Sr.No Index Page No1 Introduction 22 Principle 33 Magnetic Refrigeration System 54 Working of the system 95 Latest in system 146 Comparison 177 Challenges Ahead For MRS 228 Application’s 239 Conclusion 2410 References 25
Introduction:- Refrigeration can be defined simply as ‘the process of removing heat from abody to maintain the temperature of the body below that of that of its surrounding’.The science of refrigeration utilizes several methods for providing low temperatures.Everybody is familiar with the vapour compression cycle, which is to date the mostpopular cycle, used for refrigeration, both for industrial & commercial purpose. However there are various limitations in using vapour compression system.The major drawback of the vapour compression system is that it requires acompressor to compressor to compress a large volume of refrigerant vapour whichrequires a large power for its operation. In addition it has poor COP as compared withthe Carnot cycle, environmental hazards like Global warming, limit to the lowesttemperature reached as its drawbacks. Hence we have to continuously look foralternative methods for refrigeration.A large research is going on non-conventional refrigeration systems to produce verylow temperatures which includes Thermo-electric refrigeration, Pulse tuberefrigeration, Vortex tube refrigeration etc. MAGNETIC REFRIGERATION is one of such techniques, whichpromises to be of practical importance. Even though the concept is still into research,20 years down the line we can expect it to be widely used.
2. Principle behind Magnetic Refrigeration:- Magnetic refrigeration is based on the "Magnetocaloric Effect"; the ability ofsome metals to heat when magnetized and cool when removed from the magneticfield. Using these materials as refrigerants provides an environmentally friendlyalternative to the volatile liquid chemicals, such as chlorofluorocarbons andhydrochlorofluorocarbons, which are used in traditional vapour-cycle coolingsystems.2.1 MAGNETO-CALORIC EFFECT :- . Magnetocaloric effect is defined as the response of a solid to an appliedmagnetic field which is apparent as a change in its temperature. This effect is obeyedby all transition metals and lanthanide-series elements. When a magnetic field isapplied, these metals, known as ferromagnets, tend to heat up. As heat is applied, themagnetic moments align. When the field is removed, the ferromagnet cools down asthe magnetic moments become randomly oriented. When a strong magnetic field is applied to the magnetocaloric material, themagnetic moments of its atoms become aligned, making the system moreordered.When the strong magnetic field is removed, the party is forced to cool down.The magnetic moments return to their random directions, entropy increases and thematerial cools. Upon the removal of a magnetic field from a material, the resultingreduction in magnetic spin alignment represents an increase in the materials spinentropy (delta S). If the field reduction is performed adiabatically so that the totalentropy change is zero, then the increased spin entropy is offset by an equal decreasein lattice entropy, as reflected by a decrease in the temperature of the material. Thisdelta T is called the ‘magnetocaloric effect’
2.2 ORDERING TEMPERATURE: The temperature at which most of the change in magnetic entropy occurs isknown as the materials ordering temperature or its Curie point. This is the pointwhere the material changes from being ferromagnetic to paramagnetic, and the fartheraway from this point the weaker the magnetocaloric effect. The useful portion of themagnetocaloric effect usually spans about 25 degrees C (77 F) on either side of thematerials Curie temperature. Therefore, in order to span a wide temperature range, arefrigerator must contain several different coolants arranged according to theirdiffering ordering temperatures Hence it is important to know whether we can adjust the useful range of themagnetocaloric effect to create a particular temperature. In other words similar to theconventional system, where given a particular evaporator temperature we select asuitable refrigerant, here also we need to have materials with varying temperaturerange of the magnetocaloric effect.2.3 GADOLINIUM AND ITS ALLOYS: Since the discovery of the magnetocaloric effect in pure iron by E.Warburg in1881, it has been measured experimentally on many magnetic metals and compounds.Gadolinium, a rare-earth metal, exhibits one of the largest known magnetocaloriceffects. It was used as the refrigerant for many of the early magnetic refrigerationdesigns. The problem with using pure gadolinium as the refrigerant material is that itdoes not exhibit a strong magnetocaloric effect at room temperature. More recently,however, it has been discovered that arc-melted alloys of gadolinium, silicon, andgermanium are more efficient at room temperature. Gschneidner and Pecharsky found that they could tune the operatingtemperature (gradually lower the Curie point) of a gadolinium silicide compound(Gd5Si4) by substituting germanium (Ge) for silicon. This resulted in a newcompound, Gd5Si2Ge2, which has a magnetocaloric effect about twice as large asgadolinium alone.
