Magnetic Cooling New

8/8/2019 Magnetic Cooling New

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[MAGNETIC COOLING] 0821216050

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CONTENTS

1. Acknowledgement

2. Introduction

3. Objectives

4. Components

5. Working

6. Benifits

7. Activties

8. Magnetic materials

9. R egener ators

10. Superconducting magnets

11. Active magnetic regener ators(AMR¶s)

12. A rotary AMR liquefier

13. Comparison




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MAGNETIC COOLING

Introduction

Magnetic cooling is a freezing technology based on the

magneto caloric effect. This technique can be used to attain

extremely low temper atures (well below 1 kelvin), as well as the

r anges used in common refriger ators, depending on the design of

the system.

History

The effect was discovered in pure iron in 1881 by E. War burg.

Originally, the cooling effect varied between 0.5 to 2 K/T.

Major advances first a ppeared in the late 1920s when cooling via adiabatic demagnetization was independently proposed by two

Scientists: De bye (1926) and Giauque (1927).

The process was demonstr ated a few years later when Giauque and

MacDougall in 1933 used it to reach a temper ature of 0.25 K .

Between 1933 and 1997, a num ber of advances in utilization of the

MCE for cooling occurred.

This cooling technology was first demonstr ated experimentally by

Chemist No bel Laureate William F. Giauque and his colleague Dr .




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D.P. MacDougall in 1933 for cryogenic purposes (they reached

0.25 K)

Between 1933 and 1997, a num ber of advances occurred which ha

-ve been descri bed in some reviews.

In 1997, the first near room temper ature proof of concept magnetic

refriger ator was demonstr ated by Prof . K arl A. Gschneidner, Jr . by

the Iowa State University at Ames Labor atory. This event attr acted

interest from scientists and companies worldwide who started

developing new kinds of room temper ature materials and magnetic

refriger ator designs.

R efriger ators based on the magneto caloric effect have been

demonstr ated in labor atories, 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).




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MAGNETO CALORIC EFFECT

The Magneto caloric effect (MCE, from magnet and calorie) is

a Magneto-thermodynamic phenomenon in which a

reversi blechange in temper ature of a suitable material is caused

by exposingthe material to a changing magnetic field. This is

also known asadiabatic demagnetization by low temper ature

physicists, due tothe a pplication of the process specifically to

effect a temper aturedrop. In that part of the over allrefriger ation process, a decrease inthe strength of an externally

a pplied magnetic field allows themagnetic domains of a

chosen (magneto caloric) material to become disoriented from

the magnetic field by the agitating actionof the thermal energy

(phonons) present in the material. If thematerial is isolated so

that no energy is allowed to (e) migr ate intothe material during

this time (i.e. An adiabatic process), thetemper ature drops

as the domains absor b the thermal energy to perform their

reorientation. The r andomization of the domainsoccurs in a

similar f ashion to the r andomization at the curie temper ature,

except that magnetic dipoles overcome a decreasingexternal

magnetic field while energy remains constant, instead

ofmagnetic domains being disrupted from internal

ferromagnetism as energy is added.




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One of the most notable examples of the magneto caloric effect

is in the chemical element gadolinium and some of its

alloys.Gadolinium's temper ature is o bserved to increase when

it enters certain magnetic fields. When it leaves the magnetic

field, thetemper ature returns to normal. The effect is consider ably

stronger for the gadolinium alloy Gd5(Si

2Ge

2). Pr aseodymium

alloyed with nickel (Pr 5) has such a strong magneto caloric

effect that it has allowed scientists to a pproach within one

thousandth of a degree of absolute zero.

Magnetic R efriger ation is also called as

Adiabatic

Magnetization.




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OBJECTIVES

To develop more efficient and cost effective smascale

H2 liquefiers as an alternative to va por-compression cycles using

mag-netic refriger ation.

With the help of magnetic refriger ation our o bjective is

to solve the pro blem of hydrogen stor age as it ignites on a very low

temper ature. Hydrogen R esearch Institute (HRI) is studying it

with the help of magnetic refriger ation. We provide the cooling

for the hydrogen stor age by liquefying it.

The hydrogen can be liquefied at a low temper atur andthe low temper ature is achieved with the help of magnetic

refriger ation.

Thus, the magnetic refriger ation also provides a method

to store hydrogen by liquefying it. The term used for such a

device is magnetic liquefier .




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COMPONENTS

1. Magnets

2. Hot Heat exchanger

3. Cold Heat Exchanger

4. Drive

5. Magneto caloric wheel




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1. Magnets : - Magnets are the main functioning element of

the magnetic refriger ation.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

absor bs the heat from the material used and gives off to

the surrounding. It makes the tr ansfer of heat much

effective.

