Magnetic refrigeration Seminar Report

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Magnetic refrigeration Seminar Report

  1. 1. 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 2009-13Guided By: - Submitted By: -Mr. Narayan Lal Jain Aman AgrawalReader, 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
  2. 2. DEPARTMANT OF MECHNICAL ENGINEERING VIVEKANANDA INSTITUTE OF TECHNOLOGY - EAST JAIPUR-303012 CERTIFICATE This is to certify that the seminar entitled “Magnetic Refrigeration”, has beencarried out by Aman agrawal under my guidance in partial fulfillment of the degree ofbachelor of engineering in Mechanical Engineering of Rajasthan Technical University,Kota, during the academic session 2009 - 2013. To the best of my knowledge and beliefthis work has not been submitted elsewhere for the best award of any other degree. Thework has been found satisfactory and is approved for submission.GUIDE:(Sign by Guide) (Sign by HOD)Mr. Narayan Lal Jain Mr. Rahul GoyalReader, H.O.DDeptt. of M.E. Deptt. of M.E.VIT - East, Jaipur VIT - East, Jaipur
  3. 3. 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) Magnetic Refrigeration 1
  4. 4. ABSTRACTThe objective of this effort is to study the Magnetic Refrigeration which uses solid materials asthe refrigerant. These materials demonstrate the unique property known as magneto caloriceffect, which means that they increase and decrease in temperature whenmagnetized/demagnetized. This effect has been observed for many years and was used forcooling near absolute zero. Recently materials are being developed which have sufficienttemperature and entropy change to make them useful for a wide range temperature applications. Magnetic refrigeration is an emerging technology that exploits the magnetocaloric effectfound in solid state refrigerants. The combination of solid-state refrigerants, water based heattransfer fluids and high efficiency leads to environmentally desirable products with minimalcontribution to global warming. Among the numerous application of refrigeration technology airconditioning applications provide the largest aggregate cooling power and use of the greatestquantity of electric energy.Deptt. Of Mechanical Engineering (Vit-east, Jaipur) Magnetic Refrigeration 2
  5. 5. TABLE1.INTRODUCTION ...................................................................................................................72. HISTORY ...............................................................................................................................83.REFRIGERATION .................................................................................................................9 3.1 Unit of Refrigeration:- ................................................................................................................. 94. 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 : - ....................................................................................................................... 175. OZONE LAYER DEPLETION ............................................................................................186. OBJECTIVES OF MAGNETIC REFRIGERATION ..........................................................197. MAGNETO CALORIC EFFECT ........................................................................................208. WORKING PRINCIPLE ......................................................................................................219.WORKING OF MAGNETIC REFRIGERATION SYSTEM ................................................22 9.1 Magnetic Refrigeration system : - ............................................................................................. 22 9.2 Refrigerator Configuration :- ................................................................................................... 2310. 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 :- ........................................................................................... 2711. COMPARISON BETWEEN MAGNETIC REFRIGERATION AND CONVENTIONALREFRIGERATION ..................................................................................................................2812. COMPONENTS .................................................................................................................30Deptt. Of Mechanical Engineering (Vit-east, Jaipur) Magnetic Refrigeration 3
  6. 6. 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 (AMRs) :- .............................................................................. 3614. APPLICATIONS ................................................................................................................38 14.1 A rotary AMR liquefier :- ........................................................................................................ 38 14.2 Future Applications:- ............................................................................................................... 3915. BENEFITS .........................................................................................................................40 15.1 TECHNICAL :- ...................................................................................................................... 40 15.2 SOCIO-ECONOMIC :- ........................................................................................................... 4016. ADVANTAGES .....................................................................................................................41 16.1 Advantages over Vapour compression and Vapour absorption Cycles :- ............................. 41 16.2 Potential Advantages : - ........................................................................................................... 4217. DISADVANTAGES ............................................................................................................4318. CURRENT AND FUTURE USES .....................................................................................4419. CASE STUDY.....................................................................................................................4520. CONCLUSION ...................................................................................................................4621. REFERENCES ..................................................................................................................47Deptt. Of Mechanical Engineering (Vit-east, Jaipur) Magnetic Refrigeration 4
  7. 7. 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 Deptt. Of Mechanical Engineering (Vit-east, Jaipur) Magnetic Refrigeration 5
