Magnetic Refrigiration

Magnetic Refrigiration

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  A Seminar Report On MAGNETIC REFRIGIRATION SubmittedIn partial fulfilment of The requirement for the award of the Degree Of BACHELOR OF TECHNOLOGY IN MECHANICAL ENGINEERING By: NADI BIDYADHARA College Roll.no-12ME021 DEPARTMENT OF MECHANICAL ENGINEERING GANDHI INSTITUTE OF ENGINEERING AND TECHNOLOGY GUNUPUR – 765022 2015-2016
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  ii Gandhi Institute of Engineering& Technology GUNUPUR – 765 022, Dist: Rayagada (Orissa), India (Approved by AICTE, Govt. of Orissa and Affiliated to BijuPatnaikUniversity of Technology) : 06857 – 250172(Office), 251156(Principal), 250232(Fax), e-mail: gandhi_giet@yahoo.com visit us at www.giet.org DEPARTMENT OF MECHANICAL ENGINEERING CERTIFICATE ISO 9001:2000 Certified Institute This is to certify that the seminar report work entitled “MAGNETIC REFRIGIRATION ”is the bonafide work carried out by NADI BIDYADHARA student of BACHELOR OF TECHNOLOGY, GANDHI INSTITUTE OF ENGINEERING AND TECHNOLOGY during the academic year 2015-16 in partial fulfilment of the requirements for the award of the Degree of BACHELOR OF TECHNOLOGY in MECHANICAL ENGINEERING. Prof. KALI CHARAN RATH Prof. A.V.N.L. SHARMA Semianr I/C HOD (MECH)
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  ACKNOWLEDGEMENT: Here I wouldlike to extent my heartfelt obligation to the following person for their sincere help and co-operation during the seminar presentation without whose help this report would never have been completed. Much credit and heartfelt thanks is owed to HOD (head of department) of my Institution GIET, GUNUPUR for encouraging and allowing me to present the topic “MAGNETIC REFRIGIRATION” at the seminar held at our department premises for the partial fulfilment of the requirements leading to the award of B-Tech degree. I also want to thank our department in charge Prof KALI CHARAN RATH. I am extremely grateful and indebted to them for her expert, sincere and valuable guidance and encouragement extended to me. Last but not the least I would like to extend a special word of thanks to all my friends and family members for giving me a helping hand whenever needed and for making the seminar a grand success. NADI BIDYADHARA MECH.
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  CONTENT Pages 1. Introduction1 2. The magnetocaloric effect 3 2.1 Equation 2.2 Applied technique 3. Thermodynamic cycle 7 4. Process of magnetic refrigiration 10 5. Woking materials 12 4.1 Parametric salt 4.2 Nuclear demagnetization 6. Commertial development 15 5.1 Current & Future uses 7. Historical background 16 8. Magnetothermodynamic machines 17 9. Advangages & disadvantages 19 10.Possible future applications 20 11. Conclusion 21
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  1.Introduction The refrigeration technologymarket is closely related to beverage and food production, industrial process, the chemical and pharmaceutical industry, the automotive sector, etc. Some of these sectors have strongly growing markets, thanks to the rising incomes of Eastern European, Indian and Chinese customers, with their desire for modern consumer goods driving such development. The retail market, supermarket and hypermarket chains are strongly benefiting from this development. Because the number of built alternative refrigeration technologies such as absorption or adsorption refrigeration, thermoelectric and thermoacoustic refrigeration, etc. is negligible, this leads to positive prospects for the gas-compression system producers. Furthermore, the tendency to cool domestic buildings in southern areas is also increasing. The business-as-usual scenario, based on dynamic numerical climatological system simulations, was published by the European Commission. The prediction for the year 2010 is an HFC emission level the equivalent of 66 Mtonnes CO2. This is an
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  increase of 62%based on the value of 1995. Refrigeration and air [1] conditioning are responsible for the main fraction, namely 43%. What are the alternatives, if HFCs also will have to be reduced? This is a desire of an increasing number of politicians that already has been announced in some countries. Maybe new less harmful refrigerants will be discovered. A new blend H has just been developed and announced by an industrial company, but up until now, reliable experience is missing. The time would be ideal for an alternative refrigeration technology such as, for example, magnetic refrigeration. For the interested reader, who wants to gain a greater insight into magnetic heat pumps and refrigerators than given in this short informatory note, several review articles are available . This promising technology works without a gaseous refrigerant and its energy efficiency (coefficient of performance, COP) in principle can be higher than that of a conventional refrigeration system. As a result, its breakthrough in certain domains of the refrigeration market would lead to less CO2 output into the atmosphere. This informatory note gives an overview of this spectacular technology, discusses ideal and not-so-promising applications and reports on some problems which have to be solved in order to enter industrialising phases for the various refrigeration applications envisaged.