3. Cold Heat Exchanger :-The cold heat

exchanger absor bs 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.




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WORKING

The magnetic refriger ation is mainly based on magneto Caloric effect

according to which some materials change in temper ature when they are

magnetized and demagnetized.

Near the phase tr ansition of the magnetic materials, the adiabatic a pplication

of a magnetic field reduces the magnetic entropy by ordering the magnetic

moments. This results in a temper ature increase of the magnetic material. This

phenmenonis pr actically reversi ble for some magnetic materials; thus,

adiabatic removal of the field reverts the magnetic entropy to its original

state and cools the materialaccordingly. This reversi bility com bined with the

ability to create devices with inherent work recovery,makes magnetic

refriger ation a potential -ly more efficien process than gas compression

and expansion.

The efficiency of magnetic refriger ation can be as much as 50% greater than

for conventional refriger ators




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The process is performed as refrigeration

Cycle, analogous to the Carnot cycle, and

Can be described at a starting point

where by the chosen working su bstance

is introduced into a magnetic field (i.e.

the magnetic flux density is

increased).The working material is the

refriger ant, and starts in

thermalequili brium with the refriger ated

environment.

Adiabatic magnetization:The su bstance is placed in an insulated

environment. The increasing external magnetic field (+H) causes the

magnetic dipoles of the atoms to align, there by decreasing the

material's magnetic entropy and heatca pacity Since over all energy is

not lost (yet) and therefore total entropy is not reduced (according tothermodynamic laws), the net result is that the item heats up (T + Tad

).

Decreasing the material's magneticentropy and heat

ca pacity.Sinceover all energy is not lost (yet) and therefore total




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entropy is not reduced (according to thermodynamic laws), the net

result is that the item heats up (T + Tad).

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

reabsor bing he heat. Once sufficiently cooled, the

magnetocaloric material and the coolant are separ ated (H=0).

Adiabatic demagnetization:The su bstance is returned to another

adiabatic(insulated)condition so the total entropy remains constant.

However, this time the magnetic field

isdecreased,thethermalenergycauses the domains to overcome the

field, and thus the sample cools(i.e.an adiabatic temper ature change).

Energy(and entropy) tr ansfers from thermal entropy to magneticentropy (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 refriger ated. Because

The working material is cooler than the refriger ated environment( by

design), heat energy migr ates into the working material(+q).Once the

refriger ant and refriger ated environment are in thermal

equili brium,the cycle begins a new




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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 temper ature as the temper ature of it increases.

But on the other side when the magnetic material is

removed from the magnetic field, the thermometer shows low

temper ature as its temper ature decreases.




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PROPER FUNCTIONING

The place we want to cool it, we will a pply magnetic fieldto the material in that place and as its temper ature increases, it

will absor b 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 temper ature decreases and hence the cycle repeats over

and again to provide the cooling effect at the desired place.




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BENEFITS

TECHNICAL

1. HIGH EFFICIENCY : -As the magneto caloric effect is

highly reversi ble, the thermo dynamic efficiency of the

magnetic refriger ator is high.

It is some what 50% more than Va por Compression

cycle.

2. REDUCED COST : - As it eliminates the most in efficient part

of today¶s refriger ator i.e. comp. The cost reduces as a result.

3. COMPACTNESS : - It is possi ble to achieve high

energy density compact device. It is due to the reason that in case of

magnetic refriger ation the working su bstance is a social material (say

gadolinium) and not a gas as in case of va por 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.




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BENEFITS

SOCIO-ECONOM

IC

1. Competition in global market :- R esearch in

this field will provide the opportunity so that new

industries can be set up which may be ca pable of

competing the glo bal 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 ca pital cost of the equipment.

3. Key factor to new technologies :-If the

tr aining and hard wares are developed in this field they

will be the key f actor for new emerging technologies in

this world.




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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 refriger ators with the help

of some other refriger ants so that large magneto caloric effect

can be produced. This research work is under consider ation. We

are trying to find the refriger ant element which can produce theoptimum refriger ation effect.

2.Performance simulations of magnetic refrigerants:-Under

the research we are studying the performance of various

refriger ants and trying to simulate them. This will help us to

develop the technology the most and at a f aster r ate.

3.Design of a magnetic liquefier:- The stor age of hydrogen is

also a big pro blem. The magnetic liquefier developed so

f ar solves this pro blem.The magnetic liquefier is a device

based on magnetic refriger ation which help us to store thehydrogen at a low temper ature and after that it can be

used for various purposes.