  8. 8. CONTENTS ACKNOWLEDGEMENT…………………………………….……………….…...I ABSTRACT………………………………………………………………………...II INDEX…………………………………………………………………....................III FIGURE INDEX…………………………………………………………………….IV1.INTRODUCTION ............................................................................................................................... 72. HISTORY ........................................................................................................................................... 83.REFRIGERATION ............................................................................................................................. 94. METHODS OF REFRIGERATION ................................................................................................ 105. OZONE LAYER DEPLETION......................................................................................................... 186. OBJECTIVES OF MAGNETIC REFRIGERATION ...................................................................... 197. MAGNETO CALORIC EFFECT ..................................................................................................... 208. WORKING PRINCIPLE .................................................................................................................. 219.WORKING OF MAGNETIC REFRIGERATION SYSTEM............................................................. 2210. MAGNETIC REFRIGERATION CYCLE ...................................................................................... 2511. COMPARISON BETWEEN MAGNETIC REFRIGERATION AND CONVENTIONALREFRIGERATION .............................................................................................................................. 2812. COMPONENTS.............................................................................................................................. 3013. REQUIREMENTS FOR PRATICAL APPLICATIONS ................................................................ 3214. APPLICATIONS ............................................................................................................................ 3815. BENEFITS ..................................................................................................................................... 4016. ADVANTAGES .................................................................................................................................. 4117. DISADVANTAGES ........................................................................................................................ 4318. CURRENT AND FUTURE USES .................................................................................................. 4419. CASE STUDY ................................................................................................................................. 4520. CONCLUSION ............................................................................................................................... 4621. REFERENCES............................................................................................................................... 47Deptt. Of Mechanical Engineering (Vit-east, Jaipur) Magnetic Refrigeration 6
  9. 9. 1 1. INTRODUCTIONRefrigeration is the process of removing heat from matter which may be a solid, a liquid, or agas. Removing heatfrom the matter cools it, or lowers its temperature. In the mechanicalrefrigeration a refrigerant is a substance capable of transferring heat that it absorbs at lowtemperatures and pressures to a condensing medium; inthe region of transfer, the refrigerant is athigher 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 coolingmedium. Our society is highly dependent on reliable cooling technology. Refrigeration iscritical toour health and the global economy. Consumer application includes airconditioning, foodpreservation, air dehumidification, beverage dispensing and ice making without refrigeration thefood supply wood still be seasonal and limited to locally produced non-perishable items. Modern refrigeration is almost entirely based on a compression/ expansionrefrigerationcycle. It is a mature, reliable & relatively low cost technology. Over the years,all parts of aconventional refrigerator were considerably improved due to extendedresearch and developmentefforts. Furthermore, some liquids used as refrigerants arehazardous chemicals, while othereventually escape into the environment contributingtowards ozone layer depletion and globalwarming and therefore, conventionalrefrigeration ultimately promotes deleterious trends in theglobal climate. Magnetic refrigerator, which has advantages in refrigeration efficiency, reliability, lownoise and environmental friendliness with respect to the conventional gas refrigerators, isbecoming a promising technology to replace the conventional technique. The development of themagnetic material, magnetic refrigeration cycles, magnetic field and therefrigerator of roomtemperature magnetic refrigeration is introduced.Deptt. Of Mechanical Engineering (Vit-east, Jaipur) Magnetic Refrigeration 7
  10. 10. 2 2. HISTORYThe effect was discovered in pure iron in 1881 by E. Warburg. Originally, the cooling effectvaried between 0.5 to 2 K/T. Major advances first appeared in the late 1920s when cooling via adiabaticdemagnetization was independently proposed by two scientists: Debye (1926) and Giauque(1927). The process was demonstrated a few years later when Giauque and MacDougall in 1933used it to reach a temperature of 0.25 K. Between 1933 and 1997, a number of advances inutilization of the MCE for cooling occurred. This cooling technology was first demonstrated experimentally by chemist NobelLaureate William F. Giauque and his colleague Dr. D.P. MacDougall in 1933 for cryogenicpurposes (they reached 0.25 K) In 1997, the first near room temperature proof of concept magnetic refrigerator wasdemonstrated by Prof. Karl A. Gschneidner, Jr. by the Iowa State University at AmesLaboratory. This event attracted interest from scientists and companies worldwide that starteddeveloping new kinds of room temperature materials and magnetic refrigerator designs.Refrigerators based on the magneto caloric effect have been demonstrated in laboratories, usingmagnetic fields starting at 0.6 T up to 10 teslas. Magnetic fields above 2 T are difficult toproduce with permanent magnets and are produced by a superconducting magnet (1 tesla is about20,000 times the Earths magnetic field).Deptt. Of Mechanical Engineering (Vit-east, Jaipur) Magnetic Refrigeration 8
