trying to develop the more effective magnetic refrigerators with the help of some other refrigerants so that large magneto caloric effect can be produced. This research work is under consideration. We are trying to find the refrigerant element which can produce the optimum refrigeration effect.

2. Performance simulations of magnetic refrigerants:-Under the research we are studying the performance of various refrigerants and trying to simulate them. This will help us to develop the technology the most and at a faster rate.

3. Design of a magnetic liquefier:- The storage of hydrogen is also a big problem. The magnetic liquefier developed so far solves this problem. The magnetic liquefier is a device based on magnetic refrigeration which help us to store the hydrogen at a low temperature and after that it can be used for various purposes.

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 magnetocaloric 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; it can be substantial for normal ferromagnets which undergo a second order magnetic transition; and it is generally the largest for a ferromagnet which undergoes a first order magnetic transition.
Also, crystalline electric fields and pressure can have a substantial influence on magnetic entropy and adiabatic temperature changes.
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 magnetocaloric 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:

(a) Tubes
(b) Perforated plates
© Wire screens
(d) Particle beds

Super Conducting Magnets

Most practical magnetic refrigerators are based on superconducting magnets operating at cryogenic temperatures (i.e., at -269 C or 4 K).These devices are electromagnets that conduct electricity with essentially no resistive losses. The superconducting wire most commonly used is made of a Niobium-Titanium alloy.
Only superconducting magnets can provide sufficiently strong magnetic fields for most refrigeration applications.
A typical field strength is 8 Tesla (approximately 150,000 times the Earth's magnetic field).An 8 Tesla field can produce a magneto caloric temperature change of up to 15 C in some rare-earth materials.

Active Magnetic Regenerators (AMR's)

A regenerator that undergoes cyclic heat transfer operations and the magneto caloric effect is called an Active Magnetic Regenerator (AMR).An AMR should be designed to possess the following attributes:
These requirements are often contradictory, making AMR's difficult to design and fabricate.
1. High heat transfer rate

2. Low pressure drop of the heat transfer fluid

3. High magneto caloric effect

4. Sufficient structural integrity

5. Low thermal conduction in the direction of fluid flow

6. Low porosity

7. Affordable materials

8. Ease of manufacture
A Rotary AMR Liquefier

The Cryofuel Systems Group at UVic is developing an AMR refrigerator for the purpose of liquefying natural gas. A rotary configuration is used to move magnetic material into and out of a superconducting magnet.
This technology can also be extended to the liquefaction of hydrogen.

COMPARISON

The magneto caloric effect can be utilized in a thermodynamic cycle to produce refrigeration. Such a cycle is analogous to conventional gas-compression refrigeration:


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The added advantages of MR over Gas Compression Refrigerator are compactness, and higher reliability due to Solid working materials instead of a gas, and fewer and much slower moving parts our work in this field is geared toward the development of magnetic alloys with MCEs, and phase transitions temperatures suitable for hydrogen liquefaction from Room temperature down to 20 K.
We are also collaborating with The University of Victoria (British Columbia, Canada), on the development of an experimental system to prove the technology.

ADVANTAGES OVER VAPOUR COMPRESSION CYCLES:-

Magnetic refrigeration performs essentially the same task as traditional compression-cycle gas refrigeration technology. Heat and cold are not different qualities; cold is merely the relative absence of heat. In both technologies, cooling is the subtraction of heat from one place (the interior of a home refrigerator is one commonplace example) and the dumping of that heat another place (a home refrigerator releases its heat into the surrounding air). As more and more heat is subtracted from this target, cooling occurs. Traditional refrigeration systems - whether air-conditioning, freezers or other forms - use gases that are alternately expanded and compressed to perform the transfer of heat. Magnetic refrigeration systems do the same job, but with metallic compounds, not gases. Compounds of the element gadolinium are most commonly used in magnetic refrigeration, although other compounds can also be used

Magnetic refrigeration is seen as an environmentally friendly alternative to conventional vapor-cycle refrigeration. And as it eliminates the need for the most inefficient part of today's refrigerators, the compressor, it should save costs. New materials described in this issue may bring practical magneto caloric cooling a step closer. A large magnetic entropy change has been found to occur in MnFeP0.45As0.55 at room temperature, making it an attractive candidate for commercial applications in magnetic refrigeration.