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  [2] (Fig-1 .Gadolinium alloyheats up inside the magnetic field and loses thermal energy to the environment, so it exits the field cooler than when it entere.) . 2.The magnetocaloric effect The magnetocaloric effect (MCE, from magnet and calorie) is a magneto-thermodynami phenomenon in which a temperature change of a suitable material is caused by exposing the material to a changing magnetic field. This is also known by low temperature physicists as adiabatic demagnetization. In that part of the refrigeration process, a decrease in the strength of an externally applied magnetic field allows
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  the magnetic domainsof a magnetocaloric 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 (re)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 [3] at the curie temperature of a ferromagnetic material, except that magnetic dipoles overcome a decreasing external magnetic field while energy remains constant, instead of magnetic domains being disrupted from internal ferromagnetism as energy is added. One of the most notable examples of the magnetocaloric effect is in the chemical element gadolinium and some of its alloys. Gadolinium's temperature increases when it enters certain magnetic fields. When it leaves the magnetic field, the temperature drops. The effect is considerably stronger for the gadolinium alloy , Praseodymiumalloyed with nickel has such a strong magnetocaloric effect that it has allowed scientists to approach to within one milliKelvin, one thousandth of a degree of absolute zero.
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  Equation The magnetocaloric effectcan be quantified with the equation below: [4] where T is the temperature, H is the applied magnetic field, C is the heat capacity of the working magnet (refrigerant) and M is the magnetization of the refrigerant.
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  From the equationwe can see that magnetocaloric effect can be enhanced by: • applying a large field • using a magnet with a small heat capacity • using a magnet with a large change in magnetization vs. temperature, at a constant magnetic field. Applied Technique The basic operating principle of an adiabatic demagnetization refrigerator (ADR) is the use of a strong magnetic field to control the entropy of a sample of material, often called the "refrigerant". Magnetic field constrains the orientation of magnetic dipoles in the refrigerant. The stronger the magnetic field, the more aligned the dipoles are, corresponding to lower entropy and heat capacity because the material has (effectively) lost some of its internal degrees of freedom. If the refrigerant is kept at a constant temperature through thermal contact with a heat sink (usually liquid helium) while the magnetic field is switched on, the refrigerant must [5] lose some energy because it is equilibrated with the heat sink. When the magnetic field is subsequently switched off, the heat capacity of the refrigerant rises again because the degrees of freedom associated with orientation of the dipoles are once again liberated, pulling their share of equipartitioned energy from the motion of the molecules, thereby lowering the overall temperature of a system with decreased energy. Since the system is now insulated when the magnetic field is switched off, the process is adiabatic, i.e., the system can no longer exchange energy with its surroundings (the heat sink), and its temperature decreases below its initial value, that of the heat sink.
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  The operation ofa standard ADR proceeds roughly as follows. First, a strong magnetic field is applied to the refrigerant, forcing its various magnetic dipoles to align and putting these degrees of freedom of the refrigerant into a state of lowered entropy. The 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, increasing the heat capacity of the refrigerant, thus decreasing its temperature below the temperature of the heat sink. In practice, the magnetic field is decreased slowly in order to [6] provide continuous cooling and keep the sample at an approximately constant low temperature. Once the field falls to zero or to some low limiting value determined by the properties of the refrigerant, the cooling power of the ADR vanishes, and heat leaks will cause the refrigerant to warm up. 3.Thermodynamic cycle
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  (Fig-2thermodynamic cycle) The cycleis performed as a refrigeration cycle that is analogous to the Carnot refrigeration cycle, but with increases and decreases in magnetic field strength instead of increases and decreases in pressure. It can be described at a starting point whereby the chosen working substance is [7] 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.