  11. 11. 3 3.REFRIGERATIONRefrigeration is the process of removing heat from an enclosed space, or from a substance, andmoving it to a place where it is unobjectionable. The primary purpose of refrigeration is loweringthe 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. Coldis 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 mustbe performed to accomplish this. This work is traditionally done by mechanical work but canalso 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. Commercialrefrigerators in the US are mostly rated in tons of refrigeration, but elsewhere in kW. One ton ofrefrigeration capacity can freeze one short ton of water at 0 °C (32 °F) in 24 hours. Based onthat:Latent heat of ice (i.e., heat of fusion) = 333.55 kJ/kg ≈ 144 Btu/lb. One short ton = 2000 lb Heatextracted = (2000) (144)/24 hr. = 288000 Btu/24 hr. = 12000 Btu/hr. =200 Btu/min1 tonrefrigeration = 200 Btu/min = 3.517 kJ/s = 3.517kWA 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 1to 5 tons of refrigeration.Deptt. Of Mechanical Engineering (Vit-east, Jaipur) Magnetic Refrigeration 9
  12. 12. 4 4. METHODS OF REFRIGERATIONMethods 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 dryice (frozen carbon dioxide). These methods are used for small-scale refrigeration such as inlaboratories and workshops, or in portable coolers. Ice owes its effectiveness as a cooling agent to its melting point of 0 °C (32 °F) at sealevel. To melt, ice must absorb 333.55 kJ/kg (about 144 Btu/lb) of heat. Foodstuffs maintainednear this temperature have an increased storage life. Solid carbon dioxide has no liquid phase at normal atmospheric pressure, and sublimesdirectly from the solid to vapor phase at a temperature of -78.5 °C (-109.3 °F), and is effectivefor maintaining products at low temperatures during sublimation. Systems such as this where therefrigerant 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 orsource 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-temperaturesource to the engine, part of the heat being used to produce work and the rest being rejected to alow-temperature sink. This satisfies the second law of thermodynamics. A refrigeration cycle describes the changes that take place in the refrigerant as italternately absorbs and rejects heat as it circulates through a refrigerator. It is also appliedDeptt. Of Mechanical Engineering (Vit-east, Jaipur) Magnetic Refrigeration 10
  13. 13. 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 storagevolume by pumping heat from a lower temperature heat source into a higher temperature heatsink. Insulation is used to reduce the work and energy needed to achieve and maintain a lowertemperature in the cooled space. The operating principle of the refrigeration cycle was describedmathematically beside in 1824 as a heat engine.The most common types of refrigeration systems use the reverse-Rankine vapor-compressionrefrigeration cycle, although absorption heat pumps are used in a minority of applications.Cyclic refrigeration can be classified as: 1. Vapour cycle, and 2. Gas cycle4.2.1 Vapour Cycle Refrigeration:-Vapour cycle refrigeration can further be classified as: 1. Vapor-compression refrigeration 2. Vapor-absorption refrigeration4.2.1.1 Vapor-compression refrigeration :The vapour-compression cycle is used in most household refrigerators as well as in many largecommercial and industrial refrigeration systems. Figure 1 provides a schematic diagram of thecomponents of a typical vapor-compression refrigeration system. The thermodynamics of the cycle can be analyzed on a diagram as shown in Figure 2. Inthis cycle, a circulating refrigerant such as Freon enters the compressor as a vapor. From point 1to point 2, the vapor is compressed at constant entropy and exits the compressor as a vapor at aDeptt. Of Mechanical Engineering (Vit-east, Jaipur) Magnetic Refrigeration 11
  14. 14. higher temperature, but still below the vapor pressure at that temperature. From point 2 to point 3and on to point 4, the vapor travels through the condenser which cools the vapor until it startscondensing, and then condenses the vapor into a liquid by removing additional heat at constantpressure and temperature. Between points 4 and 5, the liquid refrigerant goes throughthe expansion valve (also called a throttle valve) where its pressure abruptly decreases, causingflash and auto-refrigeration of, typically, less than half of the liquid. Figure 1: Vapor compression refrigeration Figure 2: Temperature–Entropy diagramDeptt. Of Mechanical Engineering (Vit-east, Jaipur) Magnetic Refrigeration 12
  15. 15. That results in a mixture of liquid and vapor at a lower temperature and pressure as shown atpoint 5. The cold liquid-vapor mixture then travels through the evaporator coil or tubes and iscompletely vaporized by cooling the warm air (from the space being refrigerated) being blownby a fan across the evaporator coil or tubes. The resulting refrigerant vapor returns to thecompressor inlet at point 1 to complete the thermodynamic cycle. The above discussion is based on the ideal vapor-compression refrigeration cycle, anddoes not take into account real-world effects like frictional pressure drop in the system, slightthermodynamic irreversibility during the compression of the refrigerant vapor, or non-idealgas behavior (if any).4.2.1.2 Vapor absorption cycle:-In the early years of the twentieth century, the vapor absorption cycle using water-ammoniasystems was popular and widely used. After the development of the vapor compression cycle, thevapor absorption cycle lost much of its importance because of its low coefficient ofperformance (about one fifth of that of the vapor compression cycle). Today, the vaporabsorption cycle is used mainly where fuel for heating is available but electricity is not, such asin recreational vehicles that carry LP gas. It is also used in industrial environments whereplentiful waste heat overcomes its inefficiency. Figure 3: Vapor absorption cycleDeptt. Of Mechanical Engineering (Vit-east, Jaipur) Magnetic Refrigeration 13
