29-06-2012, 05:20 PM
MAGNETIC & NUCLEAR COOLING
MAGNETIC & NUCLEAR COOLING.ppt (Size: 722.5 KB / Downloads: 107)
Introduction : Principle
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 magetic dipoles in a maget starts loosing orientation. And vice a versa at currie temperature as maget looses energy to the media it regains the property.
Adiabatic magnetization
Procedure to be followed :
> Substance placed in insulated environment.
> Magnetic field +H increased.
> Magnetic dipoles of atoms to align, thereby
material decreases.
> Total Entropy of the item is not reduced, and item heats up
Isomagnetic entropic transfer
> Material is placed in thermal contact with the environment being refrigerated.
> Magnetic field held constant to prevent from heating back up
> Because the working material is cooler than the refrigerated environment, heat energy migrates into the working material ( +Q )
Once the refrigerant and refrigerated environment are in thermal equillibrium, the cycle begins a new
Working Materials
> Magneto caloric effect is an intrinsic porperty 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 :
Curie temperature,
Degree of freedom for magnetic dipoles during ordering and randomization of particals.
> ferrimagnets, antiferromagnets and spin glass sytems are not suitable for this application
Alloys of gadolinium producing 3 to 4 K per tesla of change in magnetic field are used for magnetic refrigeration or power generation purposes.