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MAGNETIC REFRIGERATION[.ppt (Size: 726 KB / Downloads: 24)
DEFINATION OF REFRIGERATION
“THE REFRIGERATION IS THE PROCESS OF REMOVING HEAT FROM A SUBSTANCE AND REJECTING THE HEAT SO REMOVED TO THE ATMOSPHERE WHICH IS AT A HIGHER TEMPRATURE LEVEL”
Magnetic refrigeration is a cooling technology based on the magneto caloric effect
A strong magnetic field is applied to the refrigerant
A heat sink then absorbs the heat released by the refrigerant
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.
Principle of Magnetic refrigeration :
Mageto calorific effect is the basic principle on which the cooling is achieved.
All magnets bears a property called Currie effect i.e. If a temperature of magnet is increased from lower to higher range at certain temperature magnet looses the magnetic field.
Currie temperature. Depends on individual property of each material
As Energy input to the magnet is increased the orientation of the magnetic dipoles in a magnet starts loosing orientation. And vice a versa at Currie temperature as magnet looses energy to the media it regains the property.
The increasing external magnetic field (+H) causes the magnetic dipoles of the atoms to align
The net result is that the item heats up (T + Tad)
Isomagnetic enthalpic transfer
This added heat can then be removed by a fluid like water or helium
The magnetic field is held constant to prevent the dipoles from reabsorbing the heat
The substance is returned to another adiabatic (insulated) condition so the total entropy remains constant
thermal energy causes the domains to overcome the field, and thus the sample cools
Magneto caloric effect is an intrinsic property of magnetic solid.
Ease of application and removal of magnetic effect is most desired propery of material. It is individual characteristics and strongly depends on :
Degree of freedom for magnetic dipoles during ordering and randomization of particals.
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