19-02-2011, 11:09 PM
Post: #19
RE: magnetic refrigeration full report
:-/:huh:thank you
pleas i need help withMagnetic Refrigeration
28-02-2011, 10:53 AM
Post: #20
RE: magnetic refrigeration full report
plz send me magnetic refrigeration ppt urgent
28-02-2011, 11:54 PM
Post: #21
RE: magnetic refrigeration full report
hi vicky97854,

this page itself contains a ppt on this topic. please follow the link:
http://www.seminarprojects.com/Thread-ma...1#pid31781
01-03-2011, 08:01 PM
Post: #22
RE: magnetic refrigeration full report
pls send me full report for the above topic
15-03-2011, 08:49 PM
Post: #23
RE: magnetic refrigeration full report
Magnetic Refrigeration
Feby Philip Abraham , Ananthu Sivan
S4 Departement of Mechanical Engineering
Mohandas College Of Engineering and Technology


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Abstract
A cooling system consists of a device or devices used to lower the temperature of a defined region in space through
some cooling process. Currently, the most popular commercial cooling agent is the refrigerant. A refrigerant in its
general sense is what makes refrigerator cool foods, and it also makes air conditioners and other appliances
perform their respective duties. A typical consumer based refrigerator lowers temperatures by modulating a gas
compression-expansion cycle, to cool a refrigerant fluid which has been warmed by the contents of the refrigerator
(i.e. the food inside). Typical refrigerants used in refrigerators include ammonia, methyl chloride, and sulfur
dioxide, all of which are toxic. To mitigate the risks associated with toxic refrigerants, a collaboration by
Frigidaire, General Motors, and DuPont netted the development of Freon (or R12), a chlorofluorocarbon. Freon is
a non-flammable and non-toxic, but ozone- depleting gas. Because of the damaging effects of Freon to the ozone
layer, there has been much interest in targeting other refrigerants. The popular refrigerant R134a (called Suva by
DuPont) is currently used in most refrigerators, but American and international laws are beginning to phase out
this refrigerant as well. The future seems ripe for new refrigeration technology. This has led the world to look for a
better source of refrigeration, and magnetic refrigeration is certainly one of the best options if we consider the
environmental aspects. There are two attractive reasons why magnetic refrigeration research continues. While a
magnetic refrigerator would cost more than today's refrigerator at purchase, it could conserve over and above 20%
more energy than current expansion-compression refrigerators, drastically reducing operating costs. The other
attraction to magnetic refrigeration is the ecological impact a magnetic refrigerator would bring should it supplant
current technologies. Not only would ozone-depleting refrigerant concerns be calmed, but the energy savings itself
would lessen the strain our household appliances put on our environment.

Introduction
Magnetic refrigeration is a cooling technology based
on the magneto caloric 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. The fundamental principle was suggested by
Debye (1926) and Giauque (1927) and the first
working magnetic refrigerators were constructed by
several groups beginning in 1933. Magnetic
refrigeration was the first method developed for
cooling below about 0.3 Kelvin (a temperature
attainable by3He/4He dilution refrigeration).
The Magnetocaloric Effect
The Magnetocaloric 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 effect 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 (PrNi5) has such a strong
magnetocaloric effect that it has allowed scientists to
approach within one thousandth of a degree of
Components required for construction

Magnets: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
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
Cold Heat Exchanger:The cold heat exchanger
absorbs the heat from the space to be cooled and


