Magnetic Refrigeration Seminar Report

A Seminar Report On

“MAGNETIC REFRIGERATION” Submitted in partial fulfillment for the award of the degree of

Bachelor of Technology in

Mechanical Engineering From

RAJASTHAN TECHNICAL UNIVERSITY, KOTA

Session 2009-13

Guided By: -

Submitted By: -

Mr. Narayan Lal Jain

Aman Agrawal

Reader, Mech.Deptt.

B.Tech.,VIII Sem.

Vit (East), Jaipur

(09EVVME005) Mechanical Engg.

Submitted to-

DEPARTMENT OF MECHANICAL ENGINEERING

VIVEKANANDA INSTITUTE OF TECHNOLOGY (EAST) VIT Campus, NRI Road, Jagatpura, Jaipur (Raj.)-303012

DEPARTMANT OF MECHNICAL ENGINEERING

VIVEKANANDA INSTITUTE OF TECHNOLOGY - EAST JAIPUR-303012

CERTIFICATE

This is to certify that the seminar entitled “Magnetic Refrigeration”, has been carried out by Aman agrawal under my guidance in partial fulfillment of the degree of bachelor of engineering in Mechanical Engineering of Rajasthan Technical University, Kota, during the academic session 2009 - 2013. To the best of my knowledge and belief this work has not been submitted elsewhere for the best award of any other degree. The work has been found satisfactory and is approved for submission.

GUIDE: (Sign by Guide)

(Sign by HOD)

Mr. Narayan Lal Jain

Mr. Rahul Goyal

Reader,

H.O.D

Deptt. of M.E.

Deptt. of M.E.

VIT - East, Jaipur

VIT - East, Jaipur

ACKNOWLEDGEMENT

I take this opportunity to express our deep sense of gratitude and respect towards our guide Mr. Narayan

Lal Jain, Department of Mechanical Engineering,

Vivekananda Institute of Technology – East, Jaipur. I am very much indebted to his for the generosity, expertise and guidance; I have received from him while collecting data on this seminar and throughout our studies. Without his support and timely guidance, the completion of my seminar would have seemed a far fetched dream. In this respect I find ourselves lucky to have his as our guide. He has guided us not only with the subject matter, but also taught us the proper style and technique of working and presentation. It is a great pleasure for me to express my gratitude towards those who are involved in the completion of my seminar report. I whole-heartedly thank to our HOD Mr. Rahul Goyal for their guidance. I am also indebted to all Sr. Engineers and others who gave me their valuable time and guidance. The various information and sources I used during my report completion find place in my report. I am also grateful to Senior Seminar Coordinators Mr. Satyesh Kr. Jha. .

Aman Agrawal IV year, VIII Sem (09EVVME005)

Deptt. Of Mechanical Engineering (Vit-east, Jaipur) 1

Magnetic Refrigeration

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.

Magnetic refrigeration is an emerging technology that exploits the magnetocaloric effect found in solid state refrigerants. The combination of solid-state refrigerants, water based heat transfer fluids and high efficiency leads to environmentally desirable products with minimal contribution to global warming. Among the numerous application of refrigeration technology air conditioning applications provide the largest aggregate cooling power and use of the greatest quantity of electric energy.



TABLE

1.INTRODUCTION ...................................................................................................................7 2. HISTORY ...............................................................................................................................8 3.REFRIGERATION .................................................................................................................9 3.1 Unit of Refrigeration:- ................................................................................................................. 9

4. METHODS OF REFRIGERATION ....................................................................................10 4.1 Non-cyclic refrigeration:- .......................................................................................................... 10 4.2 Cyclic refrigeration:- ................................................................................................................. 10 4.2.1 Vapour Cycle Refrigeration:- ............................................................................................................... 11 4.2.2 Gas cycle : - ........................................................................................................................................ 14

4.3 Thermoelectric refrigeration : -................................................................................................. 15 4.4 Magnetic refrigeration :- ........................................................................................................... 17 4.5 Other methods : - ....................................................................................................................... 17

5. OZONE LAYER DEPLETION ............................................................................................18 6. OBJECTIVES OF MAGNETIC REFRIGERATION ..........................................................19 7. MAGNETO CALORIC EFFECT ........................................................................................20 8. WORKING PRINCIPLE ......................................................................................................21 9.WORKING OF MAGNETIC REFRIGERATION SYSTEM ................................................22 9.1 Magnetic Refrigeration system : - ............................................................................................. 22 9.2 Refrigerator Configuration :- ................................................................................................... 23

10. MAGNETIC REFRIGERATION CYCLE .........................................................................25 10.1 Adiabatic Magnetization :- ...................................................................................................... 26 10.2 Isomagnetic Enthalpy Transfer :- ........................................................................................... 27 10.3 Adiabatic demagnetization :- ................................................................................................... 27 10.4 Isomagnetic Entropic Transfer :- ........................................................................................... 27