  16. 16. The absorption cycle is similar to the compression cycle, except for the method of raisingthe pressure of the refrigerant vapor. In the absorption system, the compressor is replaced by anabsorber which dissolves the refrigerant in a suitable liquid, a liquid pump which raises thepressure and a generator which, on heat addition, drives off the refrigerant vapor from the high-pressure 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 anabsorption refrigerator, a suitable combination of refrigerant and absorbent is used. The mostcommon 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 doesnt change phase, therefrigeration cycle is called a gas cycle. Air is most often this working fluid. As there is nocondensation and evaporation intended in a gas cycle, components corresponding to thecondenser and evaporator in a vapor compression cycle are the hot and cold gas-to-gas heatexchangers in gas cycles. The gas cycle is less efficient than the vapor compression cycle because the gas cycleworks on the reverse Brayton cycle instead of the reverse Rankine cycle. As such the workingfluid does not receive and reject heat at constant temperature. In the gas cycle, the refrigerationeffect is equal to the product of the specific heat of the gas and the rise in temperature of the gasin the low temperature side. Therefore, for the same cooling load, a gas refrigeration cycle needsa large mass flow rate and is bulky. Because of their lower efficiency and larger bulk, air cycle coolers are not often usednowadays in terrestrial cooling devices. However, the air cycle machine is very common on gasturbine-powered jet aircraft as cooling and ventilation units, because compressed air is readilyavailable from the engines compressor sections. Such units also serve the purpose ofpressurizing the aircraft.Deptt. Of Mechanical Engineering (Vit-east, Jaipur) Magnetic Refrigeration 14
  17. 17. Figure 4: Gas cycle A schematic diagram of an air refrigeration system working on a simple gas cycle isshown below. In this arrangement, the compressor and the expander are shown coupled togethersince the expander work is utilized to provide a part of the compressor work. Point 4 in the figurerepresents the state of the refrigerated air, which would absorb heat at a constant pressure until itattains 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 thesurrounding atmospheric air as the cycle is presently employed only in aircraft refrigeration. Theair is finally expanded isentropically to 4 whereby it gets cooled. In this system other gases likeHydrogen, 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 twodifferent types of materials. A Peltier cooler, heater, or thermoelectric heat pump is a solid-stateactive heat pump which transfers heat from one side of the device to the other, with consumptionof electrical energy, depending on the direction of the current. Such an instrument is also called aPeltier device, Peltier heat pump, solid state refrigerator, or thermoelectric cooler (TEC). TheyDeptt. Of Mechanical Engineering (Vit-east, Jaipur) Magnetic Refrigeration 15
  18. 18. can be used either for heating or for cooling (refrigeration), although in practice the mainapplication 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-compressionrefrigeration is. The main advantages of a Peltier cooler (compared to a vapor-compressionrefrigerator) are its lack of moving parts or circulating liquid, and its small size and flexibleshape (form factor). Its main disadvantage is high cost and poor power efficiency. Manyresearchers 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 acooler, a voltage is applied across the device, and as a result, a difference in temperature willbuild up between the two sides.[2] When operated as a generator, one side of the device is heatedto a temperature greater than the other side, and as a result, a difference in voltage will build upbetween the two sides (the Seebeck effect). However, a well-designed Peltier cooler will be amediocre thermoelectric generator and vice-versa, due to different design and packagingrequirements.Deptt. Of Mechanical Engineering (Vit-east, Jaipur) Magnetic Refrigeration 16
  19. 19. 4.4 Magnetic refrigeration :-Magnetic refrigeration, or adiabatic demagnetization, is a cooling technology based on themagneto caloric effect, an intrinsic property of magnetic solids. The refrigerant is oftena paramagnetic salt, such as cerium magnesium nitrate. The active magnetic dipoles in this caseare those of the electron shells of the paramagnetic atoms. A strong magnetic field is applied to the refrigerant, forcing its various magnetic dipolesto align and putting these degrees of freedom of the refrigerant into a state of lowered entropy. Aheat sink then absorbs the heat released by the refrigerant due to its loss of entropy. Thermalcontact with the heat sink is then broken so that the system is insulated, and the magnetic field isswitched off. This increases the heat capacity of the refrigerant, thus decreasing its temperaturebelow the temperature of the heat sink. Because few materials exhibit the needed properties at room temperature, applicationshave 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 vortextube used for spot cooling, when compressed air is available; and thermoacousticrefrigeration using sound waves in a pressurized gas to drive heat transfer and heatexchange; 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 heatengines can be run backwards to act as a refrigerator, and therefore these engines have a nicheuse in cryogenics. In addition there are other types of cryocoolers such as Gifford-McMahoncoolers, Joule-Thomson coolers, pulse-tube refrigerators and, for temperatures between 2 mKand 500 mK, dilution refrigerators.Deptt. Of Mechanical Engineering (Vit-east, Jaipur) Magnetic Refrigeration 17
  20. 20. 5 5. OZONE LAYER DEPLETIONOzone depletion describes two distinct but related phenomena observed since the late 1970s: asteady decline of about 4% per decade in the total volume of ozone in Earthsstratosphere (the ozone layer), and a much larger springtime decrease in stratospheric ozone overEarths polar regions. The latter phenomenon is referred to as the ozone hole. In addition to thesewell-known stratospheric phenomena, there are also springtime polartropospheric ozonedepletion events. The main source of these halogen atoms in the stratosphere is photo dissociation of man-made halocarbon refrigerants (CFCs, freons, halons). These compounds are transported into thestratosphere after being emitted at the surface.[2] Both types of ozone depletion were observed toincrease 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) ofultraviolet light (UV light) from passing through the Earths atmosphere, observed and projecteddecreases in ozone have generated worldwide concern leading to adoption of the MontrealProtocol that bans the production of CFCs, halons, and other ozone-depleting chemicals suchas carbon tetrachloride and trichloroethane. It is suspected that a variety of biologicalconsequences such as increases in skin cancer, cataracts,[3] damage to plants, and reduction ofplankton populations in the oceans photic zone may result from the increased UV exposure dueto ozone depletion. An international agreement – Montreal Protocol was signed by all countries in order toprevent further depletion of the Ozone layer. According to this international agreement, the useof fully halogenated CFC’s, like R11, R12, R13, R14 and R5O2, was phased out by 2000 AD.Deptt. Of Mechanical Engineering (Vit-east, Jaipur) Magnetic Refrigeration 18
