MAGNETIC REFRIGERATION (1)

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MAGNETIC REFRIGERATION BRAND NEW TREND IN FIELD OF REFRIGERATION:

MAGNETIC REFRIGERATION BRAND NEW TREND IN FIELD OF REFRIGERATION PRESENTED BY P.BHARATH VAISHNAVI INSTITUTE OF TECHNOLOGY

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This is new generation cooling technology working on the basis of magneto caloric effect which is intrinsic property of magnetic solids. The refrigerant is often a paramagnetic salt, such as cerium magnesium nitrate. The magnetic refrigeration could be used in any possible application where cooling, heating or power generation is used today. It gives cooling nearer to absolute zero than any other method hence it makes liquification of gases easier. At the same time it does not emit any CFC or HCFC compounds hence it never effects our environment specially OZONE layer. INTRODUCTION

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A magneto-thermodynamic phenomenon in which a reversible change in temperature of a suitable material is caused by exposing the material to a changing magnetic field. The decrease in the strength of an externally applied magnetic field disorientes the magnetic domains of a chosen magneto caloric material from the magnetic field, the energy required for disorientation is absorbed in form of heat from substance to be cooled. When strength of externally applied magnetic field starts increasing magnetic domains start orientation with magnetic field hence reject the heat absorbed from substance to be cooled to a coolent. Magneto caloric effect

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Magnetic refrigeration cycle

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Magnetic refrigeration cycle As shown above there is analogy between MAGNETO CALORIC CYCLE & VAPOUR REFRIGERATION CYCLE H = externally applied magnetic field & Q = heat quantity The steps involving in magnetic refrigeration cycle can be given as follows. Magnetization: The 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). Isomagnetic enthalpic transfer: This added heat can then be removed by a fluid like water or helium for example (-Q). The magnetic field is held constant to prevent the dipoles from reabsorbing the heat. Once sufficiently cooled, the magneto caloric material and the coolant are separated (H=0). Demagnetization: The substance is returned to another adiabatic condition so the total entropy remains constant. However, this time the magnetic field is decreased, the thermal energy causes the domains to overcome the field, and thus the sample cools (i.e. an adiabatic temperature change). Energy transfers from thermal entropy to magnetic entropy i.e. 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, heat energy migrates into the working material (+Q).Once the refrigerant and refrigerated environment is in thermal equilibrium, the cycle continues.

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Entropy(S) –Temp. (T) Diagram

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Working materials

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Working materials MCE is an intrinsic property of a magnetic solid. It is maximized when the solid is near its magnetic ordering temperature. Gadolinium and its alloys are the best material available today for magnetic refrigeration near room temperature since they undergo second-order phase transitions which have no magnetic or thermal hysteresis involved. Alloys of gadolinium produce 3 to 4 K per tesla of change in a magnetic field hence can be used for magnetic refrigeration or power generation purposes. Eventually paramagnetic salts become either diamagnetic or ferromagnetic, limiting the lowest temperature which can be reached using this method.

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Magnetic refrigerator design

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advantages Magnetic refrigeration is environment friendly because there is no production of CFC, hazardous chemicals like NH3 (Ammonia) and greenhouse gases also does not affect OZONE layer. The efficiency of magnetic refrigeration is 60% to 70% as compared to Carnot cycle. The magnetic refrigeration consumes less power. Magnetic refrigeration is totally maintenance free & mechanically simple in construction. The C.O.P. (coefficient of performance) is very good as compared with conventional refrigeration.

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As every coin has 2 sides, this technique also posses some drawbacks to be worked on The initial investment is more as compared with conventional refrigeration. The magneto caloric materials are rare earth materials hence their availability also adds up an disadvantage in MAGNETIC REFRIGERATION. disadvantages

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Magnetic refrigeration is currently being used to produce better refrigeration techniques, especially in spacecraft. Magnetic refrigeration is used as to produce very low temperature as 1 Kelvin. As the through magnetic refrigeration we can produce 20 Kelvin temperature which is liquefied point of Hydrogen gas so we can get liquid hydrogen gas from air as a fuel. Magnetic refrigeration is used in food preservation applications. Magnetic refrigeration is used to produce small as well as large capacity of crayocoolers. This crayocoolers have a lot many applications in Cryogenics. applications

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Liquid hydrogen could prove to be a perfect fuel, but there are few technological hurdles. One of the biggest hurdles, an efficient method of liquefying hydrogen which is eliminated by MAGNETIC REFRIGERATION CASE STUDY – LIQUIFIED HYDROGEN Scientists have developed a highly efficient magneto caloric material that makes magnetic refrigeration technology efficient enough to cheaply produce liquid hydrogen . Latest discovery of new class of alloys with significantly more cooling power than the best existing materials opened a new door towards development. The new material gadolinium has two to three times the magneto caloric effect than a typical ferromagnetic iron and a popular choice for low-temperature ranges. Gd5Si2Ge2 is one of a family of compounds that exhibits a giant magneto caloric effect and whose ordering temperature can be tuned from 30 Kelvin (-405.4 F) to near room temperature (290 K or 62.6 F) by adjusting the ratio of silicon to germanium. After building the magnetic refrigerator and successfully liquefying hydrogen, It was found that the condensation efficiency accomplished 90% Carnot and the liquefaction power was 25.3 W in hydrogen liquefaction process at atmospheric pressure. Study of refrigerator performance & in addition, development of a hydrogen level detector to directly measure the amount of the liquid is going on.

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conclusion Magnetic refrigeration has greater efficiency and would have beneficial effects on national power consumption. However, continued research in material sciences will be required to find a low cost material solution to magnetic refrigerant. In addition, because permanent magnets account for a significant portion of the cost of prototypical systems, the development of higher performance and lower cost permanent magnet materials in the magnet industry will benefit the economics of magnetic refrigeration.

ANY QUESTION ???:

ANY QUESTION ??? Thank you