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Seminar report nitin unde

  1. 1. Sr.No Index Page No 1 Introduction 2 2 Principle 3 3 Magnetic Refrigeration System 5 4 Working of the system 9 5 Latest in system 14 6 Comparison 17 7 Challenges Ahead For MRS 22 8 Application’s 23 9 Conclusion 24 10 References 25
  2. 2. Introduction:- Refrigeration can be defined simply as ‘the process of removing heat from a body 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 most popular 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 a compressor to compressor to compress a large volume of refrigerant vapour which requires a large power for its operation. In addition it has poor COP as compared with the Carnot cycle, environmental hazards like Global warming, limit to the lowest temperature reached as its drawbacks. Hence we have to continuously look for alternative methods for refrigeration. A large research is going on non-conventional refrigeration systems to produce very low temperatures which includes Thermo-electric refrigeration, Pulse tube refrigeration, Vortex tube refrigeration etc. 'MAGNETIC REFRIGERATION' is one of such techniques, which promises 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.
  3. 3. 2. Principle behind Magnetic Refrigeration:- Magnetic refrigeration is based on the "Magnetocaloric Effect"; the ability of some metals to heat when magnetized and cool when removed from the magnetic field. Using these materials as refrigerants provides an environmentally friendly alternative to the volatile liquid chemicals, such as chlorofluorocarbons and hydrochlorofluorocarbons, which are used in traditional vapour-cycle cooling systems. 2.1 MAGNETO-CALORIC EFFECT :- . Magnetocaloric effect is defined as the response of a solid to an applied magnetic field which is apparent as a change in its temperature. This effect is obeyed by all transition metals and lanthanide-series elements. When a magnetic field is applied, these metals, known as ferromagnets, tend to heat up. As heat is applied, the magnetic moments align. When the field is removed, the ferromagnet cools down as the magnetic moments become randomly oriented. When a strong magnetic field is applied to the magnetocaloric material, the magnetic moments of its atoms become aligned, making the system more ordered.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 the material cools. Upon the removal of a magnetic field from a material, the resulting reduction in magnetic spin alignment represents an increase in the material's spin entropy (delta S). If the field reduction is performed adiabatically so that the total entropy change is zero, then the increased spin entropy is offset by an equal decrease in lattice entropy, as reflected by a decrease in the temperature of the material. This delta T is called the ‘magnetocaloric effect’
  4. 4. 2.2 ORDERING TEMPERATURE: The temperature at which most of the change in magnetic entropy occurs is known as the material's ordering temperature or its Curie point. This is the point where the material changes from being ferromagnetic to paramagnetic, and the farther away from this point the weaker the magnetocaloric effect. The useful portion of the magnetocaloric effect usually spans about 25 degrees C (77 F) on either side of the material's Curie temperature. Therefore, in order to span a wide temperature range, a refrigerator must contain several different coolants arranged according to their differing ordering temperatures Hence it is important to know whether we can adjust the useful range of the magnetocaloric effect to create a particular temperature. In other words similar to the conventional system, where given a particular evaporator temperature we select a suitable refrigerant, here also we need to have materials with varying temperature range of the magnetocaloric effect. 2.3 GADOLINIUM AND ITS ALLOYS: Since the discovery of the magnetocaloric effect in pure iron by E.Warburg in 1881, it has been measured experimentally on many magnetic metals and compounds. Gadolinium, a rare-earth metal, exhibits one of the largest known magnetocaloric effects. It was used as the refrigerant for many of the early magnetic refrigeration designs. The problem with using pure gadolinium as the refrigerant material is that it does not exhibit a strong 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. Gschneidner and Pecharsky found that they could tune the operating temperature (gradually lower the Curie point) of a gadolinium silicide compound (Gd5Si4) by substituting germanium (Ge) for silicon. This resulted in a new compound, Gd5Si2Ge2, which has a magnetocaloric effect about twice as large as gadolinium alone.
  5. 5. 3. Magnetic Refrigeration System:- With this background of the principal behind the system, let's take a look at the schematic diagram of the theoretical magnetic refrigeration system & its vapour compression counterpart. The conventional vapour compression system makes use of a compressor, two heat exchangers- evaporator & condenser, a throttling device. The refrigerant picks up heat from the space to be refrigerated in the evaporator where it is converted into vapour state. This vapour then passes through the compressor where its pressure & temperature is increased. Refrigerant then gives out its heat in a condenser & gets converted into a liquid. The throttling device is used to reduce the pressure of the refrigerant 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 a change in magnetic field. The CFC or HFC refrigerant in the conventional system is replaced by a working substance i.e. a magneto-caloric material. The two heat exchangers are off course still present to effect heat exchange between working material & a heat transfer fluid. As before in the cold heat exchanger the working substance picks up heat from the space to be refrigerated. Then the working substance is brought into a strong magnetic field or it is magnetised so that due to magneto-caloric effect its temperature is increased. Working substance then gives out its heat to the heat transfer fluid in a hot heat exchanger. The magnetic field is then reduced, thereby decreasing its temperature again using the magneto-caloric effect, so that it can pick up heat in a cold heat exchanger. In the conventional system compressor is used to increase mainly the temperature 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 the magnetic system this is achieved by making use magneto-caloric effect. Thus the system can do away with both compressor & throttling device.