3. Magnetic Refrigeration System:- With this background of the principal behind the system, lets take a look atthe schematic diagram of the theoretical magnetic refrigeration system & its vapourcompression counterpart. The conventional vapour compression system makes use of a compressor, twoheat exchangers- evaporator & condenser, a throttling device. The refrigerant picks upheat from the space to be refrigerated in the evaporator where it is converted intovapour state. This vapour then passes through the compressor where its pressure &temperature is increased. Refrigerant then gives out its heat in a condenser & getsconverted into a liquid. The throttling device is used to reduce the pressure of therefrigerant to the evaporator pressure. As compared with this the magnetic system does away with the compressor.Instead it makes use of magnets, either permanent or superconducting, to effect achange in magnetic field. The CFC or HFC refrigerant in the conventional system isreplaced by a working substance i.e. a magneto-caloric material. The two heatexchangers are off course still present to effect heat exchange between workingmaterial & a heat transfer fluid. As before in the cold heat exchanger the working substance picks up heat fromthe space to be refrigerated. Then the working substance is brought into a strongmagnetic field or it is magnetised so that due to magneto-caloric effect its temperatureis increased. Working substance then gives out its heat to the heat transfer fluid in ahot heat exchanger. The magnetic field is then reduced, thereby decreasing itstemperature again using the magneto-caloric effect, so that it can pick up heat in acold heat exchanger. In the conventional system compressor is used to increase mainly thetemperature of the refrigerant so that it can exchange heat with the atmospheric air.The throttling device is used to reduce this pressure to evaporator level. In themagnetic system this is achieved by making use magneto-caloric effect. Thus thesystem can do away with both compressor & throttling device.
MAGNETIC REFRIGERATION SYSTEM
3.1 COMPARISON OF T-S DIAGRAMS: Now, let’s compare the T-S charts for conventional & magnetic system. VAPOUR COMPRESSION SYSTEM MAGNETIC REF. SYSTEMFig. 3:- T-S chart for Vapour Compression & Magnetic Refrigeration System. For the two systems the different processes shown on the chart are as follows- a) For Vapour Compression System b) For Magnetic Ref. System 1-2s Non isentropic Compression 1-2 Isentropic temperature rise in in a compressor. high magnetic field, 2s-a-3 Isobaric Condensation in 2-3 Isothermal heat exchange in Condenser, hot heat exchanger, 3-4 Isenthalpic pressure reduction 3-4 Isentropic temperature fall in in throttling device, low magnetic field, 4-1 Isobaric Evaporation in 4-1 Isothermal heat exchange in Evaporator. Cold heat exchanger.
For comparison purpose the temperature limits for both systems are taken assame. As can be seen from the chart the compression process in a vapour compressionis never isentropic. An isentropic process is believed to be the most efficient path forcarrying out any process. This is because entropy is a property of the system, whichmeasures the disorder in a system. Thus higher the amount of disorder in a systemmore will be its entropy. For higher efficiency we need minimum disorder in systemi.e. minimum entropy. To have minimum entropy it is necessary to carry out a process in a reversiblemanner i.e. the system must be able to be restored to its original state by aninfinitesimal change in its parameter. Under these conditions, the entropy generation,which is the sum of entropy of the system & entropy of the universe, is zero. During compression process in a vapour compression system there are manyirreversibilities involved like friction, heat exchange of the hot refrigerant with thesurrounding air, which increases the entropy of the system. Consequently, the processis not the most efficient process & energy is wasted. As compared with this in a magnetic system the process of increasingtemperature of the working substance is completely reversible, since magnetocaloriceffect is entirely reversible. This is because bringing the material out of the magneticfield can lower the temperature of the magnetocaloric salt. As a result of this theentropy generation during both processes 1-2 & 3-4 is zero. Thus, the cycleapproaches the Carnot cycle, which is believed to be the most efficient cycle.As a result of this, even from c.o.p. point of view, the new system comes as a goodsubstitute for the conventional system.
4.2 WORKING OF THE SYSTEM As said earlier the heat transfer fluid for the magnetic refrigeration system is aliquid alcohol-water mixture. The mixture used in the design consists of 60 % ethanoland 40 % water. This mixture has a freezing point of –40°F, assuring that the mixturedoes not freeze at the set operating temperatures. This heat transfer fluid is cheaperthan traditional refrigerants and also eliminates the environmental damage producedfrom these refrigerants.
