APPLICATION OF MAGNETOCALORIC EFFECT IN REFRIGERATOR: A REVIEW

ON RECENT RESEARCH

V. Giridharan1, R. Gokulakrishnan2 and P. Kumaran3

Department of Mechanical Engineering, Aarupadai Veedu Institute of Technology,

Paiyanoor, Chennai- 603 104, Tamilnadu, India.

Email: giridharanv97@yahoo.in ; adolfgokul863@gmail.com ; kumaran5666@gmail.com.

Tel: +91-9176850215; +91-9962737455; +91-9445242621.

Abstract

Demagnetizing of some semi-conducting materials causes enormous cooling to the system.

The technical application of these basic studies would be revolutionizing the refrigeration industry.

This eco-friendly technology is likely to replace the usage of existing compressors in vapor

compression system at future. The basic theory of Magnetocaloric effect and implementation of

study into technology are reviewed in detail. This article will also elucidate the use of this high end

technology for home refrigerators and the material selection for this operation.

Keywords: Magnetic cooling, Semiconducting material, Demagnetizing, Magnetocaloric Effect.

1. INTRODUCTION

The effect of cooling paramagnetic material by using magnetic field was proposed by French

Physicist P. Weiss and Swiss Physicist A. Piccard in 1917 and its fundamental principle and

derivations was done by P. Debye (1926) and W. Giauque (1927). The recent research on

refrigeration was mainly on eliminating the compressor of vapor compression system as its

efficiency nearly reached peak (C.O.P up to 2.2) and also to eliminate use of toxic refrigerants. This

technology produces 25% more efficiency than commercially using vapor compression systems.

Magnetizing and demagnetizing of paramagnetic element causes change in entropy leads to heating

and cooling. This effect is called as Magnetocaloric effect.

2. BASIC THEORY

The principle of this technology is based on static thermodynamics and physics. The alignment

of +1/2 and -1/2 spin electron follows Boltzmann Distribution of energy states[8] (i.e. no. of higher

energy electrons to be less) thereby the higher energy electron lowers down with the ejection of

heat. This heat is convected from system. While demagnetizing the entropy becomes reduces leads

to the cooling of material less than the surroundings. The property of magnet changes from

paramagnetic to ferromagnetic and returns to paramagnetic. The gap between the energy levels

depends upon the magnetic field intensity. By magnetizing both magnetic entropy (S m) and lattice

entropy (lattice vibration – S lat) occurs and is given by the equation [3],

S (T; H) = S m(T; H) + S lat(T)

3. MAGNETOCALORIC APPLICATION IN REFRIGERATORS:

The use of magnetocaloric effect in home refrigerators is typically different from very low

temperature refrigeration. In home appliance we cool the substance up to – 240C. Refrigeration

steps involved are similar to vapor compression system. But instead of increasing pressure, we

increase the magnetic field.

Figure 1: Prototype of Axial Type Magnetocaloric Refrigerator for home appliance by GE [9].

3.1. ADIABATIC MAGNETIZATION

Magnetizing the material adiabatically causes the

alignment of spin electrons in higher energy and lower

energy respectively. Consequently, the paramagnetic

become ferromagnetic with the release of heat and

decreased magnetic entropy (S m). Whereas the total

entropy remains constant due to lattice vibrations(S lat) by

temperature change. The increase in temperature should be less than the curie temperature of Ferro

magnet. The external magnetic field is made constant to

maintain temperature and entropy. From figure 1 the presence of two axial magnet refrigerators.

When it rotates clockwise it increases the magnetic field and demagnetization occurs in

counterclockwise. The temperature change due to adiabatic magnetization is given by the equation

[1],

Where, μ0 is the permeability of vacuum,

H0 and H1 are the initial and final magnetic field.

3.2. HEAT REJECTION

The heat formed by the material is taken away by using pumps. The cooling fluid is layered over

the material takes the heat and also to maintain the total entropy of the system. The heat exchangers

are used to transfer heat to atmosphere and the liquid is again reused for cooling.

3.3. ADIABATIC DEMAGNETIZATION

The material is adiabatically demagnetized up to fewer magnetic fields. Consequently, the

entropy and lattice entropy reduces maintains the total entropy constant. The electrons return to

Figure 2: Steps of Magnetocaloric Refrigeration [1].

their respective directions by absorbing heat energy, which lowers the material temperature. By

repeating magnetizing and demagnetizing we can achieve gradual cooling till very low temperature

which is impossible by vapor compression system. The lattice entropy is proportional to the

temperature change as it decreases the temperature also reduces.

3.4. EVAPORATOR

This processes uses refrigerant (He- Helium) to absorb the heat from the atmosphere to be

refrigerated. The refrigerant is pumped to made contact with the material with low temperature and

it condenses which is again made constant with the refrigerator atmosphere. This process is similar

to the evaporator in vapor compression system. This cycle goes again and again.

4. MAGNETIC MATERIAL SELECTION FOR HOME REFRIGERATORS

As many Lanthanide elements possess Magnetocaloric effect, the most effective elements are Gd

(Gadolinium), Mn and so on. But they failed to exhibit the Magnetocaloric effect at room

temperature as the Curie temperature less than room temperature. Since these rare earth metals are

toxic they are alloyed with other metals to increase its curie temperature and also to reduce toxicity.

For operating at room temperature the preferable elements are,

GdSiGe [1] alloys, MnFe(P1-xGex) [2], MnAsSb [2] alloys. The magnetic field allowable must be less

than 5T (Tesla) for home refrigerators. Research is going on to reduce the cost of material with

alternates of same effectiveness.

Figure 3: Table of magnetic materials with different Curie temperature (TC), enthalpy and

entropy change [1].

Figure 4: S-T Curves of Gadolinium element Figure 5: C.O.P of Magnetocaloric

with different magnetic field [7] refrigeration with other systems [9]

5. ADVANTAGES

The following are the potential advantages of using magnetically cooled refrigeration,

25-35% of increased efficiency and also reduces power consumption.

Environmental friendly due to the use of non-toxic refrigerants.

It can achieve temperature nearly absolute zero and faster rate of cooling compression systems.

Less number of moving parts used for reduced noise.

6. DISADVANTAGES

Some compromising disadvantages are

The working material used is toxic in nature.

The cost of the material is very high and rare.

Complex in nature than Vapor compression refrigeration.

Permanent magnets have limited field strength, electromagnets are costlier too.

7. FUTURE SCOPE AND APPLICATIONS

This technology will be in market at 2020 with eco-friendly terms and reliable cost. Research is

going on to use this technology in air-conditioning to eliminate compressors there too. Reduces the

operation cost for producing gases at cryogenic temperatures. The potential for cost-effective

magnetocaloric air-conditioning systems was outlined by Russek and Zimm in the Bulletin of the

IIR [5]. This commendable technology will reduce the electricity consumption up to 20%* in future.

8. CONCLUSION

It is concluded that this room temperature MCE refrigerators generates efficiency of 60% Carnot

(from figure 4) [9] and the implementation of different magnetic material will reduce the cost. As the

whole world uses refrigerator, this technology reduces the electricity demand to high extend. And it

will avail in market with cost and size similar to vapor compression system in future.

9. 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.