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a seminar report magnetic refrigeration a seminar report magnetic refrigeration Document Transcript

  • 1 A Seminar On “MAGNETIC REFRIGERATION” By MR. HARDIK N KOTHIYA Under The Guidance Of Prof. J. R. MAHAJAN Submitted In Partial Fulfillment of the Requirement For Bachelor of Engineering (Mechanical)Degree of University of Pune Department of Mechanical Engineering Late G.N. SapkalCollege of Engineering, Anjaneri, Nashik-422212 2013-2014
  • 2 Kalyani Charitable Trust’s Late G. N. Sapkal College of Engineering Sapkal Knowledge Hub, Kalyani Hills, Anjaneri, Trimbakeshwar Road, Nashik – 422 212, Maharashtra State, India CERTIFICATE This is to certify that Mr. HARDIK N KOTHIYAhas successfully completed his Seminaron the topic“MAGNETIC REFRIGERATION”, under the able guidance of Prof. J. R. MAHAJANtowards the partial fulfillment ofThird YearofMechanical Engineering as laid down byUniversity of Pune during academic year 2013-14. Prof. Prof. T.Y. Badgujar [Seminar Guide] [ H.O.D. Mechanical ] Dr. Basavaraj S. Balapgol [Examiner] Principal
  • 3 CONTENT ACKNOWLEDGEMENT ABSTRACT INDEX Sr. No. Description Page No. 1 Introduction 7 2 History 8 3 Refrigeration 9 3.1 Magnetic Refrigeration 9 4 Objective Of Magnetic Refrigeration 10 5 Magneto-caloric Effect 10 6 Working Of Magnetic Refrigeration 12 6.1 Magnetic Refrigeration System 12 6.2 Refrigerator’s Configuration 13 7 Comparison Between Magnetic Refrigeration & Conventional Refrigeration 14 8 Components 16 9 Application 17 9.1 A Rotary AMR Liquefier 17 9.2 Future Application 17 10 Techinical Benefits 18 11 Advantages 18 12 Disadvantages 19 13 Current & Future Uses 20 14 Conclusion 21 15 Reference 21
  • 4 FIGURE INDEX FIGURE NO. TITLE PAGE NO. 2.1 Emil Warburg Gabriel 8 5.1 Magneto-Caloric Effect 11 5.2 Process of Magneto-Caloric Effect 11 6.1 Flow Process Diagram A 12 6.2 Flow Process Diagram B 13 7.1 Comparison Between Magnetic Refrigeration & Conventional Refrigeration 14 7.2 Refrigeration Cycle For Conventional Gas Compression & Magnetic Refrigeration 15 8.1 Components 16 9.1 A Rotary AMR Liquefier 17
  • 5 ACKNOWLEDGEMENT I take this opportunity to express our deep sense of gratitude and respecttowards our guide MR. J. R. MAHAJAN, Department of Mechanical Engineering,Late G N Sapkal College Of Engineering , NASHIK. 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. T. Y. BADGUJAR 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 findplace in my report. I am also grateful to Senior Seminar Coordinators respected sir’s. HARDIK N KOTHIYA III year, VSem Deptt. Of Mechanical Engineering (L.G.N.S.COE, Nashik) Magnetic Refrigeration
  • 6 ABSTRACT The 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 caloric effect, which means that they increase and decrease in temperature whenmagnetized/demagnetized. This effect has been observed for many years and was used for cooling near absolute zero. Recently materials are being developed which have sufficient temperature and entropy change to make them useful for a wide range temperature applications. Magnetic refrigeration is an emerging technology that exploits the magneto- caloric effectfound in solid state refrigerants. The combination of solid-state refrigerants, water based heat transfer fluids and high efficiency leads to environmentally desirable products with minimal contribution to global warming. Among the numerous application of refrigeration technology air conditioning applications provide the largest aggregate cooling power and use of the greatest quantity of electric energy.
  • 7 1. INTRODUCTION Refrigeration 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 mechanical refrigeration a refrigerant is a substance capable of transferring heat that it absorbs at low temperatures and pressures to a condensing medium; inthe region of transfer, the refrigerant is at higher temperatures and pressures. By means of expansion, compression, and a cooling medium, such as air or water, the refrigerant removes heat from a substance and transfers it to the cooling medium. Our society is highly dependent on reliable cooling technology. Refrigeration iscritical toour health and the global economy. Consumer application includes air conditioning, food preservation, air dehumidification, beverage dispensing and ice making without refrigerant ion the food 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 a conventional refrigerator were considerably improved due to extended research and development efforts. Furthermore, some liquids used as refrigerants arehazardous chemicals, while other eventually escape into the environment contributingtowards ozone layer depletion and global warming and therefore, conventionalrefrigeration ultimately promotes deleterious trends in the global climate. Magnetic refrigerator, which has advantages in refrigeration efficiency, reliability, lownoise and environmental friendliness with respect to the conventional gas refrigerators, is becoming a promising technology to replace the conventional technique. The development of the magnetic material, magnetic refrigeration cycles, magnetic field and the refrigerator of room temperature magnetic refrigeration is introduced.
