JOURNAL OF INTERNATIONAL ACADEMIC RESEARCH FOR MULTIDISCIPLINARY Impact Factor 2.417, ISSN: , Volume 3, Issue 10, November 2015

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1 OZONE LAYER DEPLETION AND ITS PREVENTION BY USING ECO- FRIENDLY ALTERNATIVE MAGNETIC REFRIGERATION TECHNIQUE MANI PAUL* DR.RAHUL DAS** *Centre for Himalayan Studies, University of North Bengal, Darjeeling, India **Dept. of Physics, A. B.N. Seal College, Cooch Behar, India ABSTRACT Ozone (O3) layer plays an important role for human s survival. The major role of the stratospheric ozone layer is to prevent the Ultraviolet (UV) Beta radiations ( nm) to reach the biosphere. This solar radiation has potential impacts on the biosphere, human health and natural eco-systems etc. The Chlorofluorocarbons (CFCs), Hydrochlorofluorocarbon (HCFCs) and other organo-halogens lead to the depletion of ozone layer. The non-natural easily liquefied CFCs, HCFCs were artificially developed by human to use as refrigerants. The development of a new solid state refrigeration technology, based upon the magnetocaloric effect (MCE), has brought an alternative to the CFCs or HCFCs gas compression refrigeration technique. In the MCE based solid state refrigeration systems, the maximum value of refrigerant capacity (RC) can be achieved up to 10 µb/atom. The objective of this paper is to study the origin and control of that by using eco-friendly alternative magnetic refrigeration technique. KEYWORDS: Ozone Layer Depletion; Refrigeration Technique; Magnetocaloric Effect; Refrigerant Capacity.. I.INTRODUCTION Ozone forms a protective layer which located in the stratosphere. Absorbing harmful UV Beta radiations ( nm) this layer protects the human life and the whole ecosystem [1] [4]. But the O3 layer has been damaged by CFCs, HCFCs and other chemicals emitted into the atmosphere due to several human s activities [5]. Modern human life style relies very much on readily available refrigeration technique at the domestic, commercial and industrial levels. The compressing and expanding processes of CFCs or HCFCs gas have been mainly used for cooling applications. These gases are able to travel through the troposphere to the stratosphere. The chlorine atoms of CFCs or HCFCs react very rapidly with ozone producing their oxide and thus deplete ozone in the stratosphere. Recently, the MCE based solid state refrigeration technique has brought an alternative to the conventional 104

2 gas compression technique [6] [7]. This MCE based refrigeration technique shows several advantages over the gas compression technique [7] in terms of cooling efficiency, compactly, power consumption and eco-friendly etc. Magnetic cycle can approach the efficiency of the Carnot cycle. Thus, due to low cooling efficiency of gas compression technique and concern for the environment, main efforts are now being directed to develop more eco friendly, cost effective, efficient, simple in design, convenient and reliable alternative MCE based solid state refrigeration systems. The objective of this article is to study the origin of ozone layer depletion and its prevention by changing the concept of refrigeration technique. II. OZONE LAYER AND ITS DEPLETION The O 3 layer spreads in the stratosphere (12-50 km above the earth s surface) which contains 90 % of all O 3 in the atmosphere [8]. In 1913, this layer first discovered by Charles Fabry and Henri Buisson. Then its properties have been explored by G. M. B. Dobson [9]. As a result of the dissociation of oxygen molecule (O 2 ) by the intense UV ray of solar radiation, the stratospheric O 3 is produced. In this case each stratospheric O 2 molecule is broken into two oxygen atoms (O + O) by absorbing UV ray of the solar radiation. Then an oxygen atom (O) combines with an O 2 molecule to form an O 3 molecule which is shown in Figure 1. And Equation 1 represents the overall reaction of O 3 formation [10]. O UV Radiation OO 2 OO O 2 3 O OO 2 3 Reaction of O 3 formation: (1) 3O2UV Radiation 2O3 Stratospheric O 3 is also naturally broken down to O and O 2 by photolysis which is shown by Equation 2 [10]. There is a balance between the rates of formation and destruction of the O 3. Thus, the total concentration of the stratospheric O 3 almost constant. O UV Radiation O O 3 2 OO O O Photolysis reaction of O 3: (2) 2O3UV Radiation 3O2 105

3 Absorbing most of the harmful solar energies including the UV beta radiations, this stratospheric layer plays a very important role for the protection of the life on this planet as well as maintains the present climate conditions familiar to the ecosystem. From many scientific results it is clear that the balance between the rates of formation and destruction of the O 3 is disturbed by the CFCs, HCFCs and other chemicals which are produced by human itself. As a result of this disturbance, the rate of conversion of O 3 to O 2 increases. In 1974, F. S. Rowland, M. J. Molina and Irvine reported the possible effects of CFCs on the layer of O 3, human life and the eco-system. Because of thermal and chemical stabilities, CFCs able to reach the stratosphere. These CFCs are decomposed by UV Beta radiation of the sun, releasing free chlorine (Cl) atoms which react with O 3 shown in Figure 2. The short lived product, ClO again reacts with a free O atom leaving the free Cl atom which ready to decompose another O 3 molecule. Thus stratospheric O 3 balance has been shifted and O 3 depletion occurs. III. MAGNETO-CALORIC BASED MAGNETIC REFRIGERATION SYSTEM Nowadays, all of us rely too much on cooling technology for food safety, comfort, medical and industrial applications. As an example, 15 % of the total worldwide energy is consumed for refrigeration purposes [11]. Until now, the most commonly used cooling devices are based on the gas-compression and expansion technology which use O 3 depletion agents such as CFCs and HCFCs that are detrimental to our living environment. Recent development of new solid-sate cooling technology based upon MCE [12] [13] has brought a green alternative to the conventional gas compression one [6], [14]. MCE based refrigeration has several advantages over the gas compression technology [6], [15] as listed below: 1. Magnetic refrigerator does not use O 3 depletion agents and is therefore an environment friendly cooling technology. 2. Magnetic refrigerator can reach higher cooling efficiency of up to 30 60% of a Carnot cycle, while the gas compression refrigeration has not crossed the 10% limit. 3. Magnetic refrigerators can be more compactly built even at a small scale, enabling the development of portable, battery-powered products. An example of refrigeration cycle for a MCE based refrigerator is shown in Figure 3 [16]. Initially, the material is in its ground state with randomly oriented spins. Due to the application of magnetic field, the spins are aligned resulting in heating of the material. This heat is removed from the magneto-caloric material to its surrounding by a heat-transfer 106