Magnetic Refrigeration Cycle
The cycle 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'smagneticentrop y 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). Energy (and entropy) transfers from thermal
entropy to magnetic entropy (disorder of the
magnetic dipoles).
•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 (+Q).
Once the refrigerant and refrigerated environment is
in thermal equilibrium, the cycle begins anew

Applied Technique
The basic operating principle of an ADR is the use of
a strong magnetic field to control the entropy of a
sample of material, often called the "refrigerant".
Magnetic field constrains the orientation of magnetic
dipoles in the refrigerant. The stronger the magnetic
field, the more aligned the dipoles are, and this
corresponds to lower entropy and heat capacity
because the material has (effectively) lost some of its
internal degrees of freedom. If the refrigerant is kept
at a constant temperature through thermal contact
with a heat sink (usually liquid helium) while the
magnetic field is switched on, the refrigerant must
lose some energy because it is equilibrated with the
heat sink. When the magnetic field is subsequently
switched off, the heat capacity of the refrigerant rises
again because the degrees of freedom associated with
orientation of the dipoles are once again liberated,
pulling their share of equipartitioned energy from the
motion of the molecules, thereby lowering the overall
temperature of a system with decreased energy. Since
the system is now insulated when the magnetic field
is switched off, the process is adiabatic, i.e. the
system can no longer exchange energy with its
surroundings (the heat sink), and its temperature
decreases below its initial value, that of the heat sink.
The operation of a standard ADR proceeds roughly
as follows. First, a strong magnetic field is applied to
the refrigerant, forcing its various magnetic dipoles to
align and putting these degrees of freedom of the
refrigerant into a state of lowered entropy. The heat
sink then absorbs the heat released by the refrigerant
due to its loss of entropy. Thermal contact with the
heat sink is then broken so that the system is
insulated, and the magnetic field is switched off,
increasing the heat capacity of the refrigerant, thus
decreasing its temperature below the temperature of
the He heat sink. In practice, the magnetic field is
decreased slowly in order to provide continuous
cooling and keep the sample at an approximately
constant low temperature. Once the field falls to zero
(or to some low limiting value determined by the
properties of the refrigerant), the cooling power of
the ADR vanishes, and heat leaks will cause the
refrigerant to warm up.

Working Materials
The magnetocaloric 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; it can be substantial for normal
ferromagnets which undergo a second order magnetic
transition; and it is generally the largest for a
ferromagnet which undergoes a first order magnetic
transition.Also, crystalline electric fields and pressure
can have a substantial influence on magnetic entropy
and adiabatic temperature changes. 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 magnetocaloric
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

Paramagnetic Salts
The originally suggested refrigerant was a
paramagnetic salt, such as cerium magnesium nitrate.
The active magnetic dipoles in this case are those of
the electron shells of the paramagnetic atoms. In a
paramagnetic salt ADR, the heat sink is usually
provided by a pumped4He (about 1.2 K) or3He
(about 0.3 K) cryostat. An easily attainable 1 tesla
magnetic field is generally required for the initial
magnetization. The minimum temperature attainable
is determined by the self-magnetization tendencies of
the chosen refrigerant salt, but temperatures from 1 to
100 mK are accessible. Dilution refrigerators had for
many years supplanted paramagnetic saltADRs, but
interest in space-based and simple to use lab-ADRs
has recently revived the field. Eventually
paramagnetic salts become either diamagnetic or
ferromagnetic, limiting the lowest temperature which
can be reached using this method.