11. COMPARISON BETWEEN MAGNETIC REFRIGERATION AND CONVENTIONAL REFRIGERATION ..................................................................................................................28 12. COMPONENTS .................................................................................................................30 Deptt. Of Mechanical Engineering (Vit-east, Jaipur) 3


13. REQUIREMENTS FOR PRATICAL APPLICATIONS ....................................................32 13.1 Magnetic Materials : - .............................................................................................................. 32 13.2 Regenerators :- ......................................................................................................................... 34 13.3 Super Conducting Magnets :- .................................................................................................. 35 13.4 Active Magnetic Regenerators (AMR's) :- .............................................................................. 36

14. APPLICATIONS ................................................................................................................38 14.1 A rotary AMR liquefier :- ........................................................................................................ 38 14.2 Future Applications:- ............................................................................................................... 39

15. BENEFITS .........................................................................................................................40 15.1 TECHNICAL :- ...................................................................................................................... 40 15.2 SOCIO-ECONOMIC :- ........................................................................................................... 40

16. ADVANTAGES .....................................................................................................................41 16.1 Advantages over Vapour compression and Vapour absorption Cycles :- ............................. 41 16.2 Potential Advantages : - ........................................................................................................... 42

17. DISADVANTAGES ............................................................................................................43 18. CURRENT AND FUTURE USES .....................................................................................44 19. CASE STUDY.....................................................................................................................45 20. CONCLUSION ...................................................................................................................46 21. REFERENCES ..................................................................................................................47



FIGURE INDEX

Fig. 1: Vapor compression refrigeration…………………………………………………….....12 Fig. 2: Temperature–Entropy diagram……………………………………………………….....12 Fig. 3: Vapor absorption cycle……………………………………………………….……. … 13 Fig. 4: Gas cycle……………………………………………………………………….…….… 15 ..

Fig. 5: Thermoelectric Refrigeration…………………………………………………..….…… 16 ..

Fig. 6: Working Principle…………………………………………………………………...…. 21 Fig. 7: Flow process diagram (a)……………………………………………………….……... 22 Fig. 8: Flow process diagram(b)…………………………………………………….……..….. 23 Fig. 9: Magneto caloric Effect…………………………………………………….………..…. 25 Fig. 10: Magnetic Refrigeration cycle v/s Vapor Cycle Refrigeration ………………… ..……26 Fig. 11: Comparison between Magnetic Refrigeration and Conventional Refrigeration……...28 Fig. 12 : Refrigeration cycles for conventional gas compression and magnetic refrigeration...29 Fig. 13: Components…………………………………………………………………………... 30 Fig. 14: Magnetic Materials………………………………………………………………….... 33 Fig. 15: Regenerators………………………………………………………………………..… 35 Fig. 16: Super Conducting Magnets………………………………………………………...…. 36 ..

Fig. 17: A rotary AMR liquefier …………………………………………………………….....38



CONTENTS ACKNOWLEDGEMENT…………………………………….……………….…...I ABSTRACT………………………………………………………………………...II INDEX…………………………………………………………………....................III FIGURE INDEX…………………………………………………………………….IV

1.INTRODUCTION ............................................................................................................................... 7 2. HISTORY ........................................................................................................................................... 8 3.REFRIGERATION ............................................................................................................................. 9 4. METHODS OF REFRIGERATION ................................................................................................ 10 5. OZONE LAYER DEPLETION......................................................................................................... 18 6. OBJECTIVES OF MAGNETIC REFRIGERATION ...................................................................... 19 7. MAGNETO CALORIC EFFECT ..................................................................................................... 20 8. WORKING PRINCIPLE .................................................................................................................. 21 9.WORKING OF MAGNETIC REFRIGERATION SYSTEM............................................................. 22 10. MAGNETIC REFRIGERATION CYCLE ...................................................................................... 25 11. COMPARISON BETWEEN MAGNETIC REFRIGERATION AND CONVENTIONAL REFRIGERATION .............................................................................................................................. 28 12. COMPONENTS.............................................................................................................................. 30 13. REQUIREMENTS FOR PRATICAL APPLICATIONS ................................................................ 32 14. APPLICATIONS ............................................................................................................................ 38 15. BENEFITS ..................................................................................................................................... 40 16. ADVANTAGES .................................................................................................................................. 41 17. DISADVANTAGES ........................................................................................................................ 43 18. CURRENT AND FUTURE USES .................................................................................................. 44 19. CASE STUDY ................................................................................................................................. 45 20. CONCLUSION ............................................................................................................................... 46 21. REFERENCES............................................................................................................................... 47 Deptt. Of Mechanical Engineering (Vit-east, Jaipur) 6


1

1. INTRODUCTION

Refrigeration is the process of removing heat from matter which may be a solid, a liquid, or a gas. Removing heatfrom the matter cools it, or lowers its temperature. In the mechanical refrigeration a refrigerant is a substance capable of transferring heat that it absorbs at low temperatures and pressures to a condensing medium; inthe region of transfer, the refrigerant is at higher temperatures and pressures. By means of expansion, compression, and a cooling medium, such as air or water, the refrigerant removes heat from a substance andtransfers it to the cooling medium.

