Magnetic refrigerator

IntroductionMagnetic refrigeration is a cooling technology

based on the magnetocaloric effect. This technique can be used to attain extremely

low temperatures (well below 1kelvin), as well as the ranges used in common refrigerators, depending on the design of the system.

Magnetic refrigeration has been recognized as being an alternative technology to the conventional vapor compression technology.

HistoryThe effect was discovered in pure iron in 1881

by German physicist Emil. Warburg.Major advances first appeared in the late 1920s

when cooling via adiabatic demagnetization was independently proposed by two scientists: Debye (1926) and Giauque (1927).

The process was demonstrated a few years later when Giauque and MacDougall in 1933 used it to reach a temperature of 0.25 K.

Between 1933 and 1997, a number of advances in utilization of the MCE for cooling occurred.

History (contd.)In 1976, Brown presented first room

temperature refrigerator by applying Magneto Caloric Effect.

After the discovery of the giant magnetocaloric effect (GMCE) Gd5(Si2Ge2) in 1997 by Gashneidner and Pecharsky, which increases the MCE, many researchers concede that it has good future potential.

Magneto Caloric Effect

The Magneto caloric effect is 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.

In these materials significant change in entropy can be affected by the application or removal of the magnetic field.

Magnetic Refrigeration CycleThe steps of a magnetic refrigeration process are

analogous vapour compression refrigeration cycle.

one can see from the figure shown that instead of compression of a gas, a magnetocaloric material is moved into a magnetic field and that instead of expansion it is moved out of the field.

The main difference in both cycles is that the heat injection and rejection in a gaseous refrigerant is a rather fast process, because turbulent motion transports heat very fast. But this is not the case in the solid magnetocaloric materials.

Working of Magnetic Refrigerator

Working Steps1. Adiabatic magnetization

2. Isomagnetic enthalpic transfer

3. Adiabatic demagnetization

4. Isomagnetic entropic transfer

Adiabatic MagnetizationThe substance is placed in an insulated environment. The increasing external magnetic field causes the magnetic dipoles of the atoms

to align, thereby decreasing the material's

magnetic entropy and heat capacity. Due to this temperature of magnetocaloric material

increases is increased

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 fromreabsorbing the heat. Once sufficiently cooled, the magnetocaloric material and the coolant are separated.

Adiabatic DemagnetizationThe 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. Energy transfers from thermal entropy to

magnetic entropy (disorder of the magnetic dipoles).

Isomagnetic Entropic TransferThe 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 (by design), heat energy migrates into the working material.

Types of Magnetic Refrigerator

Reciproctory TypeRotatory Type

Components of Magnetic Refrigerator

MagnetsHot Heat exchangerCold Heat ExchangerDriveMagneto caloric material

MagnetsMagnets are the main functioning elementOf the magnetic refrigeration. Magnets provide the magnetic field to the material so that they can loose or gain the heat to the surrounding and from the space to becooled respectively.

Hot Heat Exchanger

The hot heat exchanger absorbs the heat from the material used and gives off to thesurrounding. It makes the transfer of heat much effective.

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.

Drive

Drive provides the right motion to the magnets or magneto caloric material so that change in magnetic field occurs.

Magneto caloric Material

It forms the structure of the whole device. Its design is made in such a way that maximum heat transfer occurs.

BENEFITSTECHNICALHigher EfficiencyReduced CostCompactnessSimple Design

BENEFITS (Contd.)SOCIO-ECONOMICGreen technology Competition in global marketLow capital costKey factor to new technologiesNoiseless technology

DrawbacksGMCE materials need to be developed.Protection of electronic components from

magnetic fields.Permanent magnets have limited field

strength.Moving machines need high precision.

ConclusionMagnetic refrigeration is undoubtedly a promising technology that should be encouraged because of its numerous advantages, in particular energy saving and environmental benefits