  • 8 2. HISTORY Fig. 2.1Emil WarburgGabriel The effect was discovered in pure iron in 1881 by E. Warburg. Originally, the cooling effect varied between 0.5 to 2 K/T. Major advances first appeared in the late 1920s when cooling via adiabatic demagnetization was independently proposed by two scientists: Debye (1926) and Giauque(1927). The process was demonstrated a few years later when Giauque and MacDougall in 1933used it to reach a temperature of 0.25 K. Between 1933 and 1997, a number of advances in utilization of the MCE for cooling occurred. This cooling technology was first demonstrated experimentally by chemist Nobel Laureate William F. Giauque and his colleague Dr. D.P. MacDougall in 1933 for cryogenic purposes (they reached 0.25 K) In 1997, the first near room temperature proof of concept magnetic refrigerator was demonstrated by Prof. Karl A. Gschneidner, Jr. by the Iowa State University at Ames Laboratory. This event attracted interest from scientists and companies worldwide that started developing new kinds of room temperature materials and magnetic refrigerator designs. Refrigerators based on the magneto caloric effect have been demonstrated in laboratories, usingmagnetic fields starting at 0.6 T up to 10 teslas. Magnetic fields above 2 T are difficult to produce with permanent magnets and are produced by a superconducting magnet (1 tesla is about 20,000 times the Earth's magnetic field).
  • 9 3.REFRIGERATION Refrigeration 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 lowering the temperature of the enclosed space or substance and then maintaining that lower temperature. The term cooing refers generally to any natural or artificial process by which heat is dissipated. The process of artificially producing extreme cold temperatures is referred to as cryogenics. Cold is the absence of heat, hence in order to decrease a temperature, one “removes heat", rather than "adding cold." In order to satisfy the Second Law of Thermodynamics, some form of work must be performed to accomplish this. This work is traditionally done by mechanical work but can also be done by magnetism, laser or other means. 3.1MAGNETIC REFRIGERATION Magnetic refrigeration, or adiabatic demagnetization, is a cooling technology based on themagneto caloric effect, an intrinsic property of magnetic solids. The refrigerant is often a paramagnetic salt, such as cerium magnesium nitrate. The active magnetic dipoles in this case are those of the electron shells of the paramagnetic atoms. A strong magnetic field is applied to the refrigerant, forcing its various magnetic dipolesto align and putting these degrees of freedom of the refrigerant into a state of lowered entropy. A heat sink then absorbs the heat released by the refrigerant due to its loss of entropy. Thermal contact with the heat sink is then broken so that the system is insulated, and the magnetic field is switched off. This increases the heat capacity of the refrigerant, thus decreasing its temperature below the temperature of the heat sink. Because few materials exhibit the needed properties at room temperature, applications have so far been limited to cryogenics and research.
  • 10 4. 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 hydrogen storage as it ignites on a very low temperature. Hydrogen Research Institute (HRI) is studying it with the help of magnetic refrigeration. We provide the cooling for the hydrogen storage by liquefying it. The hydrogen can be liquefied at a low temperature and the low temperature is achieved with the help of magnetic refrigeration.Thus, the magnetic refrigeration also provides a method to store hydrogen by liquefying it. The term used for such a device is magnetic liquefier. 5. MAGNETO CALORIC EFFECT The 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 by exposing the material to a changing magnetic field. This is also known as adiabaticdemagnetization by low temperature physicists, due to the application of the process specifically to affect a temperature drop. In that part of the overall refrigeration process, a decrease in the strength of an externally applied magnetic field allows the magnetic domains of a Chosen (magneto caloric) material to become disoriented from the magnetic field by the agitating Action of the thermal energy (phonons) present in the material. If the material is isolated so that no energy is allowed to (e) migrate into the material during this time (i.e. an adiabatic process), the temperature drops as the domains absorb the thermal energy to perform their reorientation. One of the most notable examples of the magneto caloric effect is in the chemicalelement gadolinium and some of its alloys. Gadolinium's temperature is observed to increase when it enters certain magnetic fields. When it leaves the magnetic
  • 11 field, the temperature returns to normal. The effect is considerably stronger for the gadolinium alloy Gd5 (Si2Ge2). Praseodymium alloyed with nickel (Pr Ni 5) has such a strong magneto caloric effect that it has allowed scientists to approach within one thousandth of a degree of absolute zero. Magnetic Refrigeration is also called as Adiabatic Magnetization. Fig. 5.1 Magneto-Caloric Effect Fig. 5.2 Process of Magneto-Caloric Effect
  • 12 1. WORKING OF MAGNETIC REFRIGERATION SYSTEM 6.1 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 temperature span of 38 K. The process flow diagram for the magnetic refrigeration system is shown in Fig. Fig.6.1 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. The fluid then passes through the copper plates attached to the no magnetized cooler-magneto caloric beds and loses heat. A fan blows air over this cold fluid into the freezer to keep the freezer temperature at approximately 0°F. The heat transfer fluid then gets heated up to 80°F, as it passes through the copper plates adjoined by the magnetized warmer magneto caloric beds, where it continues to cycle around the loop. However, the magneto caloric beds simultaneously move up and down, into and out of the magnetic field. The temperature of the refrigerator section is kept around 39°F. 6.2 Refrigerator Configuration :-