Our society is highly dependent on reliable cooling technology. Refrigeration iscritical to our health and the global economy. Consumer application includes airconditioning, food preservation, air dehumidification, beverage dispensing and ice making without refrigeration the food supply wood still be seasonal and limited to locally produced non-perishable items.

Modern refrigeration is almost entirely based on a compression/ expansionrefrigeration cycle. It is a mature, reliable & relatively low cost technology. Over the years,all parts of a conventional refrigerator were considerably improved due to extendedresearch and development efforts. Furthermore, some liquids used as refrigerants arehazardous chemicals, while other eventually escape into the environment contributingtowards ozone layer depletion and global warming and therefore, conventionalrefrigeration ultimately promotes deleterious trends in the global climate.

Magnetic refrigerator, which has advantages in refrigeration efficiency, reliability, low noise and environmental friendliness with respect to the conventional gas refrigerators, is becoming a promising technology to replace the conventional technique. The development of the magnetic material, magnetic refrigeration cycles, magnetic field and therefrigerator of room temperature magnetic refrigeration is introduced.



2

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)

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 magneto caloric 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).



3

3.REFRIGERATION

Refrigeration is the process of removing heat from an enclosed space, or from a substance, and moving it to a place where it is unobjectionable. The primary purpose of refrigeration is lowering the temperature of the enclosed space or substance and then maintaining that lower temperature. The term cooing refers generally to any natural or artificial process by which heat is dissipated. The process of artificially producing extreme cold temperatures is referred to as cryogenics. Cold is the absence of heat, hence in order to decrease a temperature, one “removes heat", rather than "adding cold." In order to satisfy the Second Law of Thermodynamics, some form of work must be performed to accomplish this. This work is traditionally done by mechanical work but can also be done by magnetism, laser or other means.

3.1 Unit of Refrigeration:Domestic and commercial refrigerators may be rated in kJ/s, or Btu/h of cooling. Commercial refrigerators in the US are mostly rated in tons of refrigeration, but elsewhere in kW. One ton of refrigeration capacity can freeze one short ton of water at 0 °C (32 °F) in 24 hours. Based on that: Latent heat of ice (i.e., heat of fusion) = 333.55 kJ/kg ≈ 144 Btu/lb. One short ton = 2000 lb Heat extracted = (2000) (144)/24 hr. = 288000 Btu/24 hr. = 12000 Btu/hr. =200 Btu/min1 ton refrigeration = 200 Btu/min = 3.517 kJ/s = 3.517kW A much less common definition is: 1 tonne of refrigeration is the rate of heat removal required to freeze a metric ton (i.e., 1000 kg) of water at 0°Cin 24 hours. Based on the heat of fusion being 333.55 kJ/kg, 1 ton of refrigeration = 13,898 kJ/h = 3.861 kW. Most residential air conditioning units range in capacity from about 1 to 5 tons of refrigeration.



4

4. METHODS OF REFRIGERATION Methods of refrigeration can be classified as non-cyclic, cyclic, thermoelectric and magnetic.

4.1 Non-cyclic refrigeration:In non-cyclic refrigeration, cooling is accomplished by melting ice or by subliming dry ice (frozen carbon dioxide). These methods are used for small-scale refrigeration such as in laboratories and workshops, or in portable coolers.

Ice owes its effectiveness as a cooling agent to its melting point of 0 °C (32 °F) at sea level. To melt, ice must absorb 333.55 kJ/kg (about 144 Btu/lb) of heat. Foodstuffs maintained near this temperature have an increased storage life.

Solid carbon dioxide has no liquid phase at normal atmospheric pressure, and sublimes directly from the solid to vapor phase at a temperature of -78.5 °C (-109.3 °F), and is effective for maintaining products at low temperatures during sublimation. Systems such as this where the refrigerant evaporates and is vented to the atmosphere are known as "total loss refrigeration".

4.2 Cyclic refrigeration:This consists of a refrigeration cycle, where heat is removed from a low-temperature space or source and rejected to a high-temperature sink with the help of external work, and its inverse, the thermodynamic power cycle. In the power cycle, heat is supplied from a high-temperature source to the engine, part of the heat being used to produce work and the rest being rejected to a low-temperature sink. This satisfies the second law of thermodynamics.

A refrigeration cycle describes the changes that take place in the refrigerant as it alternately absorbs and rejects heat as it circulates through a refrigerator. It is also applied Deptt. Of Mechanical Engineering (Vit-east, Jaipur) 10


to HVACR work, when describing the "process" of refrigerant flow through an HVACR unit, whether it is a packaged or split system.

