The term Refrigeration could be understood as a method of removing heat from a substance which could be in any state of matter solid, liquid, or gas. In the process of removing heat from the substance the substance gets cooled. In refrigeration, a refrigerant is a substance which is capable of transferring heat from low temperatures and pressures to a condensing substance at higher temperatures and pressures. By means of expansion, compression, and a cooling substance, such as air or water, the refrigerant removes heat from a substance and transfers it to the cooling substance.
The magnetic refrigerator, which has advantages in the field of refrigeration performance coefficient, reliability, low noisiness and environmental friendliness with respect to the conventional gas type refrigerators, is becoming an upcoming technology to alternate the conventional technique.
The study of magnetic refrigeration which was started with the discovery of magneto-caloric effect (MCE) was first discovered by Warburg in 1881. In 90s Tesla and Edison independently tried to get benefited from this effect by running heat engines which couldn’t be made successful. Later on Weiss and Piccard explained the magneto-caloric effect in detail. Later Debye and Giauque developed a new method of magnetic refrigeration for sub-zero temperatures in order to achieve sub-Kelvin temperatures. Later on Giauque and MacDougall successfully verified their method and compute their idea by an experimental test rig. After that this technology has been used in cryogenic refrigeration purposes.
Magnetic refrigeration is based on a basic thermodynamic property of magnetic materials this is known as Magneto-caloric effect, which causes a temperature decrement of the material if it is subject to an applied magnetic field under adiabatic conditions.
A German scientist Warburg first proposed the thermal effect of iron when it is subjected to a varying magnetic field. Debye and Giauque then explained the nature of this effect afterwards and proposed the achieving of an ultra-low temperature by using adiabatic demagnetization cooling. In past recent years many magnetic refrigerators based of MCE has been developed for room temperature range.
Magnetic refrigeration depends upon the regenerative temperature change, its been discovered that some materials exhibit magnetocaloric effect when exposed to a changing magnetic field. In these materials, a massive change in entropy is noticed by applying & removing of the magnetic field, and the adiabatic magnetic field changes are comparable with adiabatic pressure change on gases. Thus by varying the magnetic field on a material, work is performed and the internal energy of the system changes. Thus this differential variation in the internal energy of material can be achieved by a magnetic work transfer given by the results of the applied magnetic field, and the variation in magnetizing power.
When a magneto-caloric material like those mentioned above is subjected to a strong magnetic field (Tesla), the electrons revolving within the material are forced to align symmetrically with the magnetic field. This means, our magnetic field does the work to align all the electrons which spins into arrangement which is, thermodynamically, a low energy state to achieve stability. The energy exerted during this alignment causes the temperature of the material to increase. When this magnetic field is lowered, the electrons return to a greater random state which is a higher energy state absorbing heat from the surrounding and causing the temperature to fall.
Many researchers have been done on the magnetocaloric effect over the past many years. A number of room temperature magnetic refrigerators are proposed every decade since 1970. If we see the future perspectives of room temperature magnetic Refrigeration system, it can be seen from the earlier discussion on magnetic refrigeration that main progress have been made in America. However, with the continual progress of room temperature magnetic refrigeration, the whole world has accelerated their research in this field. With the former results achieved by researchers, it could be notified that there is still a large performance difference between magnetic refrigerator and vapour compression refrigerator in terms of cooling capacity and temperature span.
Various efforts of gaining low temperature spaces are made by the students of Mechanical engineering of Sagar Group of Institutions SISTec in their final year. Magnetic refrigeration is a technology of leading-edge generation and we here in SISTec are putting our efforts to apply this new tech in an indigenous way to take a step further to contribute in “Make in India”.
Prof. Ashank Vishwakarma
Dept of Mechanical Engineering
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