  21. 21. 6 6. OBJECTIVES OF MAGNETIC REFRIGERATION To develop more efficient and cost effective small scale H2 liquefiers as an alternative tovapor-compression cycles using magnetic refrigeration. With the help of magnetic refrigeration our objective is to solve the problem of hydrogenstorage as it ignites on a very low temperature. Hydrogen Research Institute (HRI) is studying itwith the help of magnetic refrigeration. We provide the cooling for the hydrogen storage byliquefying it. The hydrogen can be liquefied at a low temperature and the low temperature is achievedwith the help of magnetic refrigeration. Thus, the magnetic refrigeration also provides a method to store hydrogen by liquefyingit. The term used for such a device is magnetic liquefier.Deptt. Of Mechanical Engineering (Vit-east, Jaipur) Magnetic Refrigeration 19
  22. 22. 7 7. MAGNETO CALORIC EFFECTThe Magneto caloric effect (MCE, from magnet and calorie) is a magneto-thermodynamicphenomenon in which a reversible change in temperature of a suitable material is caused byexposing the material to a changing magnetic field. This is also known as adiabaticdemagnetization by low temperature physicists, due to the application of the processspecifically to affect a temperature drop. In that part of the overall refrigeration process, adecrease in the strength of an externally applied magnetic field allows the magnetic domains of aChosen (magneto caloric) material to become disoriented from the magnetic field by theagitatingAction of the thermal energy (phonons) present in the material. If the material is isolated so thatno 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 Curietemperature, except that magnetic dipoles overcome a decreasing external magnetic field whileenergy remains constant, instead of magnetic domains being disrupted from internalferromagnetism as energy is added. One of the most notable examples of the magneto caloric effect is in the chemicalelement gadolinium and some of its alloys. Gadoliniums temperature is observed to increasewhen it enters certain magnetic fields. When it leaves the magnetic field, the temperature returnsto 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 hasallowed scientists to approach within one thousandth of a degree of absolute zero.Magnetic Refrigeration is also called as Adiabatic Magnetization.Deptt. Of Mechanical Engineering (Vit-east, Jaipur) Magnetic Refrigeration 20
  23. 23. 8 8. WORKING PRINCIPLEAs shown in the figure, when the magnetic material is placed in the magnetic field, thethermometer 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, thethermometer 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 placeand as its temperature increases, it will absorb heat from that place and by taking the magneticmaterial outside in the surroundings, we will remove the magnetic material from magnetic fieldand thus it will lose heat as its temperature decreases and hence the cycle repeats over and againto provide the cooling effect at the desired place.Deptt. Of Mechanical Engineering (Vit-east, Jaipur) Magnetic Refrigeration 21
  24. 24. 9 9.WORKING OF MAGNETIC REFRIGERATION SYSTEM9.1 Magnetic Refrigeration system : - Consists of two beds containing spherical powder of Gadolinium with water being usedas the heat transfer fluid. The magnetic field for this system is 5 Wb/m2, providing a temperaturespan of 38 K. The process flow diagram for the magnetic refrigeration system is shown inFigure-6.3. Figure 7: Flow process diagram (a) A mixture of water and ethanol serves as the heat transfer fluid for the system. The fluidfirst passes through the hot heat exchanger, which uses air to transfer heat to the atmosphere. TheDeptt. Of Mechanical Engineering (Vit-east, Jaipur) Magnetic Refrigeration 22
  25. 25. fluid then passes through the copper plates attached to the no magnetized cooler-magneto caloricbeds and loses heat. A fan blows air over this cold fluid into the freezer to keep the freezertemperature at approximately 0°F. The heat transfer fluid then gets heated up to 80°F, as itpasses 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 simultaneouslymove up and down, into and out of the magnetic field. The second position of the beds is shownin Figure 6.4. The cold air from the freezer is blown into the refrigerator by the freezer fanshown 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 thefreezer represents approximately 30% of this volume. Freezers are designed to maintain atemperature of 0°F. Refrigerators maintain a temperature of 39°F. The refrigerator will beinsulated with polyurethane foam, one of the most common forms of insulation available. Therefrigerator is kept cool by forcing cold air from the freezer into the refrigerator by using a smallfan. Figure 8: Flow process diagram(b) The control system for maintaining the desired internal temperatures consists of twothermostats with on/off switches. The freezer thermostat regulates the temperature by turning theDeptt. Of Mechanical Engineering (Vit-east, Jaipur) Magnetic Refrigeration 23
  26. 26. compressor off when the temperature gets below 0°F. A second thermostat regulates the fan thatcools the refrigerator to 39°F. To maintain a frost-free environment in the freezer, a defrost timerwill 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 apan at the base of the refrigerator. The next nine minutes involve the safety factor of not reachinga temperature in the freezer that is too high. Also, a safety thermostat keeps the liquid water fromfreezing as it drains. The heat transfer fluid for the magnetic refrigeration system is a liquid alcohol watermixture. The mixture used in the design consists of 60 % ethanol and 40 % water. This mixturehas a freezing point of –40°F, assuring that the mixture does not freeze at operatingtemperatures. This heat transfer fluid is cheaper than traditional refrigerants and also eliminatesthe 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 heattransfer fluid, at approximately 70°F, gets cooled to –12°F by the non-magnetized cold set ofbeds. This cooled fluid is then sent to the cold heat exchanger, where it absorbs the 15 excessheats from the freezer. This fluid leaves the freezer at 0°F. The warm fluid then flows throughthe opposite magnetized set of beds, where it is heated up to 80°F. This hot stream is now cooledby air at room temperature in the hot heat exchanger to 70°F. The cycle then repeats itself everythree seconds after the beds have switched positions. Copper tubing is used throughout the loopand in the two heat exchangers. The two sets of beds contain the small spheres of magnetocaloric material. The beds are alternated in and out of the magnetic field using a chain andsprocket drive shaft. The drive shaft rotates the beds back and forth while still keeping them incontact with the heat transfer plates.Deptt. Of Mechanical Engineering (Vit-east, Jaipur) Magnetic Refrigeration 24
