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MAGN A NATIONAL LEVEL PRESENTATION AT C.O.E.T , BAMBHORIETICREFRIGERATI BYON AJINKYA PATIL
1. INTRODUCTION2. MAGNETOCALORIC EFFECT3. MAGNETIC REFRIGERATION4. MAGNETIC REFRIGERATION CYCLE5. ADVANTAGES AND DRAWBACKS6. MAGNETIC MATERIALS FOR MAGNETIC REFREGERATION7. MAGNETIC REFRIGERATORS8. CONCLUSION
i. Refrigeration is the process of removing heat from matter which may be a solid, a liquid, or a gas.ii. Removing heat from the matter cools it, or lowers its temperature.iii. In a simple refrigerator ,the refrigerant removes heat from a substance and transfers it to the cooling medium .iv. There exist serious concerns for the environment .v. it is necessary and important to explore other alternative cooling technologies .vi. magnetic refrigerator, which has advantages in refrigeration efficiency, reliability, low noise and environmental friendliness
Warburg first discovered the thermal effect of metal iron in a varying magnetic field in 1881 . In recent years, MCE has been greatly developed in the room temperature range . reversible temperature change in some materials exhibit when exposed to a changing magnetic field . In these materials, a significant change in entropy can be effected by the application or removal of a magnetic field ..
The total entropy can be written as a function of temperature, T, MCE increases with field strength, superconducting magnets were used almost exclusively in MR devices Figure 1. Magnetocaloric effect with gadolinium .
When a magneto caloric material is subjected to a strong magnetic field, electron spins within the material . When the magnetic field is lowered, the electron spins return to their more random, higher energy state, absorbing heat from the material and causing the temperature to fall. The magnetic field does work to align the electron spins into what is, thermodynamically, a more highly ordered, lower energy state.
Magnetic refrigeration Magnetic refrigeration is based on a fundamental thermodynamic property of magnetic materials magneto caloric effect, which causes a temperature change if the material is subject to an applied magnetic field under adiabatic conditions Magnetic refrigeration has been recognized as being an alternative technology to the conventional vapour compression technology it is an environmentally friendly cooling techniques avoiding ozone-depleting or global-warming gases. Essentially material with the large MCE and high magnetic field created by magnetic field source it does not use chlorofluorocarbons that can negatively influence ozone layer depletion
four basic steps of a conventional gas compression expansion refrigeration process are shown .These are a compression of a gas, extraction of heat, expansion of the gas, and injection of heat . Figure 2. Refrigeration cycles for conventional gas compression and magnetic refrigeration
The main cooling usually occurs through the expansion of the gas . instead of compression of a gas, a magneto caloric material is moved into a magnetic field and that instead of expansion it is moved out of the field. These are some differences between the two processes. Compression is replaced by adiabatic magnetization and expansion by adiabatic demagnetization. The heat injection and rejection in a gaseous refrigerant is a rather fast process
“green” technology, no use of conventional refrigerants noiseless technology higher energy efficiency simple design of machines, low maintenance costs protection of electronic components from magnetic fields. permanent magnets have limited field strength.
At first, some ferromagnets were investigated for the large MCE existing in them . the giant MCE was found in GdSiGe alloys . materials for application in magnetic refrigerators:• binary and ternary inter metallic compounds• gadolinium-silicon-germanium compounds• magnates• lanthanum-iron based compounds• manganese-antimony arsenide• iron-manganese-arsenic phosphides
magnetic refrigeration could be competitive with conventional refrigerators operating below ambient temperatures The energy savings by replacing a conventional gas-cycle estimated to be 30% . with a custom designed permanent magnet it can produce a magnetic field strength nearly twice as high as the general permanent magnet field
Strong magnetic field is required. Large MCE of magnetic material is investigated for room temperature magnetic cooling application Excellent behaviour of regeneration and heat transfer is required Room temperature magnetic refrigeration is a new highly efficient It can be use household refrigerator, central cooling systems, room air conditioners and supermarket refrigeration applications. It is environmentally protective technology This technology must be universalized worldwide