Heat naturally flows from hot to cold. Work is applied to cool a living space or storage volume by pumping heat from a lower temperature heat source into a higher temperature heat sink. Insulation is used to reduce the work and energy needed to achieve and maintain a lower temperature in the cooled space. The operating principle of the refrigeration cycle was described mathematically beside in 1824 as a heat engine. The most common types of refrigeration systems use the reverse-Rankine vapor-compression refrigeration cycle, although absorption heat pumps are used in a minority of applications.

Cyclic refrigeration can be classified as: 1. Vapour cycle, and 2. Gas cycle

4.2.1 Vapour Cycle Refrigeration:-

Vapour cycle refrigeration can further be classified as: 1. Vapor-compression refrigeration 2. Vapor-absorption refrigeration

4.2.1.1 Vapor-compression refrigeration :

The vapour-compression cycle is used in most household refrigerators as well as in many large commercial and industrial refrigeration systems. Figure 1 provides a schematic diagram of the components of a typical vapor-compression refrigeration system.

The thermodynamics of the cycle can be analyzed on a diagram as shown in Figure 2. In this cycle, a circulating refrigerant such as Freon enters the compressor as a vapor. From point 1 to point 2, the vapor is compressed at constant entropy and exits the compressor as a vapor at a



higher temperature, but still below the vapor pressure at that temperature. From point 2 to point 3 and on to point 4, the vapor travels through the condenser which cools the vapor until it starts condensing, and then condenses the vapor into a liquid by removing additional heat at constant pressure and temperature. Between points 4 and 5, the liquid refrigerant goes through the expansion valve (also called a throttle valve) where its pressure abruptly decreases, causing flash and auto-refrigeration of, typically, less than half of the liquid.

Figure 1: Vapor compression refrigeration

Figure 2: Temperature–Entropy diagram



That results in a mixture of liquid and vapor at a lower temperature and pressure as shown at point 5. The cold liquid-vapor mixture then travels through the evaporator coil or tubes and is completely vaporized by cooling the warm air (from the space being refrigerated) being blown by a fan across the evaporator coil or tubes. The resulting refrigerant vapor returns to the compressor inlet at point 1 to complete the thermodynamic cycle. The above discussion is based on the ideal vapor-compression refrigeration cycle, and does not take into account real-world effects like frictional pressure drop in the system, slight thermodynamic irreversibility during the compression of the refrigerant vapor, or non-ideal gas behavior (if any).

4.2.1.2 Vapor absorption cycle:In the early years of the twentieth century, the vapor absorption cycle using water-ammonia systems was popular and widely used. After the development of the vapor compression cycle, the vapor absorption cycle lost much of its importance because of its low coefficient of performance (about one fifth of that of the vapor compression cycle). Today, the vapor absorption cycle is used mainly where fuel for heating is available but electricity is not, such as in recreational vehicles that carry LP gas. It is also used in industrial environments where plentiful waste heat overcomes its inefficiency.

Figure 3: Vapor absorption cycle



The absorption cycle is similar to the compression cycle, except for the method of raising the pressure of the refrigerant vapor. In the absorption system, the compressor is replaced by an absorber which dissolves the refrigerant in a suitable liquid, a liquid pump which raises the pressure and a generator which, on heat addition, drives off the refrigerant vapor from the highpressure liquid. Some work is needed by the liquid pump but, for a given quantity of refrigerant, it is much smaller than needed by the compressor in the vapor compression cycle. In an absorption refrigerator, a suitable combination of refrigerant and absorbent is used. The most common combinations are ammonia (refrigerant) with water (absorbent), and water (refrigerant) with lithium bromide (absorbent).

4.2.2 Gas cycle : -

When the working fluid is a gas that is compressed and expanded but doesn't change phase, the refrigeration cycle is called a gas cycle. Air is most often this working fluid. As there is no condensation and evaporation intended in a gas cycle, components corresponding to the condenser and evaporator in a vapor compression cycle are the hot and cold gas-to-gas heat exchangers in gas cycles.

The gas cycle is less efficient than the vapor compression cycle because the gas cycle works on the reverse Brayton cycle instead of the reverse Rankine cycle. As such the working fluid does not receive and reject heat at constant temperature. In the gas cycle, the refrigeration effect is equal to the product of the specific heat of the gas and the rise in temperature of the gas in the low temperature side. Therefore, for the same cooling load, a gas refrigeration cycle needs a large mass flow rate and is bulky.

Because of their lower efficiency and larger bulk, air cycle coolers are not often used nowadays in terrestrial cooling devices. However, the air cycle machine is very common on gas turbine-powered jet aircraft as cooling and ventilation units, because compressed air is readily available from the engines' compressor sections. Such units also serve the purpose of pressurizing the aircraft.