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  • 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 substance is heated (T + ΔTad). • 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). [8] • 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
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  causes the magneticmoments 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 reheating. The material is placed in thermal contact with the environment to be refrigerated. Because the working material is cooler than the refrigerated environment (by design), heat energy migrates into the working material (+Q). Once the refrigerant and refrigerated environment are in thermal equilibrium, the cycle can restart. [9] 4.Processes of magnetic refrigeration
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  Figure 3 –the conventional gas-compression process is driven by continuously repeating the four different basic processes shown in this figure.) (Figure 4 – the magnetic refrigeration cycle comparison. Compression is replaced by adiabatic magnetisation and expansion by adiabatic demagnetisation.) In Figure 3 the four basic steps of a conventional gascompression/expansion refrigeration process are shown. These [10] 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
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  main cooling usuallyoccurs through the expansion of the gas. The steps of a magnetic refrigeration process are analogous. By comparing Figure 3 with Figure 4, one can see that instead of compression of a gas, a magnetocaloric material is moved into a magnetic field and that instead of expansion it is moved out of the field. As explained in the previous section, these processes change the temperature of the material and heat may be extracted, respectively injected just as in the conventional process. There are some differences between the two processes. The heat injection and rejection in a gaseous refrigerant is a rather fast process, because turbulent motion transports heat very fast. Unfortunately, this is not the case in the solid magnetocaloric materials. Here, the transport mechanism for heat is slow molecular diffusion. Therefore, at present filigree porous structures are considered to be the best solution to overcome this problem. The small distances from the central regions of the material to an adjacent fluid domain, where a heat transport fluid captures the heat and transports it out of the material, are ideal to make the magnetic cooling process faster.Furthermore, the not very large adiabatic temperature differences of magnetocaloric materials will require more often a design of cascade or regenerative magnetic refrigerators than in conventional refrigerators and hence require additional heat transfer steps. [11] 5.Working material The magnetocaloric effect (MCE) is an intrinsic property of a magnetic solid. This thermal response of a solid to the application or
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  removal of magneticfields is maximized when the solid is near its magnetic ordering temperature. Thus, the materials considered for magnetic refrigeration devices should be magnetic materials with a magnetic phase transition temperature near the temperature region of interest. For refrigerators that could be used in the home, this temperature is room temperature. The temperature change can be further increased when the order-parameter of the phase transition changes strongly within the temperature range of interest. The magnitudes of the magnetic entropy and the adiabatic temperature changes are strongly dependent upon the magnetic ordering process. The magnitude is generally small in antiferromagnets, ferrimagnets and spin glass systems but can be much larger for ferromagnets that undergo a magnetic phase transition. First order phase transitions are characterized by a discontinuity in the magnetization changes with temperature, resulting in a latent heat. Second order phase transitions do not have this latent heat associated with the phase transition. In the late 1990s Pecharksy and Gschneidner reported a magnetic entropy change in Gd5si2Ge2 that was about 50% larger than that reported for Gd metal, which had the largest known magnetic entropy change at the time. This giant magnetocaloric effect (GMCE) occurred at 270K, which is lower than that of Gd (294K). Since the MCE occurs below room temperature these materials would not be suitable for refrigerators operating at room temperature. [12] Since then other alloys have also demonstrated the giant magnetocaloric effec. These are include Gd 5(SixGe1−x)4, La(FexSi1−x)13Hx and MnFeP1−,x alloys,. Gadolinium
