APPLICATION OF MAGENTOCALORIC EFFECT IN REFRIGERATOR: A REVIEW ON RECENT RESEARCH

Author: Giridharan. V B.E. Mechanical

The peak C.O.P of vapor compression system is nearly reached and the world is trying to innovate new method and techniques. Many scientists planned to pursue refrigeration with other method than currently using vapor compression refrigeration.

There comes the use of Magnetocaloric effect in refrigeration. After this technology implemented, the field of Cryogenics laid its foundation strongly.

Now this technology is trying to change world of refrigeration from the Vapor compression system accompanied with 25% * increased efficiency and energy-saver.This system does not uses very harmful refrigerants (Eco – friendly).

INTRODUCTION

Magentocaloric effect was discovered in 1881, by warburg in iron material.

The first working magentic refrigerator was constructed in 1933.

From 1967, for generation of cryogenic temperature this effect is used.

Giant Magnetocaloric refrigerator (GMCE) in 1997 by Pecharsky and Gschneidner.

HISTORY:

This effect is derived from the Magnetic Refrigeration.

By Magnetizing and demagnetizing a semiconductor intrinsic material using external magnetic field generates heat and cold alternatively.

The magnetic field generates low entropy along with heat generation due to dipoles alignment. And while demagnetizing the entropy increases with decrease in temperature.

MAGNETOCALORIC EFFECT

BOLTZMANN DISTRIBUTION LAW OF MAGNETIC FIELDS

This law often explains the reason for the generation of heat while magnetizing a paramagnetic material.

The property changes over to ferromagnetic accompanied with heat.

Magnetocaloric refrigerator will takes off the usage of current vapor compression refrigerators and also the usage of harmful refrigerants.

The processes are similar to vapor compression refrigerator, but instead of increasing pressure here magnetic field. The steps are given below,

1. Adiabatic Magnetiation

2. Heat Rejection

3. Adiabatic Demagnetization

4. Evaporator.

MCE IN HOME REFRIGERATOR APPLIANCE

Here the material is subjected to external magnetic field (adiabatically), thereby alignment of electrons according to their respective energy levels takes place.

Thus the magnetic entropy of semiconductor intrinsic material reduces while the lattice vibrations (Phonons) increases due to temperature increase.

The total entropy of the system is given by the equation, S (T; H) = S m(T; H) + S lat(T)

The forced alignment of electrons from its original position liberates energy in the form of heat.

ADIABATIC MAGNETIZATION

ADIABATIC VS ISOTHERMAL MAGNETISATION

In this process the heat generated in the material is taken out by cooling up to surrounding temperature.

This procedure involves the use of heat exchangers to transfer heat to the surroundings.

In reality the material is covered by condensing liquid, over that external magnetic field is placed.

HEAT REJECTION

Demagnetization of magnetic material causes the alignment of electrons to its original state. This process is done adiabatically, as the system already reaches the surrounding temperature.

While demagnetizing the electron accommodate their original places by absorbing heat.

when the system is insulated the material temperature reduces than the surrounding temperature.

Thereby cooling takes place.

ADIABATIC DEMAGNETIZATION

In case of entropy change, while demagnetizing the magnetic entropy comes near to its original state.

The alignment of electrons causes absorption of heat, hence the lattice vibrations reduces.

Thus the value of lattice entropy due to temperature decreases.

But the total entropy of the system remains constant.

Demagnetizing means reducing the magnetic field to fewer, instead of zeroing it.

Evaporator process is same as in vapor compression refrigeration which makes the area to cool.

Once the material temperature becomes less than surroundings, the refrigerant is allowed to takes away the cold and made to be in contact with atmosphere to be refrigerated.

Since the temperature of refrigerant is less than the atmosphere, heat flows towards refrigerator. This goes on until both the refrigerant and refrigeration atmospheric temperature become same.

EVAPORATOR

The refrigerant used in magnetic refrigeration is Helium (He).

The property of helium is liquid when it is less than 4.2 K.

At room temperature it is in gaseous form.