  6. 6. MAGNETIC REFRIGERATION SYSTEM
  7. 7. 3.1 COMPARISON OF T-S DIAGRAMS: Now, let’s compare the T-S charts for conventional & magnetic system. VAPOUR COMPRESSION SYSTEM MAGNETIC REF. SYSTEM Fig. 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.
  8. 8. For comparison purpose the temperature limits for both systems are taken as same. As can be seen from the chart the compression process in a vapour compression is never isentropic. An isentropic process is believed to be the most efficient path for carrying out any process. This is because entropy is a property of the system, which measures the disorder in a system. Thus higher the amount of disorder in a system more will be its entropy. For higher efficiency we need minimum disorder in system i.e. minimum entropy. To have minimum entropy it is necessary to carry out a process in a reversible manner i.e. the system must be able to be restored to its original state by an infinitesimal 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 many irreversibilities involved like friction, heat exchange of the hot refrigerant with the surrounding air, which increases the entropy of the system. Consequently, the process is not the most efficient process & energy is wasted. As compared with this in a magnetic system the process of increasing temperature of the working substance is completely reversible, since magnetocaloric effect is entirely reversible. This is because bringing the material out of the magnetic field can lower the temperature of the magnetocaloric salt. As a result of this the entropy generation during both processes 1-2 & 3-4 is zero. Thus, the cycle approaches 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 good substitute for the conventional system.
  9. 9. 4.2 WORKING OF THE SYSTEM As said earlier the heat transfer fluid for the magnetic refrigeration system is a liquid alcohol-water mixture. The mixture used in the design consists of 60 % ethanol and 40 % water. This mixture has a freezing point of –40°F, assuring that the mixture does not freeze at the set operating temperatures. This heat transfer fluid is cheaper than traditional refrigerants and also eliminates the environmental damage produced from these refrigerants.
  10. 10. The process flow diagram for the magnetic refrigeration system is shown in Figure 4. The fluid first passes through the hot heat exchanger, which uses air to transfer heat to the atmosphere. The fluid then passes through the copper plates attached to the non-magnetized cooler magnetocaloric beds and loses heat. A fan blows air past this cold fluid into the freezer to keep the freezer temperature at approximately 0°F. The heat transfer fluid then gets heated up to 80°F as it passes through the copper plates adjoined by the magnetized warmer magnetocaloric beds, where it continues to cycle around the loop. However, the magnetocaloric beds simultaneously move up and down, into and out of the magnetic field. The second position of the beds is shown in Figure 5. The temperature of the refrigerator section is 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 freezer at 0°F. The warm fluid then flows through the opposite magnetized set of beds, where it is heated up to 80°F. This hot stream is now cooled by room temperature air in the hot heat exchanger, E-101, to 70°F. The cycle then repeats itself every three seconds after the beds have switched positions. Copper tubing is used throughout the loop and in the two heat exchangers. The two sets of beds, B-101 and B-102, contain the small spheres of magnetocaloric 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 sprocket drive shaft. The drive shaft rotates the beds back and forth while still keeping them in contact with the heat transfer plates.
  11. 11. Fig. 6:- The Actual Set-up of the system
  12. 12. The rate of heat removal from the refrigerated space can be directly calculated by knowing the temperature of the heat transfer fluid at entry & exit of the cold heat exchanger. The critical part is the calculation of the magnetic work performed on the Gd 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 of Gadolinium at various points in the cycle which is accomplished with the help of thermocouple. Once temperatures are found out then the cycle is plotted on the T-S chart. 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 salt or in other words these are the cycles that various volumes of Gd salt undergo in a magnetic cycle. In the experiment, as said earlier, a magnetocaloric bed is used to produce the cooling effect. This bed can be divided into 5 volumes which are approximately equal, but undergo different cycle (i.e. have different temperatures). This can be shown in the actual set-up as shown diagrammatically in the following fig. As shown the 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 "Figure Of Merit (FOM)" can be calculated. As already stated the ideal cycle for any refrigeration system is the reversed Carnot cycle since it doesn't involve any irreversibility or entropy generation. But due to some practical difficulties the system can not be actually realised in practice. However the Carnot cycle stands as a bench mark for all practical cycles. Hence the performance of all practical cycles is compared with a reversed Carnot cycle working under same temperature limits. Figure of merit (FOM) gives this comparison. It is nothing but the ratio of the COP of the actual system to the COP of a reversed carnot cycle working under the same temperature limits of evaporator & condenser.