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  and its alloysundergo second-order phase transitions that have no magnetic or thermal hysteresis. However, the use of rare earth elements makes these materials very expensive. Ni 2Mn-X (X = Ga, Co, In, Al, Sb) Heusler alloys are also promising candidates for magnetic cooling applications because they have Curie temperatures near room temperature and, depending on composition, can have martensitic phase transformations near room temperature. These materials exhibit the magnetic shape memory effect and can also be used as actuators, energy harvesting devices, and sensors. When the martensitic transformation temperature and the Curie temperature are the same (based on composition) the magnitude of the magnetic entropy change is the largest. In February 2014, GE announced the development of a functional Ni-Mn-based magnetic refrigerator. The development of this technology is very material-dependent and will likely not replace vapor-compression refrigeration without significantly improved materials that are cheap, abundant, and exhibit much larger magnetocaloric effects over a larger range of temperatures. Such materials need to show significant temperature changes under a field of two tesla or less, so that permanent magnets can be used for the production of the magnetic field. Paramegnetic salts: The original proposed refrigerant was 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 .In a [13] paramagnetic salt ADR, the heat sink is usually provided by a pumped .He(about1.2 K)or He (about0.3 K) cryostat. An easily attainable 1 T magnetic field is generally required for initial magnetization. The minimum temperature attainable is determined by
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  the self-magnetization tendenciesof the refrigerant salt, but temperatures from 1 to 100 mK are accessible. Dilution refrigerators had for many years supplanted paramagnetic salt ADRs, but interest in space-based and simple to use lab-ADRs has remained, due to the complexity and unreliability of the dilution refrigerator Eventually paramagnetic salts become either diamagnetic or ferromagnetic, limiting the lowest temperature that can be reached using this method. Nuclear demagnetization: One variant of adiabatic demagnetization that continues to find substantial research application is nuclear demagnetization refrigeration (NDR). NDR follows the same principles, but in this case the cooling power arises from the magnetic dipoles of the nuclei of the refrigerant atoms, rather than their electron configurations. Since these dipoles are of much smaller magnitude, they are less prone to self-alignment and have lower intrinsic minimum fields. This allows NDR to cool the nuclear spin system to very low temperatures, often 1 µK or below. Unfortunately, the small magnitudes of nuclear magnetic dipoles also makes them less inclined to align to external fields. Magnetic fields of 3 teslas or greater are often needed for the initial magnetization step of NDR. In NDR systems, the initial heat sink must sit at very low temperatures (10–100 mK). This precooling is often provided by the mixing chamber of a dilution refrigerator or a paramagnetic salt. [14] 6.Commercial development
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  Research and ademonstration proof of concept in 2001 succeeded in applying commercial-grade materials and permanent magnets at room temperatures to construct a magnetocaloric refrigerator. On August 20, 2007, the Risø National Laboratory (Denmark) at the Technical University of Denmark, claimed to have reached a milestone in their magnetic cooling research when they reported a temperature span of 8.7 K. They hope to introduce the first commercial applications of the technology by 2010. As of 2013 this technology had proven commercially viable only for ultra-low temperature cryogenic applications available for decades. Magnetocaloric refrigeration systems are composed of pumps, motors, secondary fluids, heat exchangers of different types, magnets and magnetic materials. These processes are greatly affected by irreversibilities and should be adequately considered. At year-end, Cooltech Applications announced that its first commercial refrigeration equipment would enter the market in 2014. At the 2015 Consumer Electronics Show in Las Vegas, a consortium of Haier,Astronautics Corporation of America andBASF presented the first cooling appliance. BASF claim of their technology a 35% improvement over using compressors. [15] Current & future uses:
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  Thermal and magnetichysteresis problems remain to be solved for first-order phase transition materials that exhibit the GMCE. One potential application is in spacecraft. Vapor-compression refrigeration units typically achieve performance coefficients of 60% of that of a theoretical ideal Carnot cycle, much higher than current MR technology. Small domestic refrigerators are however much less efficient. In 2014 giant anisotropic behaviour of the magnetocaloric effect wasfound in (Ho(Mn)2O5 ) at 10 K. The anisotropy of the magnetic entropy change gives rise to a large rotating MCE offering the possibility to build simplified, compact, and efficient magnetic cooling systems by rotating it in a constant magnetic field. 7.Hystorical background The effect was discovered using nickel in 1917 by French physicist Pierre Weiss and Auguste Piccard. Originally, the cooling effect was less than 0.5 K/T. Major advances first appeared in the late 1920s when cooling via adiabatic demagnetization was independently proposed by Peter Debye in 1926 and chemistry Nobel LaureateWilliam F. Giauque in 1927. It was first demonstrated experimentally by Giauque and his colleague D. P. MacDougall in 1933 for cryogenic purposes when they reached 0.25 K. Between 1933 and 1997, advances in MCE cooling occurred. [16]