Figure 4: Gas cycle

A schematic diagram of an air refrigeration system working on a simple gas cycle is shown below. In this arrangement, the compressor and the expander are shown coupled together since the expander work is utilized to provide a part of the compressor work. Point 4 in the figure represents the state of the refrigerated air, which would absorb heat at a constant pressure until it attains the temperature corresponding to point 1. At 1, the air is isentropically compressed to 2, after which it is cooled at constant pressure to 3. The cooling medium is invariably the surrounding atmospheric air as the cycle is presently employed only in aircraft refrigeration. The air is finally expanded isentropically to 4 whereby it gets cooled. In this system other gases like Hydrogen, Carbon-di-oxide and Hydrocarbon gases can also be used, instead of air.

4.3 Thermoelectric refrigeration : Thermoelectric cooling uses the Peltier effect to create a heat flux between the junction of two different types of materials. A Peltier cooler, heater, or thermoelectric heat pump is a solid-state active heat pump which transfers heat from one side of the device to the other, with consumption of electrical energy, depending on the direction of the current. Such an instrument is also called a Peltier device, Peltier heat pump, solid state refrigerator, or thermoelectric cooler (TEC). They



can be used either for heating or for cooling (refrigeration), although in practice the main application is cooling. It can also be used as a temperature controller that either heats or cools. [1]

This technology is far less commonly applied to refrigeration than vapor-compression refrigeration is. The main advantages of a Peltier cooler (compared to a vapor-compression refrigerator) are its lack of moving parts or circulating liquid, and its small size and flexible shape (form factor). Its main disadvantage is high cost and poor power efficiency. Many researchers and companies are trying to develop Peltier coolers that are both cheap and efficient.

Figure 5: Thermoelectric Refrigeration

A Peltier cooler can also be used as a thermoelectric generator. When operated as a cooler, a voltage is applied across the device, and as a result, a difference in temperature will build up between the two sides.[2] When operated as a generator, one side of the device is heated to a temperature greater than the other side, and as a result, a difference in voltage will build up between the two sides (the Seebeck effect). However, a well-designed Peltier cooler will be a mediocre thermoelectric generator and vice-versa, due to different design and packaging requirements.



4.4 Magnetic refrigeration :Magnetic refrigeration, or adiabatic demagnetization, is a cooling technology based on the magneto caloric effect, an intrinsic property of magnetic solids. The refrigerant is often 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.

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. A 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. This increases the heat capacity of the refrigerant, thus decreasing its temperature below the temperature of the heat sink.

Because few materials exhibit the needed properties at room temperature, applications have so far been limited to cryogenics and research.

4.5 Other methods : -

Other methods of refrigeration include the air cycle machine used in aircraft; the vortex tube used for spot

cooling, when compressed air

is available; and thermoacoustic

refrigeration using sound waves in a pressurized gas to drive heat transfer and heat exchange; steam jet cooling popular in the early 1930s for air conditioning large buildings; thermo elastic cooling using a smart metal alloy stretching and relaxing. Many Stirling cycle heat engines can be run backwards to act as a refrigerator, and therefore these engines have a niche use in cryogenics. In addition there are other types of cryocoolers such as Gifford-McMahon coolers, Joule-Thomson coolers, pulse-tube refrigerators and, for temperatures between 2 mK and 500 mK, dilution refrigerators.



5

5. OZONE LAYER DEPLETION

Ozone depletion describes two distinct but related phenomena observed since the late 1970s: a steady decline of about

4% per decade in the total volume of ozone in Earth's

stratosphere (the ozone layer), and a much larger springtime decrease in stratospheric ozone over Earth's polar regions. The latter phenomenon is referred to as the ozone hole. In addition to these well-known stratospheric phenomena, there are also springtime polartropospheric ozone depletion events.

The main source of these halogen atoms in the stratosphere is photo dissociation of manmade halocarbon refrigerants (CFCs, freons, halons). These compounds are transported into the stratosphere after being emitted at the surface.[2] Both types of ozone depletion were observed to increase as emissions of halo-carbons increased.

CFCs and other contributory substances are referred to as ozone-depleting substances (ODS). Since the ozone layer prevents most harmful UVB wavelengths (280–315 nm) of ultraviolet light (UV light) from passing through the Earth's atmosphere, observed and projected

decreases in ozone have generated worldwide concern leading to adoption of the Montreal Protocol that bans the production of CFCs, halons, and other ozone-depleting chemicals such as carbon tetrachloride and trichloroethane. It is suspected that a variety of biological consequences such as increases in skin cancer, cataracts,[3] damage to plants, and reduction of plankton populations in the ocean's photic zone may result from the increased UV exposure due to ozone depletion. An international agreement – Montreal Protocol was signed by all countries in order to prevent further depletion of the Ozone layer. According to this international agreement, the use of fully halogenated CFC’s, like R11, R12, R13, R14 and R5O2, was phased out by 2000 AD.



6

6. OBJECTIVES OF MAGNETIC REFRIGERATION

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.



7 7. 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 (magneto caloric) 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 (Pr Ni 5) has such a strong magneto caloric 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.