  13. 13. 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 between same temperature limits. Fig. 8:- Details of Gadolinium packed regenerative bed used in the experimental setup.
  14. 14. 5. The Latest In Magnetic Refrigeration:- On Tuesday, September 18, 2001, the world's first successful permanent magnet, room temperature, magnetic refrigerator became operational at the Astronautics Corporation of America Technology Center in Madison WI. This magnetic refrigerator provides a cooling range similar to a household air conditioner without the use of ozone depleting or global warming gases deemed harmful to the environment. The magnetic refrigerator uses a material based on gadolinium, a metallic element that exhibits a large magnetocaloric effect. The material is alternately magnetized and demagnetized by rotating a wheel containing the material through a magnetic field. The process is much more efficient than typical vapor cycle refrigeration systems in use today. The heat transfer fluid used in the prototype is water. Environmentally harmful gases are not used in the magnetic refrigerator. Previously built magnetic refrigerators used in laboratory demonstrations required large superconducting magnets. The new Astronautics magnetic refrigerator uses a permanent magnet, which results in a compact package that runs virtually silent and and vibration free, proving the viability of a small magnetic refrigerator. The system can be shown diagrammatically as follows:-
  15. 15. Analogy between magnetic refrigeration and vapor cycle or conventional refrigeration. H = externally applied magnetic field; Q = heat quantity; P = pressure; ΔTad = adiabatic temperature variation The cycle is performed as a refrigeration cycle, analogous to the Carnot cycle, and can be described at a starting point whereby the chosen working substance is introduced into a magnetic field, i.e., the magnetic flux density is increased. The working material is the refrigerant, and starts in thermal equilibrium with the refrigerated environment.  Adiabatic magnetization: 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 material's magnetic entropy and heat capacity. Since overall energy is not lost (yet) and therefore total entropy is not reduced (according to thermodynamic laws), the net result is that the item heats up (T + ΔTad).
  16. 16.  Isomagnetic enthalpic transfer: This added heat can then be removed (-Q) by a fluid or gas — gaseous or liquid helium, for example. The magnetic field is held constant to prevent the dipoles from reabsorbing the heat. Once sufficiently cooled, the magnetocaloric substance and the coolant are separated (H=0).  Adiabatic demagnetization: The substance is returned to another adiabatic (insulated) condition so the total entropy remains constant. However, this time the magnetic field is decreased, the thermal energy causes the 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). .
  17. 17. Comparison Of Magnetic Refrigeration System With The Conventional 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 Magnetic Refrigeration System, the magnetic refrigeration system needs to compete with the most widely used technique of Vapour Compression System. So let's see what advantage 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 away with the refrigerants present in the vapour compression system which are mainly Choloroflurocarbons & Hydroflurocarbon (CFC's & HFC's). 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 Ozone layer. This ozone layer restricts the passage of Ultra-violet (UV) rays towards the surface of the earth. Thus, it's destruction is leading to ill-effects such as Global Warming i.e. increase in the average temperature of the earth surface. Hence many countries around the world have decided to regulate the use of such refrigerants in the refrigerating units. All these have agreed on following some regulations 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 2030 AD in developed countries. As against this the magnetic system utilises magnetocaloric material & a heat transfer fluid such as water or water + ethanol which is environmentally friendly & does not have Ozone Depleting Potential (ODP). Hence the ban on the refrigerants used in vapour compression system makes magnetic refrigeration an automatic choice for future refrigeration system. Another disadvantage of the refrigerants in the conventional system is that the cost of these refrigerants is quite high. Hence accidental leakage of refrigerant means a great financial loss. In magnetic system, since the refrigerant is solid Gd spheres
  18. 18. there is no such danger of refrigerant escaping to atmosphere & subsequently no replacement cost. Yet another cost involved with the conventional system is the cost involved in the environmental cleanup/restoration and protection costs. The elimination of harmful chemicals will considerably reduce environmental cleanup/restoration and protection costs for federal and local governments. 2. High Thermodynamic Efficiency:- Another important advantage offered by magnetic system is the high thermodynamic 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 much better than a conventional system. The system has practically very little entropy generation or irreversibility. Due to this the work input required to produce a desired cooling effect is much less. As against this the conventional system involves a finite amount of entropy generation or irreversibility due to various reasons such as friction, heat exchange of hot refrigerant with the atmosphere & walls of compressor etc. Even with the best of the designs it is not possible to reduce this entropy generation to zero. Subsequently the work input required is higher to overcome all these irreversibilities. Naturally the COP of conventional system is much lower as compared to the magnetic system. With the magnetic system a COP of 15 has been reached in the setup developed by Ames Lab. & ACA. Recent research has sown an energy efficiency of 60 % is possible with magnetic 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 it's temperature. However, the presence of this device brings a few disadvantages to the