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MAGNETIC REFRIGERATION PROCESS:

1 2 3 4 5

1: Sample at ambient temperature and magnetically disordered

2: Sample or dersinapplied magnetic Field: Magnetic Entropy (SM)

decreases forcing other types of entropy to increase, and causing the

sample to heatup.

3: Convective cooling process (forced air or liquid).

4: Sample at ambient temperature but magnetically ordered .

5: Sample removed from applied field, disordered, cooler than ambient.




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Regenerators

Magnetic refriger ation requires excellent heat tr ansfer to and from thesolid magnetic material. Efficient heat tr ansfer requires the largesurf ace areas

offered by porous materials. When these porous solids are used in

refriger ators, they are referred to as "regener ators´. Typical regener ator

geometries include:

(a)Tu bes

( b) Perfor ated plates

(c) Wire screens

(d) Particle beds




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Super Conducting Magnets

Most pr actical magnetic refriger ators are based on

superconducting magnets oper ating at cryogenic temper atures

(i.e., at -269 C or 4 K).These devices are electromagnets that

conduct electricity with essentially no resistive

losses.Theuperconducting wire most commonlyused is made of a

Nio bium-Titanium alloy.

Only superconducting magnets can provide

sufficiently strong magnetic fields for most refriger ation

a pplications.

A typical field strength is 8 Tesla (a pproximately 150,000 times

the Earth's magnetic field). An 8 Tesla field can produce a

magneto caloric temper ature change of up to 15 C in some

r are-earth materials.




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ActiveMagnetic Regenerators (AMR's)

A regener ator that undergoes cyclic heat tr ansfer oper ationsand the

magneto caloric effect is called an Active Magnetic R egener ator

(AMR ). An AMR should be designed to possess the following

attri butes:

These requirements are often contr adictory,

making AMR 's difficult to design and f abricate.

1. High heat tr ansfer r ate

2. Low pressure drop of the heat tr ansfer fluid

3. High magneto caloric effect

4. Sufficient structur al integrity

5. Low thermal conduction in the direction of fluid flow

6. Low porosity

7. Affordable materials

8. Ease of manuf acture




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A Rotary AMR Liquefier

The Cryofuel Systems Group at UVic is developing anAMR refriger ator for the purpose of liquefying natur al gas. A

rotary configur ation is used to move magnetic material into and

out of a superconducting magnet.

This technology can also be extended to the

liquef action of hydrogen.




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COMPARISON

The magneto caloric effect can be utilized in a

thermodynamic cycle to produce refriger ation. Such a

cycle is analogous to conventional gas-compression

refriger ation:




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The added advantages of MR over Gas Compression

R efriger ator are compactness, and higher reliability due to

Solid working materials instead of a gas, and fewer and much

slower moving partsour work in this field is geared toward the

development of magnetic alloys with MCEs, and phase

tr ansitions temper atures suitable for hydrogen liquef action from

R oom temper ature down to 20 K .

We are also collabor ating with The University of

Victoria (British Colum bia, Canada), on the development of

an experimental system to prove the technology




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ADVANTAGESOVER VAPOUR COMPRESSION

CYCLES:-

Magnetic refriger ation performs essentially the same task

as tr aditional compression-cycle gas refriger ation technology.

Heat and cold are not different qualities; cold is merely the

relative absence of heat. In both technologies, cooling is the

su btr action of heat from one place (the Interior of a home

refriger ator is one commonplace example) and the dumping of

that heat another place (a home refriger ator releases its heat

into the surrounding air). As more and more heat is su btr acted

from this target, cooling occurs. Tr aditional refriger ation

systems - whether air conditioning, freezers or other forms -

use gases that are alternately expanded and compressed to

perform the tr ansfer of heat. Magnetic refriger ation systems do

the same jo b, but with metallic compounds, not gases.

Compounds of the element gadoliniumare most commonly

used in magnetic refriger ation, although other compounds can

also be used.

Magnetic refriger ation is seen as an environmentally

friendly alternative to conventional va por-cycle refriger ation.

And as it eliminates the need for the most inefficient part of

today's




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refriger ators, the compressor, it should save costs. New

materials descri bed in this issue may bring pr actical magneto

caloric cooling a step closer . A large magnetic entropy change

has been found to occur in MnFeP0.45As

0.55 at room

temper ature, making it an attr active candidate for

commercial a pplications in magnetic refriger ation.

CONCLUSION

Last but not the least in my concluding words .I want to say that

magnetic cooling/refrigeration is the most efficient &eco friendly

invention in this modern era.

Magnetic refrigerator is best suitable refrigerator compare toother.

Magnetic refrigerator is the one of the revolutionary attempt in

the field of cooling.

As per the above data presented we came to conclusion that it can

produce cooling up to less than 1kelvin




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Magnetic Cooling New