8 8. 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.

Figure 6: Working Principle 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 lose heat as its temperature decreases and hence the cycle repeats over and again to provide the cooling effect at the desired place.



9 9.WORKING OF MAGNETIC REFRIGERATION SYSTEM

9.1 Magnetic Refrigeration system : -

Consists of two beds containing spherical powder of Gadolinium with water being used as the heat transfer fluid. The magnetic field for this system is 5 Wb/m2, providing a temperature span of 38 K. The process flow diagram for the magnetic refrigeration system is shown in Figure-6.3.

Figure 7: Flow process diagram (a)

A mixture of water and ethanol serves as the heat transfer fluid for the system. The fluid first passes through the hot heat exchanger, which uses air to transfer heat to the atmosphere. The Deptt. Of Mechanical Engineering (Vit-east, Jaipur) 22


fluid then passes through the copper plates attached to the no magnetized cooler-magneto caloric beds and loses heat. A fan blows air over this cold fluid into the freezer to keep the freezer temperature at approximately 0°F. The heat transfer fluid then gets heated up to 80°F, as it passes through the copper plates adjoined by the magnetized warmer magneto caloric beds, where it continues to cycle around the loop. However, the magneto caloric beds simultaneously move up and down, into and out of the magnetic field. The second position of the beds is shown in Figure 6.4. The cold air from the freezer is blown into the refrigerator by the freezer fan shown in Figure 6.5. The temperature of the refrigerator section is kept around 39°F.

9.2 Refrigerator Configuration :The typical household refrigerator has an internal volume of 165-200 litres, where the freezer represents approximately 30% of this volume. Freezers are designed to maintain a temperature of 0°F. Refrigerators maintain a temperature of 39°F. The refrigerator will be insulated with polyurethane foam, one of the most common forms of insulation available. The refrigerator is kept cool by forcing cold air from the freezer into the refrigerator by using a small fan.

Figure 8: Flow process diagram(b) The control system for maintaining the desired internal temperatures consists of two thermostats with on/off switches. The freezer thermostat regulates the temperature by turning the Deptt. Of Mechanical Engineering (Vit-east, Jaipur) 23


compressor off when the temperature gets below 0°F. A second thermostat regulates the fan that cools the refrigerator to 39°F. To maintain a frost-free environment in the freezer, a defrost timer will send power to a defrost heater on the coils for a fifteen minute time period every eight hours. In the first six minutes, the walls of the freezer will be defrosted. The water will then drain into a pan at the base of the refrigerator. The next nine minutes involve the safety factor of not reaching a temperature in the freezer that is too high. Also, a safety thermostat keeps the liquid water from freezing as it drains.

The heat transfer fluid for the magnetic refrigeration system is a liquid alcohol water mixture. The mixture used in the design consists of 60 % ethanol and 40 % water. This mixture has a freezing point of –40°F, assuring that the mixture does not freeze at operating temperatures. This heat transfer fluid is cheaper than traditional refrigerants and also eliminates the environmental damage produced from these refrigerants. The temperature of the fluid in the cycle is in the range of –12°F to 80°F. The heat transfer fluid, at approximately 70°F, gets cooled to –12°F by the non-magnetized cold set of beds. This cooled fluid is then sent to the cold heat exchanger, where it absorbs the 15 excess heats from the freezer. This fluid leaves the freezer at 0°F. The warm fluid then flows through the opposite magnetized set of beds, where it is heated up to 80°F. This hot stream is now cooled by air at room temperature in the hot heat exchanger to 70°F. The cycle then repeats itself every three seconds after the beds have switched positions. Copper tubing is used throughout the loop and in the two heat exchangers. The two sets of beds contain the small spheres of magneto caloric material. The beds are alternated in and out of the magnetic field using a chain and sprocket drive shaft. The drive shaft rotates the beds back and forth while still keeping them in contact with the heat transfer plates.



10 10. MAGNETIC REFRIGERATION CYCLE

The magnetic refrigeration is mainly based on magneto caloric effect according to which Some materials change in temperature when they are magnetized and demagnetized.

Near the phase transition of the magnetic materials, the adiabatic application of a magnetic field reduces the magnetic entropy by ordering the magnetic moments. This results in a temperature increase of the magnetic material. This phenomenon is practically reversible for some magnetic materials; thus, adiabatic removal of the field revert the magnetic entropy to its original state and cools the material accordingly. This reversibility combined with the ability to create devices with inherent work recovery, makes magnetic refrigeration a potentially more efficient process than gas compression and expansion. The efficiency of magnetic refrigeration can be as much as 50% greater than for conventional refrigerators.

The process is performed as a refrigeration cycle, analogous to the Carnot cycle, and can be described as 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.

Figure 9: Magneto caloric Effect Deptt. Of Mechanical Engineering (Vit-east, Jaipur) 25


Figure 10: Magnetic Refrigeration cycle v/s Vapor Cycle Refrigeration Process is similar to gas compression and expansion cycle as used in regular refrigeration cycle.