  19. 19. conventional system such as the noise & vibrations generated during the working of compressor. In a magnetic system this component is absent & is replaced by a magnet whose operation does not involve any noise or vibration. Here there is no need to physically compress the refrigerant. Due to this a magnetic system can run almost noiseless & vibrationless. This makes the design of a refrigerating system much more easier. These aspects of a refrigerating or air-conditioning system are important mainly in applications such as Automobiles. 4. Lowest Temperature That Can Be Reached:- Leaving aside the environmental & cost savings, the area where the magnetic refrigeration system leaves the conventional system far behind is the lowest temperature that can be reached. This is particularly important in applications such as liquefaction of gases such as Hydrogen, Nitrogen. With the continuing shortage of fossil fuels energy sources such as liquid Hydrogen & Nitrogen are becoming increasingly important. However the liquefaction of this gases requires maintaining quite low temperature such as 20 K. Now in a conventional vapour compression system maintaining a particular temperature is governed by the boiling point of the refrigerant. With the vapour compression system we can surely have a refrigerant which can boil at 20 K & extract heat at that temperature. However it is not possible to have a single refrigeration cycle operating between 20 K & room temperature. Hence we have to go for cascading of systems to achieve this low temperature. Thus today it requires sometimes as many as 15 stages to achieve a temperature of 20 K. With the inherent low efficiency of the conventional system this means considerable wastage of energy & the system can not economically produce less than 5 tons/day of Hydrogen. Another drawback of the conventional system is that even with cascading of systems the lowest possible temperature in conventional system is restricted to 1 K. As against this magnetic refrigeration system has historically aimed at cryogenic or low temperature application. It is claimed that temperatures as low as 0.001 K can be achieved with the magnetic refrigeration system. Newer systems are being invented which aim at one shot or single stage process for producing
  20. 20. temperatures such as 20 K. With the highly efficient magnetic systems the production of liquid gases promises to be cheaper & it is believed that with magnetic system it will 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 system proves to be highly energy efficient. In large scale commercial applications of refrigeration efficiency improvement of even 10% can mean a lot of cost saving. Magnetic refrigeration has also been investigated for the large scale air conditioning market. Studies have shown that a 300 ton magnetocaloric based air conditioner could have an efficiency of 0.43 kW/ton, after all losses were considered. This represents a 22% decrease in energy use over a typical centrifugal chiller with an efficiency of 0.55 kW/ton. Besides this there are various other noteworthy benefits of magnetic refrigeration 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
  21. 21. 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 at this time, but the energy efficiency of magnetic refrigeration will reduce energy costs in refrigeration and air-conditioning systems by as much as 30%. Although magnetic refrigerators and air conditioners will initially be more expensive than traditional vapor-cycle technology units, the projected energy savings should enable consumers to bridge the difference in five years or sooner. After that, the energy savings will be money in the bank.
  22. 22. 7. Challenges Ahead For Magnetic Refrigeration System:- Despite all its promise, magnetic refrigeration technology still has hurdles to overcome if it is to ever give conventional vapor-based technology a run for the money. 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 it's 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 how well can the technology sustain growth in various technical areas such as magnets, magnetocaloric materials, heat exchangers & other circuitry.
  23. 23. 8. Areas Of Application:- With all it's promise we can hope to see the use of magnetic refrigeration systems 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 in almost all applications of refrigeration & air-conditioning.
  24. 24. 9. Conclusion:- Magnetic Refrigeration is a clean, environmentally friendly technology, which replaces the environmentally hazardous refrigerants in a vapour compression system with a magnetocaloric substance & a heat transfer fluid, which are environmentally friendly. With the ever increasing concern about environmental hazards it promises to be a technology of the future. However, before the widespread use of magnetic refrigerators can begin in both industrial & commercial application, the technology has to cross a few technical hurdles & prove it's worth. But it won't be long before we will see magnetic refrigerators take over from the conventional vapour compression system in all the fields of application.
  25. 25. 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.html 4. Visit to:- www.aps.org/BAPSMAR98/abs/S3220.html 5. Visit to:- www.lanl.gov/ 6. Visit to:- www2.cemr.wvu.edu/~wwwche/publications/projects/prod_design/ magnetic_refrigerator.pdf 7. Visit to:- www.astronautics.com/PressRelease/Files/MagFrig.PDF 8. Visit to:- www.sciencenews.org/20020105/fob2.asp

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