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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.