The process flow diagram for the magnetic refrigeration system is shown inFigure 4. The fluid first passes through the hot heat exchanger, which uses air totransfer heat to the atmosphere. The fluid then passes through the copper platesattached to the non-magnetized cooler magnetocaloric beds and loses heat. A fanblows air past this cold fluid into the freezer to keep the freezer temperature atapproximately 0°F. The heat transfer fluid then gets heated up to 80°F as it passesthrough the copper plates adjoined by the magnetized warmer magnetocaloric beds,where it continues to cycle around the loop. However, the magnetocaloric bedssimultaneously move up and down, into and out of the magnetic field. The secondposition of the beds is shown in Figure 5. The temperature of the refrigerator sectionis kept around 39°F. The temperature of the fluid throughout the cycle ranges from –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,E-102, where it absorbs the excess heat from the freezer. This fluid leaves the freezerat 0°F. The warm fluid then flows through the opposite magnetized set of beds, whereit is heated up to 80°F. This hot stream is now cooled by room temperature air in thehot heat exchanger, E-101, to 70°F. The cycle then repeats itself every three secondsafter the beds have switched positions. Copper tubing is used throughout the loop andin the two heat exchangers. The two sets of beds, B-101 and B-102, contain the small spheres ofmagnetocaloric material. The size of the beds resembles that of half of a soda can.The beds are alternated in and out of the magnetic field using a chain and sprocketdrive shaft. The drive shaft rotates the beds back and forth while still keeping them incontact with the heat transfer plates.
Fig. 6:- The Actual Set-up of the system
The rate of heat removal from the refrigerated space can be directly calculatedby knowing the temperature of the heat transfer fluid at entry & exit of the cold heatexchanger. The critical part is the calculation of the magnetic work performed on theGd beds. This work rate is found out by plotting the Temperature-Entropy (T-S)diagram for Gadolinium. For this one is required to find out the temperature ofGadolinium at various points in the cycle which is accomplished with the help ofthermocouple. Once temperatures are found out then the cycle is plotted on the T-Schart. The work rate is then found by finding the area of the cycle on the T-S diagram,which is done with the help of integration. Here the nos. 1 to 5 indicate the cycle employing various volumes of Gd saltor in other words these are the cycles that various volumes of Gd salt undergo in amagnetic cycle. In the experiment, as said earlier, a magnetocaloric bed is used to produce thecooling effect. This bed can be divided into 5 volumes which are approximatelyequal, but undergo different cycle (i.e. have different temperatures). This can beshown in the actual set-up as shown diagrammatically in the following fig. As shownthe magnetocaloric bed is a cylinder of packed Gd salt of about 2.5 cm in diameter &16 cm in height. Once COP is calculated another important parameter of the system "FigureOf Merit (FOM)" can be calculated. As already stated the ideal cycle for anyrefrigeration system is the reversed Carnot cycle since it doesnt involve anyirreversibility or entropy generation. But due to some practical difficulties the systemcan not be actually realised in practice. However the Carnot cycle stands as a benchmark for all practical cycles. Hence the performance of all practical cycles is compared with a reversedCarnot cycle working under same temperature limits. Figure of merit (FOM) givesthis comparison. It is nothing but the ratio of the COP of the actual system to the COPof a reversed carnot cycle working under the same temperature limits of evaporator &condenser.
Thus, mathematically, Figure Of Merit, FOM = (COP)actual (COP)carnot FOM is usually expressed as a % of Carnot. For example a FOM of 30%means that the COP of actual system is 3 for a Carnot COP of 10 working betweensame temperature limits.Fig. 8:- Details of Gadolinium packed regenerative bed used in the experimentalsetup.