  • 13 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 at temperature of 0°F. Refrigerators maintain a temperature of 39°F. The refrigerator will be insulated with polyurethane foam, one of the most common forms of insulation available. The refrigerator is kept cool by forcing cold air from the freezer into the refrigerator by using a small fan. Fig. 6.2 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 the compressor off when the temperature gets below 0°F. A second thermostat regulates the fan that cools the refrigerator to 39°F. To maintain a frost-free environment in the freezer, a defrost timer will send power to a defrost heater on the coils for a fifteen minute time period every eight hours. In the first six minutes, the walls of the freezer will be defrosted. The water will then drain into a pan at the base of the refrigerator. The next nine minutes involve the safety factor of not reaching a temperature in the freezer that is too high. Also, a safety thermostat keeps the liquid water from freezing as it drains. The heat transfer fluid for the magnetic refrigeration system is a liquid alcohol watermixture. 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 operatingtemperatures. This heat transfer fluid is cheaper than traditional refrigerants and also eliminatesthe environmental damage produced from these refrigerants.
  • 14 7. COMPARISON BETWEEN MAGNETIC REFRIGERATION AND CONVENTIONAL REFRIGERATION Fig. 7.1Comparison between Magnetic Refrigeration and Conventional Refrigeration In 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 for a cooling process in two steps. The main Cooling usually occurs through the expansion of the gas. The steps of a magnetic refrigeration process are Analogous. By comparing a with b, inFigure.2 one can see That instead of compression of a gas, a magnetocaloric Material is moved into a magnetic field and that instead of Expansion it is moved out of the field. As explained in the Previous section, these processes change the temperature Of the material and heat may be extracted, respectively Injected just as in the conventional process. There are Some differencesbetween the two processes. The heat Injection and rejection in a gaseous refrigerant is a ratherFast process, because turbulent motion
  • 15 transports heat Very fast. Unfortunately, this is not the case in the solid Magneto-caloric materials. Here, the transport mechanism For heat is slow molecular diffusion. Therefore, at present fi Ligree porous structures are considered to be the best Solution to overcome this problem. The small distances From the central regions of the material to an adjacent fluid Domain, where a heat transport fluid captures the heat and Transports it out of the material, are ideal to make the Magnetic cooling process faster. Furthermore, the not very Large adiabatic temperature differences of magneto-caloric Materials will require more often a design of cascade or Regenerative magnetic refrigerators than in conventional Refrigerators and hence require additional heat transfer Steps. In the is the conventional gascompression Process is driven by continuously repeating The four different basic processes shown and is the Magnetic refrigeration cycle comparison. Compression is Replaced by adiabatic magnetization and expansion by Adiabatic demagnetization. Fig. 7.2 Refrigeration cycles for conventional gas compression and magnetic refrigeration 8. COMPONENTS
  • 16 Components required for construction :- Fig. 8.1Components 1. Magnets : - Magnets are the main functioning element of the magnetic refrigeration. Magnets providethe 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 thesurrounding. 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 themagnetic 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 inthe right desired direction. 5. Magneto caloric Wheel : - It forms the structure of the whole device. It joins both the two magnets to work properly. 9. APPLICATIONS
  • 17 9.1 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 a superconducting magnet. This technology can also be extended to the liquefaction of hydrogen. Fig. 9.1 A Rotary AMR liquefier 9.2 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 temperature spans occur between the heat source and the heat sink. Such are used for freezing, e.g. in cooling plants in the food industry or in large marine freezing applications. Some of the future applications are: 1. Magnetic household refrigeration appliances 2. Magnetic cooling and air conditioning in buildings and houses 3. Central cooling system 4. Refrigeration in medicine 5. Cooling in food industry and storage 6. Cooling in transportation 7. Cooling of electronics 10.TECHNICAL BENEFITS
  • 18 2. 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 Vapor Compression cycle. 3. Reduced operating cost: - As it eliminates the most inefficient part of today’s refrigerator i.e.comp. The cost reduces as a result. 4. 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 (say gadolinium) and not a gas as in case of vapor compression cycles. 5. Reliability: - Due to the absence of gas, it reduces concerns related to the emission into theatmosphere and hence is reliable one. 11. ADVANTAGES 1. Environmental friendly: - Conventional refrigerator use refrigerant that contains CFC or HCFC, which have been linked to Ozone depletion and global warming. Some refrigerant like ammonia are toxic and inflammable. 2. Low running and operating cost:-There is no compressor in magnetic refrigerator, which is most inefficient and costlier part. This leads in less energy consumption and hence low running cost. 3. Higher efficiency:-Because it eliminates the need to expand and compressed the liquid, magnetic refrigerator consume less energy and can operate at 60% efficiency. 4. Wide temperature span: - Operating temperature of magnetic refrigerator can easily be changed over a wide range from about 30 k to 290 k without losing the magneto-caloric effect.
