VIII SEM ME
Department of Mechanical Engineering
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.
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 a versa
at curie temperature as magnet looses energy to the media it regains the
• Process is similar to gas
compression and expansion
cycle as used in regular
• Steps of thermodynamic Cycle :->
Isomagnetic Enthalpy Transfer
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
Substance returned to another adiabatic(insulated) condition
Entropy remains constant
Magnetic field is decreased
Thermal Energy causes the Magnetic moments to overcome the
field and sample cools(adiabatic temperature change)
Energy transfers from thermal entropy to magnetic entropy(disorder
of the magnetic dipoles)
Material is placed in thermal contact with the Environment being
Magnetic field held constant to prevent material from heating back
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
Hot Heat exchanger
Cold Heat Exchanger
Magneto caloric wheel
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
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 the
solid magnetic material. Efficient heat transfer requires the large surface
areas offered by porous materials. When these porous solids are used in
refrigerators, they are referred to as “Regenerators”
• 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
A regenerator that undergoes cyclic heat transfer operations and the
magneto 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
Ease of manufacture
• High Efficiency
• Reduced Operating Cost
• Competition in Global Market
• Low Capital Cost
• Key Factor to new
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 the
Thus life cycle cost is much less.
Ozone depleting refrigerants are avoided in this system, hence it more
Energy conservation and reducing the energy costs are added advantages.
The efficiency of magnetic refrigeration is 60% to 70% as compared to
Magnetic refrigeration is totally maintenance free & mechanically simple
As every coin has 2 sides, this technique also posses some
drawbacks to be worked on
The initial investment is more as compared with conventional
The magneto caloric materials are rare earth materials hence their
availability also adds up an disadvantage in MAGNETIC REFRIGERATION.
It is a technology that has proven to be environmentally safe. Computer
models have shown 25% efficiency improvement over vapor compression
In order to make the magnetic refrigerator commercially Viable, scientists
need to know how to achieve larger temperature swings and also
permanent magnets which can produce strong magnetic fields of order
There are still some thermal and magnetic hysteresis problems to be
Solved for the materials that exhibit the MCE to become really useful.