5. The Latest In Magnetic Refrigeration:- On Tuesday, September 18, 2001, the worlds first successful permanentmagnet, room temperature, magnetic refrigerator became operational at theAstronautics Corporation of America Technology Center in Madison WI. Thismagnetic refrigerator provides a cooling range similar to a household air conditionerwithout the use of ozone depleting or global warming gases deemed harmful to theenvironment. The magnetic refrigerator uses a material based on gadolinium, a metallicelement that exhibits a large magnetocaloric effect. The material is alternatelymagnetized and demagnetized by rotating a wheel containing the material through amagnetic field. The process is much more efficient than typical vapor cyclerefrigeration systems in use today. The heat transfer fluid used in the prototype is water. Environmentally harmfulgases are not used in the magnetic refrigerator.Previously built magnetic refrigerators used in laboratory demonstrations requiredlarge superconducting magnets. The new Astronautics magnetic refrigerator uses apermanent magnet, which results in a compact package that runs virtually silent andand vibration free, proving the viability of a small magnetic refrigerator. The systemcan be shown diagrammatically as follows:-
Analogy between magnetic refrigeration and vapor cycle or conventionalrefrigeration. H = externally applied magnetic field; Q = heat quantity; P = pressure;ΔTad = adiabatic temperature variationThe cycle is performed as a refrigeration cycle, analogous to the Carnot cycle, and canbe described at a starting point whereby the chosen working substance is introducedinto a magnetic field, i.e., the magnetic flux density is increased. The workingmaterial is the refrigerant, and starts in thermal equilibrium with the refrigeratedenvironment. Adiabatic magnetization: A magnetocaloric substance is placed in an insulated environment. The increasing external magnetic field (+H) causes the magnetic dipoles of the atoms to align, thereby decreasing the 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).
Isomagnetic enthalpic transfer: This added heat can then be removed (-Q) by a fluid or gas — gaseous or liquidhelium, for example. The magnetic field is held constant to prevent the dipoles fromreabsorbing the heat. Once sufficiently cooled, the magnetocaloric substance and thecoolant are separated (H=0). Adiabatic demagnetization: The substance is returned to another adiabatic (insulated) condition so the total entropy remains constant. However, this time the magnetic field is decreased, the thermal energy causes the magnetic moments to overcome the field, and thus the sample cools, i.e., an adiabatic temperature change. Energy (and entropy) transfers from thermal entropy to magnetic entropy (disorder of the magnetic dipoles). Isomagnetic entropic transfer: The magnetic field is held constant to prevent the material from heating back up. The material is placed in thermal contact with the environment being refrigerated. Because the working material is cooler than the refrigerated environment (by design), heat energy migrates into the working material (+Q)..
Comparison Of Magnetic Refrigeration System With TheConventional Vapour Compression System:- Whenever a new technology comes up & tries to replace an existing,established technology, it has to naturally offer some advantages. In case of MagneticRefrigeration System, the magnetic refrigeration system needs to compete with themost widely used technique of Vapour Compression System. So lets see whatadvantage Magnetic Refrigeration offers as compared with the conventional system .Advantages:-1. Environmental Friendly Technology:- The most important advantage offered by magnetic system is that it does awaywith the refrigerants present in the vapour compression system which are mainlyCholoroflurocarbons & Hydroflurocarbon (CFCs & HFCs). Most of the domestic &industrial refrigerators & air-conditioners employ refrigerants such as R12, R22 etc.These refrigerants contain Chlorine, which is responsible for the destruction of Ozonelayer. This ozone layer restricts the passage of Ultra-violet (UV) rays towards thesurface of the earth. Thus, its destruction is leading to ill-effects such as GlobalWarming i.e. increase in the average temperature of the earth surface. Hence many countries around the world have decided to regulate the use ofsuch refrigerants in the refrigerating units. All these have agreed on following someregulations known as "Montreal Protocol". This calls for the refrigerants like R11.R12, R113 to be phased out by 2000 AD & refrigerant R22 to be phased out by 2030AD in developed countries. As against this the magnetic system utilises magnetocaloric material & a heattransfer fluid such as water or water + ethanol which is environmentally friendly &does not have Ozone Depleting Potential (ODP). Hence the ban on the refrigerantsused in vapour compression system makes magnetic refrigeration an automatic choicefor future refrigeration system. Another disadvantage of the refrigerants in the conventional system is that thecost of these refrigerants is quite high. Hence accidental leakage of refrigerant meansa great financial loss. In magnetic system, since the refrigerant is solid Gd spheres