  27. 27. 10 10. MAGNETIC REFRIGERATION CYCLEThe magnetic refrigeration is mainly based on magneto caloric effect according to which Somematerials change in temperature when they are magnetized and demagnetized. Near the phase transition of the magnetic materials, the adiabatic application of amagnetic field reduces the magnetic entropy by ordering the magnetic moments. This results in atemperature increase of the magnetic material. This phenomenon is practically reversible forsome magnetic materials; thus, adiabatic removal of the field revert the magnetic entropy to itsoriginal state and cools the material accordingly. This reversibility combined with the ability tocreate devices with inherent work recovery, makes magnetic refrigeration a potentially moreefficient process than gas compression and expansion. The efficiency of magnetic refrigerationcan be as much as 50% greater than for conventional refrigerators. The process is performed as a refrigeration cycle, analogous to the Carnot cycle, and canbe described as a starting point whereby the chosen working substance is introduced into amagnetic field (i.e. the magnetic flux density is increased). The working material is therefrigerant, and starts in thermal equilibrium with the refrigerated environment. Figure 9: Magneto caloric EffectDeptt. Of Mechanical Engineering (Vit-east, Jaipur) Magnetic Refrigeration 25
  28. 28. Figure 10: Magnetic Refrigeration cycle v/s Vapor Cycle RefrigerationProcess is similar to gas compression and expansion cycle as used in regular refrigerationcycle.Steps of thermodynamic Cycle:- 1. Adiabatic Magnetization 2. Isomagnetic Enthalpy Transfer 3. Adiabatic demagnetization 4. Isomagnetic Entropic Transfer10.1 Adiabatic Magnetization :-In first step of cycle,  A magneto caloric Substance placed in an insulated environment.Deptt. Of Mechanical Engineering (Vit-east, Jaipur) Magnetic Refrigeration 26
  29. 29.  Externally applied Magnetic field (+H) increased.  This causes the magnetic dipoles of the atoms to align, thereby decreasing the materials 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) Magnetic Refrigeration 27
  30. 30. 11 11. COMPARISON BETWEEN MAGNETIC REFRIGERATION AND CONVENTIONAL REFRIGERATION Figure 11: Comparison between Magnetic Refrigeration and Conventional RefrigerationIn Figure 2 the four basic steps of a conventional gascompression/ Expansion refrigerationprocess 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 fora cooling process in two steps. The main Cooling usually occurs through the expansion of thegas. The steps of a magnetic refrigeration process are Analogous. By comparing a with b, inFigure.2 one can see That instead of compression of a gas, a magnetocaloric Material is movedDeptt. Of Mechanical Engineering (Vit-east, Jaipur) Magnetic Refrigeration 28
  31. 31. into a magnetic field and that instead of Expansion it is moved out of the field. As explained inthe Previous section, these processes change the temperature Of the material and heat may beextracted, respectively Injected just as in the conventional process. There are Some differencesbetween the two processes. The heat Injection and rejection in a gaseous refrigerant is a ratherFast process, because turbulent motion transports heat Very fast. Unfortunately, this is not thecase in the solid Magnetocaloric materials. Here, the transport mechanism For heat is slowmolecular diffusion. Therefore, at present fi Ligree porous structures are considered to be thebest Solution to overcome this problem. The small distances From the central regions of thematerial to an adjacent fluid Domain, where a heat transport fluid captures the heat andTransports it out of the material, are ideal to make the Magnetic cooling process faster.Furthermore, the not very Large adiabatic temperature differences of magnetocaloric Materialswill require more often a design of cascade or Regenerative magnetic refrigerators than inconventional Refrigerators and hence require additional heat transfer Steps. In the Figure.2 (a) isthe conventional gascompression Process is driven by continuously repeating The four differentbasic processes shown and (b) is the Magnetic refrigeration cycle comparison. Compression isReplaced by adiabatic magnetization and expansion by Adiabatic demagnetization. (A) (b) Figure 12 : Refrigeration cycles for conventional gas compression and magnetic refrigerationDeptt. Of Mechanical Engineering (Vit-east, Jaipur) Magnetic Refrigeration 29
  32. 32. 12 12. COMPONENTSComponents required for construction :- 1. Magnets 2. Hot Heat exchanger 3. Cold Heat Exchanger 4. Drive 5. Magneto caloric wheel Figure 13: ComponentsDeptt. Of Mechanical Engineering (Vit-east, Jaipur) Magnetic Refrigeration 30
  33. 33. 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.Deptt. Of Mechanical Engineering (Vit-east, Jaipur) Magnetic Refrigeration 31
  34. 34. 13 13. REQUIREMENTS FOR PRATICAL APPLICATIONSThere 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 beused in practical refrigeration systems. The search for the "best" materials is focused on rareearthmetals, 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 thermalresponse of a solid to the application or removal of magnetic fields is maximized when the solidis near its magnetic ordering temperature. The magnitudes of the magnetic entropy and the adiabatic temperature changes arestrongly dependent upon the magnetic order process: the magnitude is generally small inantiferromagnets, ferrimagnets and spin glass systems; it can be substantial for normalferromagnets which undergo a second order magnetic transition; and it is generally the largest fora ferromagnet which undergoes a first order magnetic transition. Also, crystalline electric fields and pressure can have a substantial influence on magneticentropy and adiabatic temperature changes. Currently, alloys of gadolinium producing 3 to 4 Kper tesla of change in a magnetic field can be used for magnetic refrigeration or powergeneration 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 mostpromising substitutes for Gadolinium and its alloys (GdDy, GdTy, etc...). These materials arecalled giant magnetocaloric effect materials (GMCE). Gadolinium and its alloys are the bestDeptt. Of Mechanical Engineering (Vit-east, Jaipur) Magnetic Refrigeration 32