The use of helium as a refrigerant is because of its property, it remains liquid even at extremely low temperature other refrigerants may become solid at that temperature.

REFRIGERANT

For the past 20 years research were undergone to invent a material to show magnetocaloric effect at room temperatures.

The materials used in industries for huge refrigeration failed to produce MCE at room temperature.

It has been found that Lanthanide group elements can generate high Magnetocaloric effect than iron. Example: Gadolinium.

When these materials are alloyed with other elements their properties changes .

Example: MnFe(P1-xGex)

MAGNETIC MATERIAL

Some near room temperature magnetic materials

MAGNETIC REFRGERATOR TYPES

Linear Magnetic Refrigerator

Radial Magnetic Refrigerator

(A)Refers Magnetization part(B)Refers Demagnetization part

Prototype Build by General Electrics, US. (2014)

Problems facing....

1. Cost of the materials used are higher than vapor compression refrigerator.

2. Compared with the size of compressor the size of this system is large and trying to accommodate in small vessel.

3. Selection of magnetic material – since the Lanthanide elements are unstable, they are toxic in natural. Alloying of such elements may eliminate toxicity.

4. The usage of this refrigerator is made similar to currently using vapor compression refrigerators

ADVANTAGES

1. 20 – 25% increased power consumption

2. Faster rate of cooling than vapor compression refrigeration.

3. Very Low temperature can also be achieved (record ~ 0.3K).

DISADVANTAGES

4. Permanent magnets have limited field, electromagnets increases the cost.

5. The Magnetic material using is toxic due to unstable.

6. Complex in nature than vapor compression refrigeration.

60% carnot efficiency by Magnetic refrigeration

CONCLUSION

This system of refrigeration will change the entire world from current compressor refrigeration. By saving ~25% of electricity at refrigerators in all homes and industries cause tremendous change in energy saving and power production.

And the use of non – toxic refrigerant helps to reduce the green house gas emission in atmosphere makes it eco-friendly. This type of refrigeration will change the world of refrigeration.

FUTURE TRENDS

o This technology will be available in market in 2020 price similar to compression refrigeration.

o This system will also likely to be implemented in air – conditioning and its outline was done by RUSSEK and ZIMM in IIR.

o Research are undergoing to reduce the operation cost of producing gas at lower temperature.

REFERENCES

[1] Prakash Chawla and Ankit Mathur. A Review Paper on Development of

Magnetic Refrigerator at Room Temperature. IJIRSE Vol. 3/ Iss. 3/ page no.126 – 140.[2] Danmin Liu, Ming Yue, et al. Origin and tuning of the magnetocaloric

effect for the magnetic refrigerant MnFe(P1-xGex).

[3] http://www.tesisenred.net/bitstream/handle/10803/1789/1.CHAPTER_1.pdf?sequence=2. The Magnetocaloric Effect, dated on 09-04-2016.[4] Pecharsky V K, Gschneidner Jr K A. Advanced magnetocaloric materials:

What does the future hold [J]. International Journal of Refrigeration, 2006, 29(8):1239−1249.[5] Russek S L, Zimm C. Potential for cost effective magnetocaloric air

conditioning systems [C]// Proceedings of the First IIF–IIR. International Conference on Magnetic Refrigeration at Room Temperature. Montreux, Switzerland, 2005.

[6] Pecharsky, V. K.; Gschneidner, Jr., K. A.(1997). “Giant Magnetocaloric

Effect in Gd_{5}(Si_{2}Ge_{2})". Physical Review Letters 78 (23): 4494. doi:10.1103/PhysRevLett.78.4494.[7] Dr. Kai Hock (2012-2013). Magnetic cooling. Statistical and low temperature physics (PHYS393), University of Liverpool.[8] http://mriquestions.com/fall-to-lowest-state.html, Boltzmann distribution

of energy states, dated on 10-04-2016.[9] Magnetocaloric Refrigerator Freezer- A Peer Review, CREDA and GE, 2014.[10] “GE magnetic refrigeration breakthrough”, You tube, dated 06-04-2016.

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