there is no such danger of refrigerant escaping to atmosphere & subsequently noreplacement cost. Yet another cost involved with the conventional system is the cost involved inthe environmental cleanup/restoration and protection costs. The elimination ofharmful chemicals will considerably reduce environmental cleanup/restoration andprotection costs for federal and local governments.2. High Thermodynamic Efficiency:- Another important advantage offered by magnetic system is the highthermodynamic efficiency as compared with the conventional system. Fig. 3 shows the T-S diagram for both the conventional & magnetic system.As seen from the fig. the magnetic system approximates a reversed Carnot cycle muchbetter than a conventional system. The system has practically very little entropygeneration or irreversibility. Due to this the work input required to produce a desiredcooling effect is much less. As against this the conventional system involves a finite amount of entropygeneration or irreversibility due to various reasons such as friction, heat exchange ofhot refrigerant with the atmosphere & walls of compressor etc. Even with the best ofthe designs it is not possible to reduce this entropy generation to zero. Subsequentlythe work input required is higher to overcome all these irreversibilities. Naturally theCOP of conventional system is much lower as compared to the magnetic system. Withthe magnetic system a COP of 15 has been reached in the setup developed by AmesLab. & ACA. Recent research has sown an energy efficiency of 60 % is possible withmagnetic technology, while conventional refrigerators are only about 20-40%efficient.3. Silent, Vibration Free Design:- One of the primary devices used in a conventional system is a compressor.This compressor is used to compress the vapour refrigerant to increase itstemperature. However, the presence of this device brings a few disadvantages to the
conventional system such as the noise & vibrations generated during the working ofcompressor. In a magnetic system this component is absent & is replaced by a magnetwhose operation does not involve any noise or vibration. Here there is no need tophysically compress the refrigerant. Due to this a magnetic system can run almostnoiseless & vibrationless. This makes the design of a refrigerating system much moreeasier. These aspects of a refrigerating or air-conditioning system are importantmainly in applications such as Automobiles.4. Lowest Temperature That Can Be Reached:- Leaving aside the environmental & cost savings, the area where the magneticrefrigeration system leaves the conventional system far behind is the lowesttemperature that can be reached. This is particularly important in applications such asliquefaction of gases such as Hydrogen, Nitrogen. With the continuing shortage offossil fuels energy sources such as liquid Hydrogen & Nitrogen are becomingincreasingly important. However the liquefaction of this gases requires maintainingquite low temperature such as 20 K. Now in a conventional vapour compression system maintaining a particulartemperature is governed by the boiling point of the refrigerant. With the vapourcompression system we can surely have a refrigerant which can boil at 20 K & extractheat at that temperature. However it is not possible to have a single refrigeration cycleoperating between 20 K & room temperature. Hence we have to go for cascading ofsystems to achieve this low temperature. Thus today it requires sometimes as many as15 stages to achieve a temperature of 20 K. With the inherent low efficiency of theconventional system this means considerable wastage of energy & the system can noteconomically produce less than 5 tons/day of Hydrogen. Another drawback of theconventional system is that even with cascading of systems the lowest possibletemperature in conventional system is restricted to 1 K. As against this magnetic refrigeration system has historically aimed atcryogenic or low temperature application. It is claimed that temperatures as low as0.001 K can be achieved with the magnetic refrigeration system. Newer systems arebeing invented which aim at one shot or single stage process for producing
temperatures such as 20 K. With the highly efficient magnetic systems the productionof liquid gases promises to be cheaper & it is believed that with magnetic system itwill be possible to economically produce less than 5 tons of Hydrogen per day.5. Overall Cost Saving:- As discussed in the preceding discussion the magnetic refrigeration systemproves to be highly energy efficient. In large scale commercial applications ofrefrigeration efficiency improvement of even 10% can mean a lot of cost saving.Magnetic refrigeration has also been investigated for the large scale air conditioningmarket. Studies have shown that a 300 ton magnetocaloric based air conditioner couldhave an efficiency of 0.43 kW/ton, after all losses were considered. This represents a22% decrease in energy use over a typical centrifugal chiller with an efficiency of0.55 kW/ton. Besides this there are various other noteworthy benefits of magneticrefrigeration system in terms of cost savings such as:- The elimination of harmful chemicals will considerably reduce environmental cleanup/restoration and protection costs for federal and local governments. This spending reduction will result in lower taxes. By lowering the energy consumption in refrigeration, freezing and air conditioning systems for the food-production industry and grocery stores, the costs of preparing, storing and selling food will be reduced. This will mean lower monthly grocery bills for consumers & overall reduction in prices of foodstuff. Household energy costs will be reduced because of the lower energy consumption of home refrigerators and air conditioners. Commercialization of electric vehicles should reduce every country’s dependence on imported oil and other fossil fuels, resulting in decreased demand and lower energy costs for transportation. With electric vehicles becoming a practical technology this promises to be a major advantage favoring magnetic system. Magnetic refrigeration systems have fewer moving parts than traditional vapor- cycle cooling systems, increasing their reliability. Magnetic refrigeration systems will have fewer breakdowns, longer service life and will virtually eliminate the need
to replenish lost refrigerant. This will mean a significant reduction in service/replacement costs for refrigeration and air-conditioning systems. With all above advantages the rupee cost savings are difficult to determine atthis time, but the energy efficiency of magnetic refrigeration will reduce energy costsin refrigeration and air-conditioning systems by as much as 30%. Although magneticrefrigerators and air conditioners will initially be more expensive than traditionalvapor-cycle technology units, the projected energy savings should enable consumersto bridge the difference in five years or sooner. After that, the energy savings will bemoney in the bank.