  35. 35. material available today for magnetic refrigeration near room temperature since they undergosecond-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 roomtemperature magnetic refrigerator in 1976, the research range for magnetic refrigeration workingmaterials has been greatly expanded. At first, some ferromagnets concerning the second ordertransition were investigated for the large MCE existing inthem. Recently the magnetic materialsundergoing a firstorder magnetic transition become the focus after the giant MCE was found inGdSiGe alloys.Deptt. Of Mechanical Engineering (Vit-east, Jaipur) Magnetic Refrigeration 33
  36. 36. Some magnetic materials that are promise to be used in the future, the following list ofpromising 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 problemwith using pure gadolinium as the refrigerant material is that it does not exhibit a strong magnetocaloric effect at room temperature. More recently, however, it has been discovered that arc-melted alloys of gadolinium, silicon, and germanium are more efficient at room temperature.The prototype magnetic material available for room temperature magnetic refrigeration is thelanthanide metal gadolinium (Gd). At the Curie temperature of 294 K, Gd undergoes a second-order paramagnetic – ferromagnetic phase transition. The MCE and the heat capacity of Gdhave been studied in many research activities. However, many urgent problems such aseasy oxidation, hard preparation, and high price, need to be settled before they are applied inroom 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 theseporous solids are used in refrigerators, they are referred to as "regenerators”. Typical regenerator geometries include: (a) TubesDeptt. Of Mechanical Engineering (Vit-east, Jaipur) Magnetic Refrigeration 34
  37. 37. (b) Perforated plates (c) Wire screens (d) Particle beds Figure 15: Regenerators13.3 Super Conducting Magnets :- Most practical magnetic refrigerators are based on superconducting magnets operating atcryogenic temperatures (i.e., at -269 C or 4 K).These devices are electromagnets that conductelectricity with essentially no resistive losses. The superconducting wire most commonly used ismade of a Niobium-Titanium alloy. Only superconducting magnets can provide sufficientlyDeptt. Of Mechanical Engineering (Vit-east, Jaipur) Magnetic Refrigeration 35
  38. 38. strong magnetic fields for most refrigeration applications. A typical field strength is 8 Tesla(approximately 150,000 times the Earths magnetic field).An 8 Tesla field can produce amagneto caloric temperature change of up to 15 C in some rare-earth materials. Figure 16: Super Conducting Magnets13.4 Active Magnetic Regenerators (AMRs) :-Deptt. Of Mechanical Engineering (Vit-east, Jaipur) Magnetic Refrigeration 36
  39. 39. A regenerator that undergoes cyclic heat transfer operations and the magneto caloriceffect is called an Active Magnetic Regenerator (AMR).An AMR should be designed to possessthe following attributes: These requirements are often contradictory, making AMRs difficult to design andfabricate. 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 manufactureDeptt. Of Mechanical Engineering (Vit-east, Jaipur) Magnetic Refrigeration 37
  40. 40. 14 14. APPLICATIONS14.1 A rotary AMR liquefier :-The Cryofuel Systems Group is developing an AMR refrigerator for the purpose of liquefyingnatural gas. A rotary configuration is used to move magnetic material into and out of asuperconducting magnet. This technology can also be extended to the liquefaction of hydrogen. Figure 17: A rotary AMR liquefierDeptt. Of Mechanical Engineering (Vit-east, Jaipur) Magnetic Refrigeration 38
  41. 41. 14.2 Future Applications:-In general, at the present stage of the development of magnetic refrigerators with permanentmagnets, hardly any freezing applications are feasible. These results, because large temperaturespans occur between the heat source and the heat sink. An option to realize magnetic freezingapplications could be the use of superconducting magnets. However, this may only be economicin the case of rather large refrigeration units. Such are used for freezing, e.g. in cooling plants inthe 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 electronicsDeptt. Of Mechanical Engineering (Vit-east, Jaipur) Magnetic Refrigeration 39
  42. 42. 15 15. BENEFITS15.1 TECHNICAL :-High efficiency: - As the magneto caloric effect is highly reversible, the thermo dynamicefficiency of the magnetic refrigerator is high. It is somewhat 50% more than VaporCompression 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 thereason that in case of magnetic refrigeration the working substance is a solid material (saygadolinium) 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 theatmosphere and hence is reliable one.15.2 SOCIO-ECONOMIC :-Competition in global market:- Research in this field will provide the opportunity so that newindustries 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 notthere 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 theywill be the key factor for new emerging technologies in this worldDeptt. Of Mechanical Engineering (Vit-east, Jaipur) Magnetic Refrigeration 40