  • 19 5. Reliability: - High energy density and more compact device, less moving parts as compared to traditional system hence more reliable. 6. Quite operation: - This refrigerator unit is substantially quite than traditional refrigeration system. 12. DISADVANTAGES On the other hand, some disadvantages include: 1. The initial investment is more as compared with conventional refrigeration. 2. The magneto caloric materials are rare earth materials hence their availability also addsup an disadvantage in MAGNETIC REFRIGERATION. GMCE materials need to be developed to allow higher frequencies of rectilinear androtary magnetic refrigerators. 3. Protection of electronic components from magnetic fields. But notice that they are static, of short range and may be shielded 4. Permanent magnets have limited field strength. Electromagnets and superconductingmagnets are (too) expensive. 5. Temperature changes are limited. Multi-stage machines lose efficiency through the heattransfer between the stages. 6. Moving machines need high precision to avoid magnetic field reduction due to gapsbetween the magnets and the magneto caloric material.
  • 20 13. CURRENT AND FUTURE USES There 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 of current research. A useful review on magneto caloric materials published in 2005 is entitled "Recent developments in magneto caloric materials" by Dr. Karl A. Gschneidner, .This effect is currently being explored to produce better refrigeration techniques, especially for use in spacecraft. This technique is already used to achieve cryogenic temperatures in the laboratory setting (below 10K). As an object displaying MCE is moved into a magnetic field, the magnetic spins align, lowering the entropy. Moving that object out of the field allows the object to increase its entropy by absorbing heat from the environment and disordering the spins. In this way, heat can be taken from one area to another. Should materials be found to display this effect near room temperature, refrigeration without the need for compression may be possible, increasing energy efficiency. In addition, magnetic refrigeration could also be used in domestic refrigerators. In 2006, 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 magnetic refrigeration. This has made the use of the expensive material gadolinium redundant, and made the creation of domestic magnetic refrigerators possible. The use of this technology for domestic refrigerators though is very remote due to the high efficiency of current Vapor-compression refrigeration in the range of 60% of Carnots efficiency. Gas molecules are responsible for heat transfer, they absorb heat in the inner side of the refrigerator by expanding and release this heat in the outside by condensing. The work provided to do this work is a cheap and highly efficient compressor, driven by an electric motor that is more than 80% efficient. This technology could eventually compete with other cryogenic heat pumps for gas liquefaction purposes.
  • 21 14. CONCLUSION If 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 the continual 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. At the end of this study we can say; 1. It is a technology that has proven to be environmentally safe. 2. In order to make the magnetic refrigerator commercially Viable, scientists need to know how to achieve larger temperature swings and also permanent magnets which canproduce strong magnetic fields of order 10 tesla. 3. There are still some thermal and magnetic hysteresis problems to be Solved for thematerials that exhibit the MCE to become really useful. 4. Magnetic materials available for room Temperature magnetic refrigeration are mainlyGd, Gdsige alloys, mnas-like materials, perovskitelike Materials, 5. Materials under development for room Temparature magnetic refrigeration are La(fexsi1-X)13 and La(Fe0.88Si0.12)13Hy 6. 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. 7. This technology must be universalized worldwide.
  • 22 15. REFERENCES 1. http://en.wikipedia.org/wiki/Magnetic_refrigeration 2. http://www.scribd.com/doc/19537314/Magnetic-Refrigeration 3. Lounasmaa, experimental principles and methods, academic press 4. Richardson and Smith, experimental techniques in condensed matter physics at low temperature, Addison Wesley (2003) 5. A text book on cryogenic engineering by V.J.Johnson 6. “Refrigeration and Air conditioning” by Arora and Domkundwar 7. Magnetic Refrigeration, ASHRAE Journal (2007), by John Dieckmann, Kurt Roth and James Brodrick