Nuclear Demagnetisation
One variant of adiabatic demagnetization that
continues to find substantial research application is
nuclear demagnetization refrigeration (NDR). NDR
follows the same principle described above, but in
this case the cooling power arises from the magnetic
dipoles of the nuclei of the refrigerant atoms, rather
than their electron configurations. Since these dipoles are of much smaller magnitude, they are less prone to
self-alignment and have lower intrinsic minimum
fields. This allows NDR to cool the nuclear spin
system to very low temperatures, often 1 µK or
below. Unfortunately, the small magnitudes of
nuclear magnetic dipoles also make them less
inclined to align to external fields. Magnetic fields of
3 teslas or greater are often needed for the initial
magnetization step of NDR.In NDR systems, the
initial heat sink must sit at very low temperatures
(10–100 mK). This precooling is often provided by
the mixing chamber of a dilution refrigerator or a
paramagnetic salt ADR stage.
16-03-2011, 09:27 AM
Post: #24
RE: magnetic refrigeration full report

.doc  reportmagnet.doc (Size: 51 KB / Downloads: 143)
CHAPTER-1
INTRODUCTION

Magnetic refrigeration is a cooling technology based on the magneto caloric 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. 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-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).
2.1 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 magneto caloric 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 (PrNi5) 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
CHAPTER-
CONSTRUCTION AND WORKING
3.1 COMPONENTS REQUIRED

1. Magnets
2. Hot Heat exchanger
3. Cold Heat Exchanger
4. Drive
5. Magneto caloric wheel
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.
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.
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.
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.
3.2 WORKING PRINCIPLE
As shown in the figure 3.2.1, 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
Fig 3.2.1 Principle
3.3 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.
Fig 3.3.1. Working
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). Energy (and entropy) transfers from thermal entropy to magnetic entropy (disorder of the magnetic dipoles).
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 (+Q). Once the refrigerant and refrigerated environment is in thermal equilibrium, the cycle begins a new one.
3.4 PROPER FUNCTIONING
The place we want to cool it, we will apply magnetic field to the material in that place and as its temperature increases, it will absorb heat from that place and by taking the magnetic material outside in the surroundings, we will remove the magnetic material from magnetic field and thus it will loose heat as its temperature decreases and hence the cycle repeats over and again to provide the cooling effect at the desired place.
3.4.1. WORKING MATERIALS
The magnetocaloric 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; it can be substantial for normal ferromagnets which undergo a second order magnetic transition; and it is generally the largest for a ferromagnet which undergoes a first order magnetic transition.
Also, crystalline electric fields and pressure can have a substantial influence on magnetic entropy and adiabatic temperature changes.
Currently, alloys of gadolinium producing 3 to 4 K per tesla (K/T) 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 magnetocaloric 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.
CHAPTER-
REQUIREMENTS FOR PRATICAL APPLICATIONS
4.1 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.
4.2 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:
(a) Tubes
(b) Perforated plates
© Wire screens
(d) Particle beds
4.3 SUPER CONDUCTING MAGNETS
Most practical magnetic refrigerators are based on superconducting magnets operating at cryogenic temperatures (i.e., at -269 C or 4 K).These devices are electromagnets that conduct electricity with essentially no resistive losses. The superconducting wire most commonly used is made of a Niobium-Titanium alloy.
Only superconducting magnets can provide sufficiently strong magnetic fields for most refrigeration applications. A typical field strength is 8 Tesla (approximately 150,000 times the Earth's magnetic field).An 8 Tesla field can produce a magneto caloric temperature change of up to 15 C in some rare-earth materials.
4.4Active Magnetic Regenerators (AMR's)
A regenerator that undergoes cyclic heat transfer operations and the magneto caloric effect is called an Active Magnetic Regenerator (AMR).An AMR should be designed to possess the following attributes:
These requirements are often contradictory, making AMR's difficult to design and fabricate.
1. High heat transfer rate
2. Low pressure drop of the heat transfer fluid
3. High magneto caloric effect
4. Sufficient structural integrity
5. Low thermal conduction in the direction of fluid flow
6. Low porosity
7. Affordable materials
8. Ease of manufacture
01-04-2011, 12:53 PM
Post: #25
RE: magnetic refrigeration full report

.doc  47093713-30733590-Magnetic-Refrigeration.doc (Size: 102.72 KB / Downloads: 107)
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
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