  43. 43. 16 16. ADVANTAGES16.1 Advantages over Vapour compression and Vapour absorption Cycles :-Magnetic refrigeration performs essentially the same task as traditional compression-cycle gasrefrigeration technology. Heat and cold are not different qualities; cold is merely the relativeabsence of heat. In both technologies, cooling is the subtraction of heat from one place (theinterior of a home refrigerator is one common place example) and the dumping of that heatanother place (a home refrigerator releases its heat into the surrounding air). As more and moreheat is subtracted from this target, cooling occurs. Traditional refrigeration systems - whetherair-conditioning, freezers or other forms - use gases that are alternately expanded andcompressed to perform the transfer of heat. Magnetic refrigeration systems do the same job, butwith metallic compounds, not gases. Compounds of the element gadolinium are most commonlyused in magnetic refrigeration, although other compounds can also be used. Magnetic refrigeration is seen as an environmentally friendly alternative to conventionalvapor- cycle refrigeration. And as it eliminates the need for the most inefficient part of todaysrefrigerators, the compressor, it should save costs. New materials described in this issue maybring practical magneto caloric cooling a step closer. A large magnetic entropy change has beenfound to occur in MnFeP0.45As0.55 at room temperature, making it an attractive candidate forcommercial applications in magnetic refrigeration. The added advantages of MR over GasCompression Refrigerator are compactness, and higher reliability due to Solid working materialsinstead of a gas, and fewer and much slower moving parts our work in this field is geared towardthe development of magnetic alloys with MCEs, and phase transitions temperatures suitable forhydrogen liquefaction from Room temperature down to 20 K.Deptt. Of Mechanical Engineering (Vit-east, Jaipur) Magnetic Refrigeration 41
  44. 44. 16.2 Potential Advantages : -The potential advantages of magnetic refrigeration bare valid in comparison with the directevaporation 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 air- conditioning and refrigeration units in automobiles.Deptt. Of Mechanical Engineering (Vit-east, Jaipur) Magnetic Refrigeration 42
  45. 45. 17 17. DISADVANTAGESOn 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.Deptt. Of Mechanical Engineering (Vit-east, Jaipur) Magnetic Refrigeration 43
  46. 46. 18 18. CURRENT AND FUTURE USESThere are still some thermal and magnetic hysteresis problems to be solved for these first-orderphase transition materials that exhibit the MCE to become really useful; this is a subject ofcurrent 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 iscurrently being explored to produce better refrigeration techniques, especially for use inspacecraft. This technique is already used to achieve cryogenic temperatures in the laboratorysetting (below 10K). As an object displaying MCE is moved into a magnetic field, the magneticspins align, lowering the entropy. Moving that object out of the field allows the object to increaseits entropy by absorbing heat from the environment and disordering the spins. In this way, heatcan be taken from one area to another. Should materials be found to display this effect near roomtemperature, refrigeration without the need for compression may be possible, increasing energyefficiency. In addition, magnetic refrigeration could also be used in domestic refrigerators. In 2006, aresearch 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 magneticrefrigeration. This has made the use of the expensive material gadolinium redundant, and madethe creation of domestic magnetic refrigerators possible. The use of this technology for domesticrefrigerators though is very remote due to the high efficiency of current Vapor-compressionrefrigeration in the range of 60% of Carnots efficiency. Gas molecules are responsible for heattransfer, they absorb heat in the inner side of the refrigerator by expanding and release this heatin the outside by condensing. The work provided to do this work is a cheap and highly efficientcompressor, driven by an electric motor that is more than 80% efficient. This technology couldeventually compete with other cryogenic heat pumps for gas liquefaction purposes.Deptt. Of Mechanical Engineering (Vit-east, Jaipur) Magnetic Refrigeration 44
  47. 47. 19 19. CASE STUDYT. 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 MaterialsScience, Tsukuba Magnet Laboratory ,Tsukuba, Ibaraki, 305-0003, Japan have constructed aActive Magnetic Regenerative(AMR) cycle for liquefaction of hydrogen. The magnetic refrigerator model they have constructed is based on a multistage activemagnetic regenerative (AMR) cycle. In their model, an ideal magnetic material with constantmagneto caloric effect is employed as the magnetic working substance. The maximum appliedmagnetic field is 5T, and the liquid hydrogen production rate is 0.01t/day. Starting from liquidnitrogen temperature (77K), it is assumed that four separate four stages of refrigeration areneeded to cool the hydrogen. The results of the simulation show that the use of a magneticrefrigerator for hydrogen liquefaction is possibly more than the use of conventional liquefactionmethods. In general, they have found that, it is helpful to pre cool hydrogen prior to liquefactionusing a cryogenic liquid such as Liquid nitrogen (LN) or liquid natural gas (LNG).Therefore, wechose three system configurations to analyze with our numerical simulation. In the first case, thesupplied hydrogen is pre cooled by the AMRR only. In this case it is assumed that the magneticrefrigeration system pre cools the hydrogen from 300 K to 22 K using approximately 7-9 stagesof AMRR. In the second case, the supplied hydrogen is pre cooled from 300 K to 77 K by LNand 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 bestperformance was achieved by a combined CMR plus a 3-stage AMRR with LN pre cooling. Ithad a total work input of 3.52 kW and had a liquefaction efficiency of 46.9 %. This providespromise that magnetic refrigeration systems may be able to achieve higher efficiency thanconventional liquefaction methodsDeptt. Of Mechanical Engineering (Vit-east, Jaipur) Magnetic Refrigeration 45
  48. 48. 20 20. CONCLUSIONIf we say future perspectives of room temperature Magnetic Refrigeration; It can be seen fromthe earlier Description that main progresses have been made in America. However, with thecontinual phasic progresses of Room temperature magnetic refrigeration, the whole world Hasaccelerated in the research. Nevertheless, it is notable that main work is concentrated Oninvestigations 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 greatperformance difference between Magnetic refrigerator and vapor compression refrigerator inTerms of cooling capacity and temperature span. The number of reserach papers puplished.Thenumber 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(fexsi1- X)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.Deptt. Of Mechanical Engineering (Vit-east, Jaipur) Magnetic Refrigeration 46
  49. 49. 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 BrodrickDeptt. Of Mechanical Engineering (Vit-east, Jaipur) Magnetic Refrigeration 47

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