Steps of thermodynamic Cycle:1. Adiabatic Magnetization 2.

Isomagnetic Enthalpy Transfer

3. Adiabatic demagnetization 4. Isomagnetic Entropic Transfer

10.1 Adiabatic Magnetization :-

In first step of cycle,  A magneto caloric Substance placed in an insulated environment. Deptt. Of Mechanical Engineering (Vit-east, Jaipur) 26


 Externally applied Magnetic field (+H) increased.  This 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). (ΔTad = adiabatic temperature variation)

10.2 Isomagnetic Enthalpy Transfer : Added heat can then be removed by a fluid like water or helium (-Q)  Magnetic Field held constant to prevent the dipoles from reabsorbing the heat.  After a sufficient cooling Magnetocalric material and coolant are separated(H=0)

10.3 Adiabatic demagnetization : Substance is returned to another adiabatic (insulated) condition.  So total Entropy remains constant.  Magnetic field is decreased (-H).  Thermal Energy causes the Magnetic moments to overcome the field and sample cools (adiabatic temperature change).  Energy transfers from thermal entropy to magnetic entropy (disorder of the magnetic dipoles).

10.4 Isomagnetic Entropic Transfer : Material is placed in thermal contact with the Environment being refrigerated.  Magnetic field held constant to prevent material from heating back up.  Because the working material is cooler than the refrigerated environment, heat energy migrates into the working material (+Q)  Once the refrigerant and refrigerated environment are in thermal equilibrium, the cycle continuous. Deptt. Of Mechanical Engineering (Vit-east, Jaipur) 27


11 11. COMPARISON BETWEEN MAGNETIC REFRIGERATION AND CONVENTIONAL REFRIGERATION

Figure 11: Comparison between Magnetic Refrigeration and Conventional Refrigeration

In Figure 2 the four basic steps of a conventional gascompression/ Expansion refrigeration process are shown. These are a compression of a gas, extraction of heat, Expansion of the gas, and injection of heat. The two Process steps extraction of heat and expansion are Responsible for a cooling process in two steps. The main Cooling usually occurs through the expansion of the gas.

The steps of a magnetic refrigeration process are Analogous. By comparing a with b, in Figure.2 one can see That instead of compression of a gas, a magnetocaloric Material is moved



into a magnetic field and that instead of Expansion it is moved out of the field. As explained in the Previous section, these processes change the temperature Of the material and heat may be extracted, respectively Injected just as in the conventional process. There are Some differences between the two processes. The heat Injection and rejection in a gaseous refrigerant is a rather Fast process, because turbulent motion transports heat Very fast. Unfortunately, this is not the case in the solid Magnetocaloric materials. Here, the transport mechanism For heat is slow molecular diffusion. Therefore, at present fi Ligree porous structures are considered to be the best Solution to overcome this problem. The small distances From the central regions of the material to an adjacent fluid Domain, where a heat transport fluid captures the heat and Transports it out of the material, are ideal to make the Magnetic cooling process faster. Furthermore, the not very Large adiabatic temperature differences of magnetocaloric Materials will require more often a design of cascade or Regenerative magnetic refrigerators than in conventional Refrigerators and hence require additional heat transfer Steps. In the Figure.2 (a) is the conventional gascompression Process is driven by continuously repeating The four different basic processes shown and (b) is the Magnetic refrigeration cycle comparison. Compression is Replaced by adiabatic magnetization and expansion by Adiabatic demagnetization.

(A)

(b)

Figure 12 : Refrigeration cycles for conventional gas compression and magnetic refrigeration



12

12. COMPONENTS Components required for construction :1. Magnets 2. Hot Heat exchanger 3. Cold Heat Exchanger 4. Drive 5. Magneto caloric wheel

Figure 13: Components



1. Magnets : Magnets are the main functioning element of the magnetic refrigeration. Magnets provide the magnetic field to the material so that they can lose 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.



13 13. REQUIREMENTS FOR PRATICAL APPLICATIONS There are some requirements for practical applications, those are :-

13.1 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 rareearth 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.

Figure 14: Magnetic Materials

Since Brown first applied ferromagnetic material gadolinium (Gd) in the room temperature magnetic refrigerator in 1976, the research range for magnetic refrigeration working materials has been greatly expanded. At first, some ferromagnets concerning the second order transition were investigated for the large MCE existing inthem. Recently the magnetic materials undergoing a firstorder magnetic transition become the focus after the giant MCE was found in GdSiGe alloys.



