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Seminar on Magnetic Refrigeration Report Download
The objective of this effort is to study the Magnetic Refrigeration which uses solid materials as the refrigerant. These materials demonstrate the unique property known as magneto caloric effect, which means that they increase and decrease in temperature when magnetized /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 magnetocaloric effect found 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.
Refrigeration is the process of removing heat from matter which may be a solid, a liquid, or a gas. Removing heat from 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; in the 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 is critical to our health and the global economy. Consumer application includes air conditioning, food preservation, air dehumidification, beverage dispensing and ice making without refrigeration the
food supply wood still be seasonal and limited to locally produced non-perishable items.
Modern refrigeration is almost entirely based on a compression/ expansion refrigeration cycle. 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 are hazardous chemicals, while other eventually escape into the environment contributing towards ozone layer depletion and global warming and therefore, conventional refrigeration ultimately promotes deleterious trends in the global climate.
OBJECTIVES OF MAGNETIC REFRIGERATION
To develop more efficient and cost effective small scale H2 liquefiers as an alternative to vapor-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.
As shown in the figure, when the magnetic material is placed in the magnetic field, the thermometer attached to it shows a high temperature as the temperature of it increases. But on the other side when the magnetic material is removed from the magnetic field, the thermometer shows low temperature as its temperature decreases The place we want to cool it, we will apply magnetic field to the material in that place and as its temperature increases, it will absorb heat from that place and by taking the magnetic material outside in the surroundings, we will remove the magnetic material from magnetic field and thus it will lose heat as its temperature decreases and hence the cycle repeats over and again to provide the cooling effect at the desired place.
Magnetic Refrigeration system : –
Consists of two beds containing spherical powder of Gadolinium with water being used as 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
A mixture of water and ethanol serves as the heat transfer fluid for the system. 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 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 second position of the beds is shown in Figure 6.4. The cold air from the freezer is blown into the refrigerator by the freezer fan shown in Figure 6.5. The temperature of the refrigerator section is kept around 39°F.
Components required for construction :-
2. Hot Heat exchanger
3. Cold Heat Exchanger
5. Magneto caloric wheel
1. Magnets : –
Magnets are the main functioning element of the magnetic refrigeration. Magnets provide the 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 the surrounding. 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 the magnetic 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 in the right desired direction.
5. Magneto caloric Wheel : –
It forms the structure of the whole device. It joins both the two magnets to work properly.
Advantages : –
- The potential advantages of magnetic refrigeration bare valid in comparison with the direct evaporation refrigerating machines:
- Purchase cost may be high, but running costs are 20% less than the conventional chillers.
- Thus life cycle cost is much less.
- Ozone depleting refrigerants are avoided in this system, hence it more eco-friendly.
- Energy conservation and reducing the energy costs are added advantages.
- The efficiency of magnetic refrigeration is 60% to 70% as compared to Carnot cycle.
- Magnetic refrigeration is totally maintenance free & mechanically simple in construction.
- “green” technology, no use of conventional refrigerants
- Noise less 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
- Simple design of machines, e.g. Rotary porous heat exchanger refrigerator
- 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:
- 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.
- 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. Electromagnets and superconducting magnets are (too) expensive
- Temperature changes are limited. Multi-stage machines lose effi ciency 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 magneto caloric material.
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