7. Challenges Ahead For Magnetic Refrigeration System:- Despite all its promise, magnetic refrigeration technology still has hurdles toovercome if it is to ever give conventional vapor-based technology a run for themoney. A few of these hurdles are as follows:- Small Temperature Spans:- When it comes to a small temperature span, such as the range of temperature in cooling a home or car, the conventional refrigeration system still leads the race. Only for large temperature spans, such as those associated with liquefying gases, do small increases in efficiency make a big money-saving difference. Size Of The System:- An important consideration in applications as domestic refrigerators, car air-conditioners is the size of the system. The first successful magnetic refrigerator developed by Ames lab & ACA makes use of superconducting magnet, which makes the system bulky & big in size. Though the permanent magnet variety has been developed, it is still under testing & the presence of big sized bulky magnets makes the system size quite big. Cost Of The System:- With all the cost saving in running a magnetic system, the capital cost of a magnetic refrigeration system promises to be quite high. Thus, the system may prove to be costly. Secondly the system has to really deliver performance under actual condition similar to test condition. Otherwise this technology will loose its important advantage of cost saving. High Reliability Of The Conventional System:- Besides the above the other challenge faced by the technology are the high reliability & popularity due to widespread use of vapour compression systems. Vapour compression systems have been in use for many years now & have proved to be most popular method of refrigeration. Hence eliminating their use totally will take considerable technological advance & strict implementation of Montreal Protocol by all the countries. Magnetic refrigeration systems will have to prove that they are really reliable under normal use. Thus in future the extensive use of magnetic systems will be subject to howwell can the technology sustain growth in various technical areas such as magnets,magnetocaloric materials, heat exchangers & other circuitry.
8. Areas Of Application:- With all its promise we can hope to see the use of magnetic refrigerationsystems in the following applications:- Liquefaction Of Gases such as Hydrogen, Nitrogen etc., Re-liquefaction of helium in hospital MRI (magnetic resonance imaging) , Large Scale refrigeration applications such as food-storage, Industrial air-conditioning applications such as large restaurants, large shopping complex, commercial establishments, hospitals etc., Industries with specific temperature applications such as paper pulp industry, cloth mills, food industries, cassette industry etc., Low temperature applications such as Cryogenics, Commercial applications such as household refrigerator, Automobile applications such as car air-conditioners especially Electric vehicles. Besides these the technology has a potential to be of practical importance inalmost all applications of refrigeration & air-conditioning.
9. Conclusion:- Magnetic Refrigeration is a clean, environmentally friendly technology, whichreplaces the environmentally hazardous refrigerants in a vapour compression systemwith a magnetocaloric substance & a heat transfer fluid, which are environmentallyfriendly. With the ever increasing concern about environmental hazards it promises tobe a technology of the future. However, before the widespread use of magneticrefrigerators can begin in both industrial & commercial application, the technologyhas to cross a few technical hurdles & prove its worth. But it wont be long before wewill see magnetic refrigerators take over from the conventional vapour compressionsystem in all the fields of application.
10. References:-1. "A Course In Refrigeration & Air-conditioning" by S. C. Arora & S.Domkundwar. Publication:- Dhanpat Rai & Co. (P) Ltd. Seventh Edition.2. "The CRC Handbook Of Thermal Engineering". Editor:- Frank Kreith.3. Visit to:- es.epa.gov/ncer_abstracts/grants/99/sustain/wagner.html4. Visit to:- www.aps.org/BAPSMAR98/abs/S3220.html5. Visit to:- www.lanl.gov/6. Visit to:- www2.cemr.wvu.edu/~wwwche/publications/projects/prod_design/ magnetic_refrigerator.pdf7. Visit to:- www.astronautics.com/PressRelease/Files/MagFrig.PDF8. Visit to:- www.sciencenews.org/20020105/fob2.asp