4 medium. On removing the field, the spins are randomized. In doing so, the temperature of the material has been reduced to below the ambient temperature. At this condition, the material can accept heat from an external load. This would cool the external load and in processes would raise the temperature of the MCE material to ambient value. This is the working principle of a magnetic refrigerator cycle which is very similar to the adiabatic-isothermal vapor compression cycle used in conventional refrigeration technology. IV. OPTIMISTIC ESTIMATE OF MAGNETIC REFRIGERANT CAPACITY The efficiency of a magneto-caloric material as a magnetic refrigerant is defined in terms of its refrigerant capacity (RC). It is a measure of the amount of heat that can be transferred between hot and cold reservoirs in an ideal refrigeration cycle. If there are two different magnetic refrigerants which differ only in their RC value, then the one with higher RC is expected to perform better because of its capability to transport larger amounts of heat in a real cycle [17]. RC can be estimated by integrating the isothermal magnetic entropy change S M with respect to temperature over the full width at half maximum (FWHM) of S M (T) curve [17] [19]. Mathematically, the procedure to obtaining RC is expressed as T 2 1 RC S T, H dt (3) T M Again the S M can be expressed by well-known thermodynamic Maxwell relation as M H SM 0 T H dh (4) It is cleared from equations (3) and (4) that for 1 T field change, the RC equals the change of magnetization M. But from the general principles, it is known that magnetization can vary between 0 to 10 µ B /atom [20]. Thus, optimum value of RC can be achieved up to 10 µ B /atom. It is believed that the magnetic materials with the higher RC around room temperature in addition to cheap materials cost will be the option of future solid state refrigeration technology. V. CONCLUSIONS The MCE based alternative refrigeration technique described in this study are still in the stage of infancy. But researchers are confident that without using O 3 layer depletion agents, the simple MCE based refrigeration technique will be convenient and reliable technologies for future domestic and commercial cooling system. In this article a simple method to 107

5 estimate RC of magnetic refrigeration is presented and shown that the optimum value of RC can be achieved up to 10 µ B /atom. REFERENCES 1. A. Aggarwal, R. Kumari, N. Mehla, Deepali, R. P. Singh, S. Bhatnagar, K. Sharma, K. Sharma, A. Vashishtha, and B. Rathi, Am. J. Plant Sci., vol. 4, p. 1990, A. M. Middlebrook, and M. A. Tolbert, Stratospheric Ozone Depletion. California: University Science Books, A. M. Tishin and Y. I. Spichkin, The Magnetocaloric Effect and Its Applications. Bristol: Institute of Physics Publishing, D. Lubin, J. E. Fredrick, C. R. Both, T. Locas, and D. Nueschuler., Geophys. Res. Lett., vol. 16, p. 783, E. Bruck, J. Phys. D: Appl. Phys., vol. 38, p. R381, E. Bruck, J. Phys. D: Appl. Phys., vol. 38, p. R381, E. Warburg, Ann. Phys., vol. 13, p. 141, J. E. Fredrick, and D. Lubn, Photochemmistry. In The Science of Photobiology. New York: Plenum Press, K. A. Gschneidner, Jr., and V. K. Pecharsky, Int. J. Refrig., vol. 31, p. 945, M. H. Phan, and S. C. Yu, J. Magn. Magn. Mater., vol. 308, p. 325, N. S. Bingham, M. H. Phan, H. Srikanth, M. A. Torija and C. Leighton, J. Appl Phys., vol. 106, p , T. Sivasakthivel, and K. K. Siva Kumar Reddy, Int. J. of Environ. Sci. Dev., vol.2, p. 30, United Nations Environment Programme, Environmental Effects Assessment Panel, Environmental Effects of Ozone Depletion and Its Interactions with Climate Change. Progress Report, V. Franco, J. S. Bl azquez, B. Ingale, and A. Conde, Annu. Rev. Mater. Res., vol. 42, p. 305, V. I. Zverev, A. M. Tishin, and M. D. Kuz min, J. Appl. Phys., vol. 107, p , V. K. Pecharsky and K. A. Gschneidner, Jr., J. Appl. Phys. Vol. 90, p. 4614, V. K. Pecharsky, K. A. Gschneidner, and A. O. Tsokol, Rep. Prog. Phys., vol. 68, p. 1479, V. K. Sharma, M. K. Chattopadhyay, R. Kumar, T. Ganguli, P. Tiwari and S. B. Roy, J. Phys.: Condens. Matter, vol. 19, p , World Meteorological Organization (WMO), Scientific Assessment of Ozone Depletion: Report No. 44. World Meteorological Organization, Geneva: Y. Matsumi and M. Kawasaki, Chem. Rev., vol. 103, p. 4767, Figures: Figure 1: Schematic diagram for formation of the O 3 molecules. 108

6 Figure 2: Schematic representation for the destruction of O 3 by the CFC molecule. Figure 3: Schematic diagram of a magneto-caloric material undergoing a magnetic refrigeration cycle. 109