Some magnetic materials that are promise to be used in the future, the following list of promising categories of magnetocaloric materials for application in magnetic refrigerators: • binary and ternary intermetallic compounds • gadolinium-silicon-germanium compounds • manganites • lanthanum-iron based compounds • manganese-antimony arsenide • iron-manganese-arsenic phosphides • amorphous fine met-type alloys (very recent)

Gadolinium, a rare-earth metal, exhibits one of the largest known magneto caloric effects. It was used as the refrigerant for many of the early magnetic refrigeration designs. The problem with using pure gadolinium as the refrigerant material is that it does not exhibit a strong magneto caloric effect at room temperature. More recently, however, it has been discovered that arcmelted alloys of gadolinium, silicon, and germanium are more efficient at room temperature. The prototype magnetic material available for room temperature magnetic refrigeration is the lanthanide metal gadolinium (Gd). At the Curie temperature of 294 K, Gd undergoes a secondorder paramagnetic – ferromagnetic phase transition. The MCE and the heat capacity of Gd have been studied in many research activities. However, many urgent problems such as easy oxidation, hard preparation, and high price, need to be settled before they are applied in room temperature magnetic refrigeration.

13.2 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 Deptt. Of Mechanical Engineering (Vit-east, Jaipur) 34


(b) Perforated plates (c) Wire screens (d) Particle beds

Figure 15: Regenerators

13.3 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 Deptt. Of Mechanical Engineering (Vit-east, Jaipur) 35


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.

Figure 16: Super Conducting Magnets

13.4 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



14 14. APPLICATIONS

14.1 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.

Figure 17: A rotary AMR liquefier



14.2 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 used for 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



15

15. BENEFITS 15.1 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.

15.2 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



16 16. ADVANTAGES

16.1 Advantages over Vapour compression and Vapour absorption 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 common place 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.



16.2 Potential Advantages : The potential advantages of magnetic refrigeration bare valid in comparison with the direct evaporation refrigerating machines:

 Purchase cost

may be

high,

but

running

costs are 20%

less than the

conventional chillers.  Thus life cycle cost is much less.  Ozone depleting refrigerants are avoided in this system, hence it more

eco-friendly.

 Energy conservation and reducing the energy costs are added advantages.  The efficiency of magnetic refrigeration is 60% to 70% as compared to Carnot cycle.  Magnetic refrigeration is totally maintenance free & mechanically simple in construction.  “green” technology, no use of conventional refrigerants  Noise less technology (no compressor). This is an advantage in certain contexts such as medical applications  Higher energy efficiency. Thermodynamic cycles close to Carnot process are possible due to the reversibility of the MCE  Simple design of machines, e.g. Rotary porous heat exchanger refrigerator  Low (atmospheric) pressure. This is an advantage in certain applications such as in airconditioning and refrigeration units in automobiles.



17 17. DISADVANTAGES

On the other hand, some disadvantages include:  The initial investment is more as compared with conventional refrigeration.  The magneto caloric materials are rare earth materials hence their availability also adds up an disadvantage in MAGNETIC REFRIGERATION.  GMCE materials need to be developed to allow higher frequencies of rectilinear and rotary magnetic refrigerators  Protection of electronic components from magnetic fields. But notice that they are static, of short range and may be shielded  Permanent magnets have limited field strength. Electromagnets and superconducting magnets are (too) expensive  Temperature changes are limited. Multi-stage machines lose effi ciency through the heat transfer between the stages  Moving machines need high precision to avoid magnetic field reduction due to gaps between the magnets and the magneto caloric material.



18

18. 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 MCE 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.



19 19. 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 pre cooled by the AMRR only. In this case it is assumed that the magnetic refrigeration system pre cools the hydrogen from 300 K to 22 K using approximately 7-9 stages of AMRR. In the second case, the supplied hydrogen is pre cooled 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 pre cooled 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 pre cooling. 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



20

20. CONCLUSION If we say future perspectives of room temperature Magnetic Refrigeration; It can be seen from the earlier Description that main progresses have been made in America. However, with the continual phasic progresses of Room temperature magnetic refrigeration, the whole world Has accelerated in the research. Nevertheless, it is notable that main work is concentrated On investigations of magnetic materials, lack of Experimental explorations of magnetic refrigerator. From The former results achieved by researchers, it can be seen That there is still a great performance difference between Magnetic refrigerator and vapor compression refrigerator in Terms of cooling capacity and temperature span. The number of reserach papers puplished.The number of near room temparature magnetic Refrigerators reported. At the end of this study we can say;  It 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.  Magnetic materials available for room Temperature magnetic refrigeration are mainly Gd, Gdsige alloys, mnas-like materials, perovskitelike Materials,  Materials under development for room Temparature magnetic refrigeration are La(fexsi1X)13 and La(Fe0.88Si0.12)13Hy  Excellent behavior of regeneration and heat Transfer is required  It can be use household refrigerator, central Cooling systems, room air conditioners and Supermarket refrigeration applications.  This technology must be universalized worldwide.



21 21. REFERENCES

1. http://en.wikipedia.org/wiki/Magnetic_refrigeration

2. http://www.scribd.com/doc/19537314/Magnetic-Refrigeration

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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