Project Guide:Prof. GaneshAssistant ProfessorDept. of Mechanical Engg.GECBH

Project Members:Akhil S (10)Akhil.R (12)Nidheeesh T T (4)

To develop more efficient and cost-effective small-scale H2 liquefiers as

an alternative to vapour-compression cycles using Magnetic

refrigeration (adiabatic magnetization)

To understand the Principle and mechanism for generating cooling

effect using the magnet.

Magnetic refrigeration is a cooling technology based on the magneto caloric effect.

This technique can be used to attain extremely low temperatures (well below 1

Kelvin), as well as the ranges used in common refrigerators, depending on the design

of the system.

It is a physical process that exploits the magnetic properties of certain solid materials

to produce refrigeration.

The refrigerant is often a paramagnetic salt, such as cerium magnesium nitrate.

It gives cooling nearest to absolute zero than any other method hence it made

liquidification of gases easier.

At the same time it does not emit any CFC or HCFC compounds hence it never

affects our environment specially OZONE layer.

Magneto caloric effect was discovered in pure iron in 1881 by E. Warburg.

DeDebye (1926) & Giauque (1927) proposed a improved technique of cooling

via adiabatic demagnetization independently.

The cooling technology was first demonstrated experimentally in 1933 by

chemist Nobel Laureate William F.Giauque & his colleague Dr.D.P. MacDougall

for cryogenic purposes.

In 1997,Prof. Karl A. Gscheidner, Jr. by the lowa State University at Ames

Laboratory demonstrated the first near room temperature proof of concept

magnetic refrigerator.

MCE is a magneto-thermodynamic phenomenon in which a reversible change

in temperature of a suitable material is caused by exposing the material to

changing magnetic field.

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-versa. At curie

temperature as magnet looses energy to the media it regains the property.

• Process is similar to gascompression and expansioncycle as used in regularrefrigeration cycle

• Steps of thermodynamic Cycle :->

Adiabatic Magnetization

Isomagnetic Enthalpy Transfer

Adiabatic demagnetization

Isomagnetic Entropic Transfer

Substance placed in insulated environment

Magnetic field +H increased

This causes the magnetic dipoles of the atoms to align

The net result is that total Entropy of the item is not reduced and item heats up (T + ΔTad )

Added heat removed by a fluid like water or helium (-Q)

Magnetic Field held constant to prevent the dipoles from reabsorbing the

heat.

After a sufficient cooling Magnetocalric material and coolant are

separated(H=0)

Substance returned to another adiabatic(insulated) condition

Entropy remains constant

Magnetic field is decreased

Thermal Energy causes the Magnetic moments to overcome thefield and sample cools(adiabatic temperature change)

Energy transfers from thermal entropy to magnetic entropy(disorderof the magnetic dipoles)

Material is placed in thermal contact with the Environment being

refrigerated.

Magnetic field held constant to prevent material 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

equilibrium, the cycle continuous.

Components required for construction :-

Magnets

Hot Heat exchanger

Cold Heat Exchanger

Drive

Magneto caloric wheel

Magnetic Materials

Regenerators

Super Conducting Magnets

Active Magnetic Regenerators

MCE is an intrinsic property of a magnetic solid

Ease of application and removal of magnetic effect is most desired

property of material

Alloys of gadolinium produce 3 to 4 K per tesla of change in magnetic field

are used for magnetic refrigeration or power generation purposes

ferrimagnets, antiferromagnets and spin glass systems are not suitable for

this application.

Gd5(SixGe1 − x)4, La(FexSi1 − x)13Hx and MnFeP1 − xAsx alloys are some of the

most promising substitutes for Gadolinium and its alloys

Magnetic refrigeration requires excellent heat transfer to and from thesolid magnetic material. Efficient heat transfer requires the large surfaceareas offered by porous materials. When these porous solids are used inrefrigerators, they are referred to as “Regenerators”

Typical regenerator geometries include:

• Tubes

• Perforated plates

• Wire screens

• Particle beds

Most practical magnetic refrigerators are based on superconducting magnets operating at cryogenic temperatures (i.e., at -269 C or 4 K)

These devices are electromagnets that conduct electricity with essentially no resistive losses.

The superconducting wire most commonly used is made of a Niobium-Titanium alloy

A regenerator that undergoes cyclic heat transfer operations and themagneto caloric effect is called an Active Magnetic Regenerator.

An AMR should be designed to possess the following attributes:-

High heat transfer rate

High magneto caloric effect

Sufficient structural integrity

Low thermal conduction in the direction of fluid flow

Affordable materials

Ease of manufacture

TECHNICAL

• High Efficiency

• Reduced Operating Cost

• Compactness

• Reliability

SOCIO-ECONOMIC

• Competition in Global Market

• Low Capital Cost

• Key Factor to new technologies

At the present stage of the development of magnetic refrigerators with

permanent magnets, hardly any freezing applications are feasible.

Some of the future applications are:-

Magnetic household refrigeration appliances

Magnetic cooling and air conditioning in buildings and houses

Central cooling system

Refrigeration in medicine

Cooling in food industry and storage

Cooling in transportation

Cooling of electronic equipments

Purchase cost may be high, but running costs are 20% less than theconventional chillers.

Thus life cycle cost is much less.

Ozone depleting refrigerants are avoided in this system, hence it moreeco-friendly.

Energy conservation and reducing the energy costs are addedadvantages.

The efficiency of magnetic refrigeration is 60% to 70% as compared toCarnot cycle.

Magnetic refrigeration is totally maintenance free & mechanically simplein construction.

As every coin has 2 sides, this technique also posses some drawbacks to be worked on

The initial investment is more as compared with conventionalrefrigeration.

The magneto caloric materials are rare earth materials hence theiravailability also adds up an disadvantage in MAGNETIC REFRIGERATION.

It is a technology that has proven to be environmentally safe. Computermodels have shown 25% efficiency improvement over vapor compressionSystems.

In order to make the magnetic refrigerator commercially Viable, scientistsneed to know how to achieve larger temperature swings and alsopermanent magnets which can produce strong magnetic fields of order10 tesla.

There are still some thermal and magnetic hysteresis problems to beSolved for the materials that exhibit the MCE to become really useful.