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  In 1997, thefirst near room-temperature proof of concept magnetic refrigerator was demonstrated by Karl A. Gschneidner, Jr. by the Iowa State University at Ames Laboratory. This event attracted interest from scientists and companies worldwide who started developing new kinds of room temperature materials and magnetic refrigerator designs. A major breakthrough came 2002 when a group at the University of Amsterdam demonstrated the giant magnetocaloric effect in MnFe(P,As) alloys that are based on abundant materials. Refrigerators based on the magnetocaloric effect have been demonstrated in laboratories, using magnetic fields starting at 0.6 T up to 10 T. Magnetic fields above 2 T are difficult to produce with permanent magnets and are produced by a superconducting magnet (1 T is about 20,000 times the Earth's magnetic field). 8.Megnetothermodynamic machines Application of the GMCE calls for a magnetic field change in a magnetocaloric material. This can be performed using different magnetic refrigeration principles: • alternatively changing magnetic fields in static blocks of magnetocaloric material by application of electromagnets • rectilinear motion of magnetocaloric material with static permanent magnet assemblies • rectilinear motion of permanent magnet assemblies with static magnetocaloric material blocks. [17] • rotary motion of magnetocaloric material with static permanent magnet assemblies
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  • rotary motionof permanent magnet assemblies with static magnetocaloric material blocks. The basic magnetothermodynamic cycles are the Carnot cycle, the Brayton cycle and the Ericsson cycle. A review of the magnetothermodynamics of magnetic refrigeration is given in Reference 8. Also, cascade and regeneration processes are explained. Another concept is the application of the active magnetic refrigeration principal (AMR) [18] Until now, studies on 28 prototypes have been published and some of their characteristics were listed (for a partial overview, see Reference 10). One of the most successful machines was built by Astronautics Corporation, USA.
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  This rotary typeof magnetic refrigerator is operated with a frequency of up to 4 Hz. It has a magnetic field induction of 1.5 T, is filled with gadolinium spheres and has a cooling capacity of 95 W with a maximum temperature span of 20 K prototypes have been built by the Material Science Institute in Barcelona, Spain; Chubu Electric/Toshiba, Yokohama, Japan; a group at the University of Victoria, British Columbia, Canada; Sichuan Institute of Technology/Nanjing University, Nanjing, China; the Laboratoire d’Electronique Grenoble in Grenoble and Cooltech Applications, France . The prototype designed by the University of Victoria applies the layered bed technique with two different materials. By choosing different alloys at different positions in the refrigerator, the performance of the refrigerator is increased. 9.Advantages & disadvantages The potential advantages of magnetic refrigeration are valid in comparison with the direct evaporation refrigerating machines: • “Green” technology, no use of conventional refrigerants. • Noiseless 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. [19] • Simple design of machines, e.g. rotary porous heat exchanger refrigerator. • Low maintenance costs.
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  • Low (atmospheric)pressure. This is an advantage in certain applications such as in air-conditioning and refrigeration units in automobiles. On the other hand, some disadvantages include: • 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. Electro magnets and superconducting magnets are (too) expensive. • Temperature changes are limited. Multi-stage machines lose efficiency 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 magnetocaloric material. 10.Possible future application The list of possible applications involves all domains of refrigeration, heat pump technology and power conversion. But there are two conditions which limit the applications of the technology in its current state. The first is the temperature span. If the difference between the upper and lower temperature levels is large, then the number of stages becomes also large and a practical realisation is no longer economic. [20]
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  The second conditionis the stability of the running conditions. Because the MCE is limited to a domain around the Curie temperature where the continuous phase transition occurs, it is difficult to operate magnetic refrigerating machines under highly fluctuating conditions. More or less stable temperature levels are required for a reliable and efficient operation of a magnetic refrigeration system. The potential for cost-effective magnetocaloric air-conditioning systems was outlined by Russek and Zimm in the Bulletin of the IIR. 11.Conclusion Magnetic refrigeration is undoubtedly a promising technology that should be encouraged because of its numerous advantages, in particular energy saving and environmental
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  [21]